7th Heidelberg International Symposium on High-Energy Gamma-Ray Astronomy

4 Jul 2022, 07:40 → 8 Jul 2022, 18:00 Europe/Madrid

Aula Magna (Facultat de Biologia, Universitat de Barcelona)

 

---

 

The 7th Heidelberg International Symposium on High-Energy Gamma-Ray Astronomy (γ-2022), will take place on July 4th to 8th 2022, in Barcelona, Spain.

The Gamma-Ray Symposium has been held since 1994 in Heidelberg, Germany (see the webpage of previous editions in 2000, 2004, 2008, 2012 and 2016). The 2020 edition had to be postponed due to the pandemic situation related to the COVID-19. We are now glad to announce that the Symposium will take place in 2022 and, for the first time, it will be held in Barcelona, hosted by the Institut de Ciències del Cosmos (ICCUB) of the University of Barcelona. It will closely follow the guidelines and structure of the previous Symposia, covering all major observational and theoretical aspects of the field with an emphasis on the high (GeV) and very high (TeV) energy intervals of the electromagnetic spectrum.

Scientific topics will range from the origin of galactic and extragalactic cosmic rays to the physics and astrophysics of compact objects and their relativistic outflows (Pulsars, Microquasars, Blazars, GRBs), PWNe, SNRs, Star Forming Regions, Giant molecular clouds and Interstellar Medium, as well as extragalactic non-thermal objects like Starburst Galaxies, Radio Galaxies and Galaxy Clusters. Cosmological issues related to Dark Matter, Intergalactic radiation and magnetic fields, and topics relevant to fundamental physics will also be addressed.

On behalf of LOC and SOC,
F. Aharonian, F. Rieger and J. M. Paredes

 

 

                                                                          Gamma-2022.pdf

 

---

 

Scientific Organising Committee   Felix Aharonian (DIAS / MPIK, chair) Elena Amato (INAF - Osservatorio Astrofisico di Arcetri) Xavier Barcons (ESO) Valenti Bosch-Ramon (UB / ICCUB) Zhen Cao (IHEP & Tianfu Cosmic Ray Research Center) Catherine Cesarsky (AIM, DAp, Université Paris Saclay) Paolo Coppi (Yale University) Emma De Ona Wilhelmi (ICE / DESY) Jim Hinton(MPIK) Werner Hofmann (MPIK) Michael Kramer (MPIfR) Martin Lemoine (IAP - CNRS / Sorbonne Université) Josep Martí­ (Universidad de Jaén) Manel Martí­nez (IFAE-BIST) Reshmi Mukherjee (Barnard College, Columbia University) Josep M. Paredes (UB / ICCUB, co-chair) Elena Pian (INAF-OAS) Elisa Resconi (Technische Universität München) Gustavo Romero (IAR-CONICET/CICPBA) Gavin Rowell (The University of Adelaide) Samar Safi-Harb (University of Manitoba) Eun-Suk Seo  (University of Maryland) Ronald Shellard (CBPF) Joe Silk (IAP/JHU) Christian Stegmann (DESY) Marco Tavani (INAF) Masahiro Teshima (ICRR, University of Tokyo / MPP) Jacco Vink (University of Amsterdam / API)  Xiang-Yu Wang (Nanjing University) Roberta Zanin  (CTA Observatory GmbH)

Local Organising Committee                 Arnau Aguasca-Cabot (UB/ICCUB) Anna Argudo (UB/ICCUB) Anna Bertolin (IEEC) Pol Bordas (UB / ICCUB) Valentí Bosch-Ramon (UB / ICCUB) Mar Carretero-Castrillo (UB/ICCUB) Daniel del Ser (UB / ICCUB / RACAB) Kazushi Iwasawa (UB / ICCUB) Eleni Kefala (UB/ICCUB)  Edgar Molina (UB / ICCUB) Pilar Montes (IEEC) Esther Pallarés (UB / ICCUB) Josep M. Paredes (UB / ICCUB, chair) Marc Ribó (UB / ICCUB) Frank Rieger (MPIK, co-chair) Gabriele Weese (MPIK) Xiying Zhang (UB / ICCUB)

 

---

                                       

                                          

Acknowledgements

This event is part of the grant CEX2019-000918-M funded by MCIN/AEI/10.13039/501100011033.

 

 

 

 

---

Gamma-2022 announcements anunci 2.pdf First announcement _2022.pdf

POSTER Poster Gamma 2022.pdf Poster Gamma 2022.png

venue venue_aula_magna.jpg venue_faculty.jpg

Monday 4 July

08:30 → 09:15 Registration

09:15 → 09:30 Welcome (Aula Magna Biologia)

Welcome.pdf

09:30 → 11:00 Review Talks: Monday (Aula Magna Biologia) Chair: Felix Aharonian

09:30 Theory of Gamma-Ray loud AGN

The last decade has seen tremendous developments in gamma-ray astronomy
with the extragalactic sky becoming highly populated by AGN.
I will highlight some of the progress in AGN research achieved over the
years, and then discuss exemplary advances in the theory of gamma-ray
loud AGN, including black-hole magnetospheric processes, the physics of
pc-scales jets, as well as particle acceleration and high-energy emission
in the large-scale jets of AGN.

Speaker: Frank Rieger (ITP Univ Heidelberg & MPIK)

ID498-FrankRieger_AGN_theory.pdf

10:15 A multi-wavelength View of Active Galactic Nuclei with an Emphasis on Gamma Rays

Active Galactic Nuclei (AGN) are quite unique astronomical sources emitting over about 20 orders of magnitude in frequency, with different electromagnetic bands providing windows on different sub-structures and their physics. They come in a large number of flavours only partially related to intrinsic differences. I will highlight the types of sources selected by different bands, the relevant selection effects and biases, and the underlying physical processes, emphasizing the gamma-ray band. I will then look at the “big picture” by describing the most important parameters one needs to describe the variety of AGN classes. I will then conclude with a look at the most pressing open issues and the main new facilities, which will flood us with new data to tackle them.

Speaker: Paolo Padovani (European Southern Observatory)

ID349-PaoloPadovani-multiwavelength_view_AGN.pdf

11:00 → 11:30 coffee break

11:30 → 12:20 Highlight Talks topical: Monday (Aula Magna Biologia) Chair: Gustavo E. Romero

11:30 GRBs and their afterglows at VHEs

Recently, the observational study of gamma-ray bursts (GRBs) in the very-high-energy (VHE) regime has advanced with several long-awaited detections with MAGIC and H.E.S.S. telescope systems. Currently, the list of GRBs with robustly measured VHE emissions contains GRB 180720B, GRB 190114C, and GRB 190829A. Three more bursts were reported as source candidates by the MAGIC Collaboration. This candidate list includes a short GRB, which was detected with low significance (GRB 160821B), and a very distant GRB 201216C (from z=1.1), which was detected with high significance (>5\sigma). Although in the latter case the analysis has still a preliminary status. Detection of GRB afterglows in the VHE regime allows obtaining essential information on particle acceleration by relativistic shock waves. This makes GRB afterglows to be important sources for high-energy astrophysics and their studies have an exceptionally broad scope. However, the extragalactic origin of GRB implies a severe constrain for their observational study in the VHE domain. Namely, attenuation of multi TeV photons by extragalactic background light (EBL) becomes significant at cosmological distances. The EBL absorption hardens the detection of GRBs and deforms their TeV spectrum, which makes nearly impossible any reliably determination of the intrinsic gamma-ray spectrum.  The fortunate proximity of one of the detected GRBs (GRB 190829A occurred at z~0.08) allowed an unexpectedly long signal detection, up to 56 hours after the trigger, and accurate spectral determination in a broad energy interval, spanning between 0.18 and 3.3TeV. The obtained temporal and spectral properties of the VHE emission appeared to be remarkably similar to those seen in the X-ray band with Swift-XRT. Comparison to other detected GRB afterglow shows that SEDs and lightcurves obtained from GRBs share much in common, which disfavors the chances for GRB 190829A being an exceptional event. This suggests a need for a revision of the theoretical scenarios used to
predict the broadband emission from GRB afterglows.

Speaker: Dmitry Khangulyan (Rikkyo University)

DmitryKhangulyan_GRBs_and_their_afterglows_at_VHEs.pdf

11:55 TeV Emission from GRB Afterglows - Theory

GRBs’ progenitors are also sources of gravitational waves. Binary neutron star mergers that are progenitors of short GRBs are the classical sources of chirping GW signals. Long GRBs arise from Collapsars. While GWs haven’t been observed yet from collapsing stars, a non-spherical collapse would be a source of a burst of GWs. In addition, both long and short GRBs involve the acceleration of relativistic jets. The acceleration of these jets is an additional source of memory type gravitational waves - Jet-GWs. The characteristic frequency depends on the acceleration mechanism and the duration of the jet, while the amplitude depends on the jet’s energy and its distance. Detection of Jet-GWs would reveal information on GRBs’ central engines and the jet acceleration mechanic that cannot be observed otherwise. While typical GRBs are too far for detection of their Jet-GWs in the near future, detection of Jet-GWs from hidden jets taking place within regular SNe is likely with next generation detectors. Detection of a jet within a galactic SGR giant-flare would be possible even with LIGO and Virgo.

Speaker: Prof. Tsvi Piran

12:20 → 13:10 Highlight Talks observational: Monday (Aula Magna Biologia) Chair: Gustavo E. Romero

12:20 Highlights from MAGIC

MAGIC is a system of two 17-m diameter Imaging Atmospheric Cherenkov Telescopes, located at an altitude of 2200 m in the Observatorio Roque de los Muchachos on the Canary island of La Palma. MAGIC provides a broad energy coverage, detecting gamma rays from 50 GeV and up to 100 TeV. The minimum energy can be further lowered to 15 GeV when using the SumTrigger specially optimised for low energies. A careful strategy of alert follow-ups from other facilities and the fast reposition of the telescopes as well as multi-wavelength campaigns are instrumental for the MAGIC observation program. In this presentation we will report the recent highlights from MAGIC. We will cover, among others: detections of gamma-ray burst at very high energies, the evidence for proton acceleration in the nova RS Ophiuchi, the extension of the spectra of Geminga pulsar at VHE, several campaigns on AGN and the dark matter searches.

Speaker: Oscar Blanch Bigas (IFAE)

20220704_Gamma22_MAGIC_highlihts_v1r0.pdf

12:45 Highlights from H.E.S.S.

The High Energy Stereoscopic System is the only facility available for studying the Very High Energy sky in the Southern Hemisphere. In 2019 it was upgraded with a new camera on its CT5 telescope and has been continuously operated during the Covid pandemic. During this period, new sources, source classes and phenomena were discovered and in-depth surveys and analyses were conducted. This presentation describes the highlights of H.E.S.S. observations during the last three years and presents an outlook for the newly approved extension of science operations.

Speaker: Stefan Wagner (LSW, ZAH, U Heidelberg)

gamma22_HESS_Wagner.pdf

13:10 → 15:00 lunch break

15:00 → 16:30 Contributed Talks: EGAL parallel 1 (Aula Magna Ciències de la Terra) Chair: Lea Heckmann

15:00 Shear acceleration in AGN jets

X-ray observations of kilo-parsec scale jets indicate that a synchrotron origin of the sustained non-thermal emission is likely. This requires distributed acceleration of electrons up to near PeV energies along the jet. The underlying acceleration mechanism is still unclear. Shear acceleration is a promising candidate. We studied the details of shear acceleration by solving the steady-state Fokker-Planck-type equation and provide a simple general solution for trans-relativistic jets for a range of magnetohydrodynamic turbulent power-law spectra. In general, the accelerated particle population is a power-law spectrum with an exponential-like cut-off, where the power-law index is determined by the turbulence spectrum and the balance of escape and acceleration of particles. We find that in this framework the multi-wavelength spectral energy distribution of X-ray jets, such as Centaurus A and 3C 273, can be well explained and protons can be accelerated up to $\sim$ EeV. Relativistic MHD simulations using PLUTO have been performed to physically motivate the shear profile and turbulence spectrum.

Speaker: Jieshuang Wang (Max-Planck-Institut für Kernphysik)

ID262-JieshuangWang-Shear_acceleration.pdf

15:15 Multiple shock acceleration in AGN jets

Radiogalaxies are the subclass of active galactic nuclei where large-scale relativistic jets are detected. In this work we study the acceleration of particles in a multiple shock scenario produced by the collision of the relativistic jets with embedded massive stars. We solve the transport equation taking into account not only the spatial and radiative losses but also the collective effect of the shocks and the possible reacceleration, and evaluate the maximum energies that the particles can achieve. Finally, we compute the gamma-ray emission expected in this scenario and discuss the detection possibilities.

Speaker: Ana Laura Müller (ELI Beamlines, Institute of Physics, Czech Academy of Sciences)

ID486-MuellerAnaLaura-Multiple_Shock_Acceleration.pdf

15:30 A multi-wavelength view of gamma-ray emitting extreme BL Lacertae blazar candidates hidden within Fermi-LAT data.

Blazars are key-elements in the understanding of the extragalactic gamma-ray sky. These sources are jetted radio-loud active galactic nuclei dominated by non-thermal emission that extends across the electromagnetic spectrum. Their emission is a proof of cosmic particle acceleration and the production of ultra-relativistic particles within the blazar structure, and are therefore excellent astroparticle physics laboratories. Particularly interesting are extreme high-synchrotron-peak (EHSP) blazars, a subtype of blazar whose gamma-ray emission is expected to peak at TeV energies, yet surprisingly they are a minority in very high energy source catalogs. In this talk, we show a model-driven methodology to search for EHSP blazars based on data from NASA's Fermi Gamma-ray Space Telescope in addition to archival radio, optical, and X-ray data. This method allows us to study their physical properties. Our main results are (1) finding 17 new EHSP blazars, increasing significantly their number, (2) that only 2 of them seem to be detectable by TeV telescopes, and (3) these 2 objects are outliers relative to their magnetic versus kinetic energy density. We discuss some interpretations of these results.

Speaker: Mireia Nievas Rosillo (IAC)

Extreme_EHSP_FermiHidden_Gamma2022_final.pdf

15:45 Absorption features in gamma-ray spectra of BL Lac objects

The production site of gamma rays in blazars is closely related to their interaction with the photon fields surrounding the active galactic nucleus. In this work we discuss an indirect method that may help to unveil the presence of ambient structures in BL Lacs through the analysis of their gamma-ray spectrum.
Passing through structures at different distances from the black hole, gamma rays interact with the corresponding photon fields via gamma-gamma pair production, producing absorption features in their spectral energy distribution. An interaction of the gamma-ray photons with a putative broad-line region may reduce the gamma-ray flux only if its production site were very close to the central engine. On the other hand, if jet photons interact with optical-UV seed photons produced by a pc-scale narrow-line region, the consequent gamma-gamma process may cause absorption features at a few hundreds GeV.
Sources with spectra reaching TeV energies, such as HBLs and EHBLs (extreme blazars), may represent exceptional probes to investigate this topic. In this regard, we discuss recent observations of sources which may show evidence of such absorption features in their gamma-ray spectra.
Finally, we discuss how sub-TeV absorption features in the spectra of BL Lacs may affect their broadband modeling, and eventually represent a powerful diagnostic tool to constrain the gamma-ray production site and the jet environment.

Speaker: Luca Foffano (INAF Rome (IAPS))

ID290_LucaFoffano_absorptionfeatures_at_gammarays_upload.pdf

16:00 1ES 0647+250: 10 years of multiwavelength observations

The High-peaked BL Lac object 1ES 0647+250 is one of the few distant blazars detected at very-high-energy (VHE, E > 100 GeV) gamma rays during non-flaring activity. Its redshift is still uncertain, but a lower limit of z>0.29 was recently calculated, based on the minimum equivalent width of absorption features expected from the host galaxy. This blazar was first detected by the MAGIC telescopes between 2009 and 2011 during its low state, displaying around 2% of the Crab Nebula flux above 100 GeV, but it has shown several periods of large activity, where the VHE gamma-ray flux increased by more than 1 order of magnitude. In this contribution, for the first time the detailed broadband spectral energy distribution (SED) will be presented for different activity levels. A long-term analysis of the variability displayed by this BL Lac object has been carried out using a rich MWL data sample extending more than 10 years. The long-term emission, variability and inter-band correlations have been evaluated. The spectral evolution will also be discussed and interpreted. The broadband emission was reproduced in the framework of different emission models for each activity level, studying the evolution of the physical parameters describing the emission of this source and the observed characteristics of its emission.

Speaker: Jorge Otero-Santos (Instituto de Astrofisica de Canarias)

ID321-10_years_of_1ES0647+250.pdf

16:15 Neutral pion bumps in TeV spectra of X-ray flaring blazars

Very high-energy (VHE, $E > 100$ GeV) observations of blazar Mrk 501 with MAGIC in 2014 have revealed an unusual narrow spectral feature at ~3 TeV during an extreme X-ray flaring activity. The one-zone synchrotron-self Compton scenario, widely used in blazar broadband spectral modeling, fails to explain the narrow TeV component. Motivated by this rare observation, we propose an alternative model where narrow features in VHE blazar spectra result from the decay of neutral pions ($\pi^0$ bumps). These are in turn produced by interactions of protons with hard X-ray photons ($>50$ keV) whose number density can increase during flares. No $\pi^0$ bumps are predicted in X-ray "quiescense", as the proton energy is not high enough to exceed the threshold for pion production. We explore the physical conditions needed for the emergence of narrow $\pi^0$ bumps in blazar VHE spectra and discuss their detectability with the Cherenkov Telescope Array.

Speaker: Maria Petropoulou (NKUA)

Gamma2022_Petropoulou

Gamma2022_Petropoulou

Gamma2022_Petropoulou.pptx

15:00 → 16:30 Contributed Talks: GAL parallel 1 (Aula Magna Biologia) Chair: Martina Cardillo

15:00 MAGIC observations of the putative PeVatron SNR G106.3+2.7 in the proximity of the Boomerang PWN

MAGIC observations of the putative PeVatron SNR G106.3+2.7 in the proximity of the Boomerang PWN.
The supernova remnant SNR G106.3+2.7 in the proximity of the Boomerang PWN has recently gained a lot of attention due to the emission above 100 TeV detected by HAWC, Tibet AS\gamma, and LHAASO. This SNR shows a characteristic comet-like morphology in radio observations, with a head and a tail. Due to the limited angular resolution of air shower experiments, it is not clear if the emission comes from the head, where an energetic pulsar wind nebula is located, or from the tail, where a clump of molecular cloud is present. The MAGIC telescopes, with an angular resolution better than 0.1 degrees, observed G106.3+2.7 for 122 hours and found a significant gamma-ray excess elongated along the axis of the comet shape. We performed a spectro-morphological analysis, and found the spectrum of the tail to be harder than the one in the head. This suggests that the 100 TeV emission detected by air shower experiments is from the tail. The multiwavelength spectrum of the tail emission favors proton acceleration up to energies of ~1 PeV, while the emission mechanism of the head could be both hadronic or leptonic.

Speaker: Takayuki Saito

V2_Gamma2022BoomerangTSaito.pdf

15:15 Revisiting HESS J1809–193 — a very-high-energy gamma-ray source in a fascinating environment

HESS J1809–193 is one of the unidentified very-high-energy gamma-ray sources in the H.E.S.S. Galactic Plane Survey (HGPS). It is located in a rich environment, with an energetic pulsar and associated X-ray pulsar wind nebula, several supernova remnants, and molecular clouds in the vicinity. Furthermore, HESS J1809–193 was recently detected at energies above 56 TeV with HAWC, which makes it a candidate for a PeVatron, i.e., a source capable of accelerating cosmic rays up to PeV energies.
We present a new analysis of the TeV gamma-ray emission of HESS J1809–193 with H.E.S.S., based on improved analysis techniques. We find that the emission is best described by two components with distinct morphologies and energy spectra. We complement this study with an analysis of Fermi-LAT data in the same region. Finally, taking into account also further multi-wavelength data, we interpret our results both in a hadronic and leptonic framework.

Speaker: Lars Mohrmann (Max Planck Institute for Nuclear Physics, Heidelberg)

ID326-LarsMohrmann-HESSJ1809.pdf

15:30 Constraining leptonic emission scenarios for the PeVatron candidate HESS J1702-420 with deep XMM-Newton observations

The unidentified TeV source HESS J1702-420 has recently been proposed as a new hadronic PeVatron candidate, based on the discovery of a small-scale emission sub-region with extremely hard gamma-ray spectrum up to 100 TeV (named HESS J1702-420A). Given the difficulty to discriminate between a hadronic or leptonic origin of the TeV emission, based on the H.E.S.S. measurement alone, we opted for a multi-wavelength approach. A deep X-ray observation was carried out using the XMM-Newton satellite, with the goal of probing a possible association with a hidden leptonic accelerator. No evidence of a clear counterpart for HESS J1702-420A was found in the X-ray data. After excluding an association with all nearby X-ray point sources, we derived a strict upper limit on the average magnetic field in the HESS J1702-420A region, which significantly strengthen its classification as a hadronic PeVatron candidate. We additionally report the serendipitous discovery of a new possibly extended X-ray source, whose association with HESS J1702-420A is deemed unlikely but cannot be completely ruled out.

Speaker: Luca Giunti

ID324_LucaGiunti_HESSJ1702-420_seen_by_XMM.pdf

15:45 HESS J1831-098: a hadronic PeVatron or a very energetic pulsar wind nebula?

We will present the detection, spectral and morphological characterization of HESS J1831-098 with H.E.S.S. The source was previously identified as a hotspot in the H.E.S.S. Galactic Plane Survey catalogue. The hard power-law spectrum extends with an index of ~2.1 up to >30 TeV with no indication for a cut-off, making HESS J1831-098 an interesting PeVatron candidate. The HAWC point source 3HWC J1831-095 is located in the vicinity of HESS J1831-098 and has similar spectral properties, supporting the hypothesis of an association of these two objects. We will discuss the origin of the VHE gamma-ray emission of HESS J1831-098 in the context of a possible association with the powerful pulsar PSR J1831-0952 or with a dense molecular cloud illuminated by energetic particles escaped from a nearby SNR. In both scenarios, the hard spectrum of this H.E.S.S. source clearly testifies to the presence of an extreme particle accelerator, possibly a PeVatron.

Speaker: Iryna Lypova (LSW)

id425_lypova_hess_j1831_v1.pdf

16:00 The jets of SS 433 as seen by HESS

The microquasar SS 433 is the only known compact binary system in which accretion is believed to occur in the super-Eddington regime. This leads to the launching of two persistent, semi-relativistic jets that extend from the binary, almost perpendicular to the line of sight. X-ray observations reveal that these jets extend out to around 100 pc on either side of the central system, terminating at the radio structure W50. The jets of SS 433 were recently reported to be a source of TeV gamma-rays by the HAWC collaboration. We report here the result of deep observations of this system with the H.E.S.S. array of telescopes, resulting in the first detection of the system by an Imaging Atmospheric Cherenkov Telescope array. The superior energy and angular resolution of the H.E.S.S. array allow for a detailed study of the morphology and spectral energy distribution of the gamma-ray emission in the jets. This information can be used to constrain parameters of the jet dynamics, as well as provide information on the particle acceleration taking place in the jets.

Speaker: Laura Olivera Nieto (Max Planck Institut fur Kernphysik MPIK)

ID382_OliveraNieto_SS433.pdf

16:15 A hard X-ray look at the Manatee nebula (W50) powered by the Galactic microquasar SS 433

W50/SS433 is a complex and fascinating system that represents an important test bed for many astrophysical processes. Powered by the microquasar SS 433, the W50 nebula — classified as a supernova remnant with an unusual double-lobed morphology similar to a Manatee — has been proposed to be a Galactic PeVatron candidate; a scenario that has been recently revived with the detection of very high energy TeV emission with HAWC. We present the first NuSTAR and XMM-Newton observations of the inner eastern lobe of W50, combined with archival Chandra and XMM-Newton observations spanning various regions across the eastern lobe. We resolve and characterize hard non-thermal X-ray emission detected up to 30 keV, originating from a knotty, few-arcminute size, head region located ~29 pc east of SS 433, and constrain its photon index to 1.58+/-0.05 (0.5-30 keV). The index gradually steepens away from SS 433 and all the way out to the radio ear (at ~96 pc east of SS 433) where soft thermal X-ray emission dominates. The unusually hard index and blobby structure seen from the `head' of the eastern jet is similar to what is observed in pulsar wind nebulae as well as in extragalactic AGN jets, and challenges classical particle acceleration processes. We conclude with an outlook on upcoming and future modelling and observational studies of this system that continues to puzzle and fascinate a diverse range of researchers even more than 40 years into its discovery.

Speaker: Samar Safi-harb (University of Manitoba)

safi-harb-gamma2022-manatee-withbuilds.pdf

16:30 → 17:00 coffee break

17:00 → 18:30 Contributed Talks: EGAL parallel 2 (Aula Magna Ciències de la Terra) Chair: Frederic Daigne

17:00 An unbiased search for TeV emission from high-frequency peaked BL Lacs

High-frequency-peaked BL Lacs (HBLs) dominate the extragalactic TeV sky, with more than 50 objects detected with the current generation of ground-based TeV gamma-ray observatories. In the last three years, the VERITAS telescope array has observed a flux-limited sample of 36 X-ray selected HBLs with the goal of producing the first unbiased census of TeV emission from HBL blazars. The VERITAS HBL sample contains known TeV sources as well as 15 objects for which TeV emission has not been reported before. The results of this VERITAS campaign include the detection of new TeV blazars as well as unbiased estimates of the TeV flux of HBLs that have previously been reported only during flaring states. The implications of our results in understanding the intrinsic properties of HBLs as a source population will be discussed.

Speaker: Manel Errando (Washington University in St Louis)

ID414-Errando-VERITAS_blazar_survey.pdf

17:15 Characterizing the VHE emission of the extreme HBLs 1ES 1218+304 and 1ES 0229+200 with VERITAS

The modelling of the spectral energy distribution (SED) of some high-frequency peaked BL Lac objects (HBLs) has proved challenging for the so-called extreme candidates, which can have their TeV peak at energies $> 1$ TeV and a hard intrinsic TeV spectrum of $\Gamma < 2$. The HBLs 1ES 1218+304 ($z = 0.182$) and 1ES 0229+200 ($z = 0.1396$) are two characteristic examples. Historically, leptonic one-zone synchrotron self-Compton (SSC) models have been used when modelling the broadband SED of BL Lac objects with relative success, but they fail to fully describe the emission of their extreme counterparts without requiring unexpectedly large or small physical quantities, or reaching far beyond the equipartition condition, when accounting for extragalactic background light (EBL).
In this work, using archival VERITAS data from 2008 to 2021 on 1ES 1218+304 and 1ES 0229+200 combined with data from the Swift-XRT and Fermi-LAT observatories for extended wavelength coverage, we provide an updated look on the modelling of extreme HBLs.

Speaker: Pedro Batista on behalf of the VERITAS collaboration (Deutsches Elektronen-Synchrotron (DESY/Zeuthen))

PedroBatista_Gamma22.pdf

17:30 The peculiar short-duration GRB 200826A and its supernova

Short Gamma-ray burst (sGRBa) are linked to the merger of compact objects. However the GRB 200826A is peculiar because by definition it was a SGRB, with a rest-frame duration of ∼ 0.5 s, but this event was energetic and soft, which is consistent with long GRBs (LGRBs) associated with the end states of very massive stars. The relatively low redshift (z=0.75) motivated a multi-wavelength follow-up campaign to understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) imaging in adaptive optics, coupled with optical imaging and spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution is in agreement with several LGRB-SNe. It is not compatible with both theoretical models of kilonovae (KNe) and with AT2017gfo, the KNa associated with the gravitational wave signal GW 170817. Analysis of the prompt GRB shows that this event follows the Amati relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical for LGRBs, but with one of the highest specific star-formation rates. We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs.
ADS link: https://ui.adsabs.harvard.edu/abs/2021arXiv210503829R/abstract

Speaker: Andrea Rossi (INAF - Osservatorio di Astrofisica e Scienza dello Spazio)

ID274-AndreaRossi-GRB200826A.pdf

The peculiar short-duration GRB 200826A and its supernova

17:45 Intergalactic magnetic field studies by means of the gamma-ray emission from GRB 190114C

The origin of the large-scale magnetic fields in the Universe is one of the long-standing problem in cosmology. To discriminate among the different explanations it is crucial to measure the intergalactic magnetic field (IGMF) in the voids among the galaxies. Gamma-rays coming from extragalactic sources can be used to constrain the IGMF due to their interaction with the intergalactic medium. Particularly, strong transients allow to constrain very weak IGMFs. We use CRPropa3 to propagate the measured very-high energy (E > 100 GeV) spectrum from GRB 190114C in the intergalactic medium. We then compute the expected cascade emission in the GeV domain for different IGMF settings and compare it with the Fermi/LAT limits for different exposure times.

Speaker: Paolo Da Vela (University of Innsbruck)

ID358-PaoloDaVela_GRB_and_IGMF.pdf

18:00 Perspectives of observing prompt very-high-energy gamma emission from binary neutron star mergers

The prompt emission in Gamma-ray bursts is usually observed 10 keV-10 MeV range. However, to date, at higher energies, it has not been detected yet. Although the current generation very-high-energy (VHE; E > 30 GeV) gamma-ray detectors (MAGIC and H.E.S.S.)  have successfully demonstrated the capability of detection of the afterglow of GRB, the prompt phase of detection has remained unexplored. Here, we investigate the perspectives of multi-messenger observations to detect the prompt emission of short GRBs at very-high-energies. Considering binary neutron star merger as progenitor of short GRBs, we evaluate the joint detection efficiency of the Cherenkov Telescope Array observing in synergy with the third generation of gravitational wave detectors, such as the Einstein Telescope and Cosmic Explorer. We evaluate  taking the expected capabilities to detect and localize gravitational wave events in the inspiral phase and to provide an early warning alert able to drive the VHE detection. We demonstrate that the sensitivities of CTA make it possible the detection of the VHE emission even if it is several orders fainter than the one observed at 10 keV–10 MeV. We discuss the results in terms of possible scenarios of prompt VHE counterparts of binary neutron star mergers, such as the synchrotron self Compton components in the leptonic GRB model, high energy tail of the hadronic GRB model, and external Inverse Compton emission.

Speaker: Biswajit Banerjee (Gran Sasso Science Institute, Viale F. Crispi 7, I-67100, LAquila (AQ), Italy)

Gamma_2022_20220704_banerjee.pdf

18:15 GRB prompt emission from the synchrotron radiation of relativistic electrons in a decaying magnetic field

The parameters of observed prompt gamma-ray burst spectra provide the key constraint for the proposed emission models. The low energy slope of the photon spectrum depends on the involved emission process, and observations show that it is often not consistent with the simple assumptions of the synchrotron model. We studied the effect of the synchrotron cooling of relativistic electrons in a decaying magnetic field on the spectrum. The numerical simulations of the emitted spectrum in the comoving frame performed for a large parameter space will be presented, and the derived low energy spectral slopes will be discussed.

Speaker: Željka Bošnjak (University of Zagreb)

17:00 → 18:30 Contributed Talks: GAL parallel 2 (Aula Magna Biologia) Chair: Kathrin Egberts

17:00 The Galactic diffuse gamma-ray emission meets the PeV frontier

The Tibet ASγ and LHAASO collaborations recently provided the first evidence of a diffuse γ-ray emission in the Galaxy up to the PeV from the Galactic plane. Due to the challenges this imposes to current theoretical models it is crucial to carefully study different scenarios of diffuse γ-ray production, specially towards the centre of the Galaxy. In particular, the current models of diffuse emissions struggle to reproduce ASγ and LHAASO data.
In this contribution, we show that these measurements seem to favour an inhomogeneous transport of cosmic rays throughout the Galaxy, specially motivated by the measurements of the Fermi-LAT detector. Moreover, we discuss the relevance of non-uniform cosmic-ray transport scenarios and the implications of these results for cosmic-ray physics and show that the energy spectra measured by Tibet ASγ, LHAASO, ARGO-YBJ and Fermi-LAT in several regions of the sky can be consistently described in terms of the emission arising by the Galactic cosmic-ray ``sea''. We also comment on the impact of other possible contributions, as the γ-ray emission from TeV halos or unresolved sources.

Speaker: Pedro De la Torre Luque (Oskar Klein Centre, Stockholm University)

ID374-DeLaTorre_Galactic_Diffuse.pdf

17:15 New insights towards the Galactic center from HESS

The Galactic center is one of the richest region in the Galaxy harboring the supermassive black hole Sagittarius A* surrounded by the Central Molecular Zone (CMZ), several supernova remnants, pulsars wind nebulae (PWNe), and star forming regions. TeV emission was revealed from individual sources (HESS J1745-290, the PWN G0.9+0.1, HESS J1746-285) and from the CMZ itself. In the CMZ the emission likely originates from cosmic rays pervading the Galactic center region and interacting with the dense gas. We present the first 3D analysis of the Galactic center region using 12 years of H.E.S.S. data and the Gammapy open-source analysis package. This analysis allows to extract for the first time, using a common field-of-view source modeling, the intrinsic spectra of the known H.E.S.S. sources HESS J1745-290, the PWN G0.9+0.1, HESS J1746-285 and HESS J1741-302.

Speaker: Justine Devin (CNRS - LUPM)

ID461-JustineDevin-Galactic_Center_region_with_HESS.pdf

17:30 The origin of MeV gamma-ray diffuse emission from the inner Galactic region

The origin of the inner Galactic emission, measured by COMPTEL with a flux of 0.01 MeV/cm$^2$/s/sr in the 1-30 MeV range from a region of |l|<60 degree and |b|<10 degree, has remained unsettled since its discovery in 1994. We investigate the origin of this emission by taking into account the Galactic diffuse emission and individual sources which are not resolved by COMPTEL. The Galactic diffuse emission is calculated by GALPROP to reconcile the cosmic-ray and gamma-ray spectra with observations by AMS-02, Voyager, and Fermi-LAT, resulting in a flux of 20-80% of the COMPTEL emission. The source contribution is estimated for sources cross-matched between the Swift-BAT and Fermi-LAT catalogs by extrapolating the energy spectra in the hard X-ray and GeV gamma-ray ranges, resulting in a flux of at least 10% of the COMPTEL excess. We will give the details of the analysis and show that the COMPTEL emission could be reproduced by a combination of the Galactic diffuse emission, resolved sources, and likely the gamma-ray cosmic background. We will also report on the importance of future missions for MeV gamma-ray observations, which would be critical for bridging the "MeV gap" in the spectra of gamma-ray sources.

Speaker: Naomi Tsuji (Kanagawa University)

NaomiTsuji_COMPTEL_excess.pdf

17:45 Assessing the Impact of Hydrogen Absorption on the Characteristics of the Galactic Center Excess

We present a new reconstruction of the distribution of atomic hydrogen in the inner Galaxy that is based on explicit radiation-transport modelling of line and continuum emission and a gas-flow model in the barred Galaxy that provides distance resolution for lines of sight toward the Galactic Center. The main benefits of the new gas model are, a), the ability to reproduce the negative line signals seen with the H$I$4PI survey and, b), the accounting for gas that primarily manifests itself through absorption.

We apply the new model of Galactic atomic hydrogen to an analysis of the diffuse gamma-ray emission from the inner Galaxy, for which an excess at a few GeV was reported that may be related to dark matter. We find with high significance an improved fit to the diffuse gamma-ray emission observed with the Fermi-LAT, if our new H$I$ model is used to estimate the cosmic-ray induced diffuse gamma-ray emission. The fit still requires a nuclear bulge at high significance. Once this is included there is no evidence for a dark-matter signal, be it cuspy or cored. But an additional
so-called boxy bulge is still favoured by the data.
This finding is robust under the variation of various parameters, for example the excitation temperature of atomic hydrogen, and a number of tests for systematic issues.

Speaker: Martin Pohl (Uni Potsdam / DESY)

ID224-MartinPohl-GC_excess.pdf

18:00 Gamma-ray observations of nearby HII regions

I present the analysis of the Fermi-LAT data in the region of the Vela Molecular Cloud Ridge (VMR). The latter is a dense region of gas located at approximately 1 kpc from us and it is the closest region that hosts intermediate-mass- and massive-star formation. Associations of massive stars have been proven to be powerful particle accelerators and are consequently expected to be bright gamma-ray sources. However, the gamma-ray emission associated with these sources is often of controversial origin, due to the superposition of multiple sources. Massive stars can be traced by observations of their surrounding HII regions. The latter are regions of gas which is ionized due to the strong radiation fields of the stars themselves. HII regions are identified by infrared observations and several of them have been recognized within the VMR. For the first time, we detected high-energy emission spatially coinciding with a few of these HII regions, which leaves no doubt about the identification of gamma-ray emission with massive stars. I will present the result of the morphological and spectral analysis of these sources and I will discuss the origin of their emission and their possible contribution to the large-scale diffuse emission.

Speaker: Giada Peron (Max-Planck-Institut für Kernphysik, Hedielberg, Germany)

ID394_Peron_Giada_HIIregions.pdf

18:15 NuSTAR broad-band X-ray observations and multi-wavelength investigations of Galactic TeV sources

We will report recent progress on the NuSTAR observations of a variety of Galactic TeV sources including PeVatron candidates. Given its sub-arcminute angular resolution and high sensitivity above 10 keV, NuSTAR's hard X-ray morphology and spectroscopy data allow us to probe sub-PeV electron populations through detecting synchrotron X-ray radiation. NuSTAR, along with other X-ray telescopes, play an important and complementary role to the ultra-high energy (> 100 TeV) gamma-ray telescopes. Our targets include 8 middle-aged pulsar wind nebulae, W50 lobes powered by the microquasar SS433, and a few other gamma-ray sources detected by HAWC, LHAASO and VERITAS. Combined with radio, GeV and TeV data, we aim to provide a complete, multi-wavelength view of the most energetic particle accelerators in our galaxy. In this presentation, we will review our observation campaign, highlight some key results and discuss our future plan of observing other sources such as Westerlund 2 and Cassiopeia A.

Speaker: Kaya Mori (Columbia Astrophysics Laboratory)

ID411_KMori_NuSTAR.pdf

18:30 → 21:00 Welcome Reception

Tuesday 5 July

09:30 → 11:00 Review Talks: Tuesday (Aula Magna Biologia) Chair: Martin Lemoine

09:30 Cosmic Rays and Neutrinos at the Highest Energies

Ultrahigh energy cosmic rays (UHECRs), i.e., cosmic rays with energies above 10^18 eV (=1 EeV), are the most energetic particles ever observed. Their sources are still a mystery. Giant ground-based observatories, such as the Pierre Auger Observatory and the Telescope Array, have shown that the sources of UHECRs are extragalactic. The observed UHECR spectrum has subtle features that can be explained by a combination of interactions with cosmic backgrounds, a changing composition of the primaries, and a maximum acceleration energy of the dominant sources. Hints of anisotropies begin to appear at energies above tens of EeV, just when statistics become very limited. We review the progress over the last decade of UHECR observations, the implication for the neutrino and photon counterparts, and the future outlook for discovering the origin of UHECRs.

Speaker: Angela Olinto

#302_AngelaOlinto_UHECRs.pdf

10:15 Dark Matter Searches with Gamma Rays and Cosmic Rays

The existence of dark matter - the dominant, non-baryonic, neutral and cold matter component of our Universe - is inferred from its gravitational effects at galactic and cosmological scales, as well as from the power spectrum of the temperature anisotropies of the cosmic microwave background. Several theoretically plausible dark matter candidates, such as WIMPs, axions or primordial black holes, would produce distinct spectral and/or morphological signatures in the measured fluxes of different cosmic ray species. Thus, identification of such signatures (a procedure known as "indirect" dark matter detection) could help pinpoint the nature of dark matter. In this talk, I will review several of the existing experimental methods aimed at indirect detection of dark matter signatures, as well as the latest results in the field.

Speaker: Javier Rico (IFAE-BIST)

DM_Gamma_CR_JRico.pdf

11:00 → 11:30 coffee break

11:30 → 12:20 Highlight Talks topical: Tuesday (Aula Magna Biologia) Chair: Sabrina Casanova

11:30 Particle acceleration and gamma-ray emission from starburst galaxies

The intense star-forming activity typical of starburst galaxies results in unique conditions for high-energy particles. The enhanced supernova rate associated with such star formation can in fact transfer a large amount of power to non-thermal particles which, in turn, can lose most of their energy in the dense and perturbed starburst environment before being able to escape it.
I will discuss the transport conditions in starburst galaxies and their multimessenger implications in terms of gamma rays and high-energy neutrinos.
The starburst activity can also launch and sustain powerful galactic wind bubbles extending for several kiloparsecs. I will illustrate how particles can be accelerated up to hundreds of PeV at shocks produced in such winds and I will highlight the associated high-energy radiation.
Finally, by taking into account the star formation history of the Universe, I will assess the potential contribution of starburst galaxies to the observed diffuse flux of gamma rays, high-energy neutrinos and cosmic rays at energies beyond the Knee.

Speaker: Enrico Peretti (Niels Bohr Institute)

ID505_PerettiEnrico_Starburst.pdf

11:55 Stellar Clusters as Pevatron Candidates

Massive stars blow powerful winds and eventually explode as supernovae. By doing so, they inject energy and momentum in the circumstellar medium, which is pushed away from the star and piles up to form a dense and expanding shell of gas. The effect is larger when many massive stars are grouped together in bound clusters or associations. Large cavities form around clusters as a result of the stellar feedback on the ambient medium. They are called superbubbles and are characterised by the presence of turbulent and supersonic gas motions. This makes star clusters ideal environments for particle acceleration, and potential contributors to the observed Galactic cosmic ray intensity.

Speaker: Stefano Gabici (APC)

gabici.pdf

12:20 → 13:10 Highlight Talks observational: Tuesday (Aula Magna Biologia) Chair: Sabrina Casanova

12:20 Highlights from VERITAS

VERITAS is one of the world’s most sensitive detectors of astrophysical VHE (E > 100 GeV) gamma rays. This array of four 12-m imaging atmospheric Cherenkov telescopes, located in southern Arizona, USA, has operated for ~15 years. VERITAS science spans Galactic topics, including pulsar wind nebulae, binary systems, and supernova remnants; extra-galactic topics, including studies of blazars and radio galaxies, searches for gamma-ray bursts and fast radio bursts; multi-messenger science; and astroparticle physics topics including searches for dark matter. VERITAS has also pioneered the use of IACTs for optical astronomy, particularly via intensity interferometry. Recent highlights from the VERITAS observing program and scientific results will be presented.

Speaker: John Quinn (University College Dublin)

ID510-JohnQuinn-VERITAS-Highlights-Gamma2022.key

ID510-JohnQuinn-VERITAS-Highlights-Gamma2022.pdf

ID510-JohnQuinn-VERITAS-Highlights.pdf

12:45 Highlights from HAWC

The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory in the high mountains of Mexico is giving us a new view of the TeV sky. HAWC operates 24hrs/day with over a 95% on-time and observes the entire overhead sky (~8sr over the course of the day). HAWC has accumulated more seven years of data and has recently completed our “Pass 5” re-analysis giving us significant improvements in our low energy response, angular resolution, background rejection and an expanded field of view. This talk will present an overview of these recent HAWC results showing our updated sky catalog, our view of the highest energy gamma-ray sky (including sources above 50 and 100 TeV), long-term monitoring of nearby AGN and recent observations of galactic Pevatrons. In addition, we will present recent limits on primordial black holes, Lorentz invariance violation and multi-messenger observations, as well as comparisons of HAWC and IACT measurements.

Speaker: Jordan Goodman (University of Maryland)

Goodman Barcelona 2022.key

Goodman Barcelona 2022.pdf

13:10 → 15:00 lunch break

15:00 → 16:30 Contributed Talks: EGAL parallel 3 (Aula Magna Ciències de la Terra) Chair: Simone Mender

15:00 A multiwavelength look at the 2017 flare of OJ 287

Intermediate blazars (IBLs and LBLs) are known to present complex multiwavelength SEDs and variabilities, often requiring an interpretation beyond standard one-zone emission models. OJ 287 is the archetype of such a complex blazar. On top of hosting a binary supermassive black hole system, it presents multiple other unusual features like an extended X-ray jet, possible jet precession, mixed observed radio jet kinematics, and complex flares. We focus our attention on a peak of activity in Feb 2017, where OJ 287 displayed a soft X-ray flare with relatively minor counterparts in other wavelengths. We study the multiwavelength behavior of the source before, during, and after the flare with data in optical, UV, X-ray, gamma-ray, and for the first time, data from a very-high-energy detection above 100 GeV with VERITAS. Based on the discovery of a radio jet ejecta emerging from the core at the same period, we present a scenario in which a compact emission zone moves through the powerful emission of the core that can accurately depict the multiwavelength SED at different periods. This scenario will be discussed in the broader context of the characterization of the intermediate blazars.

Speaker: Olivier Hervet (UCSC)

2022_07_Gamma2022_OJ287_Hervet_v3.pdf

Animation of Orbiting Black Holes in Galaxy OJ 287 - YouTub.webm

15:15 Non-thermal radiation from super-Eddington winds in AGNs

Accretion onto supermassive black holes can proceed in different regimes. When the accretion rate significantly exceeds the Eddington limit, the innermost part of the disk inflates as the radiation pressure becomes dominant and important mass loss in the form of a radiation-driven wind occurs. We will present the results of an investigation of the effects of these winds on clouds of the broad line region that surrounds the supermassive black hole in some Active Galactic Nuclei. Non-thermal radiation is produced by particles locally accelerated in the bow shocks formed around the clouds. The radio emission so generated can explain the detection of synchrotron radiation in non-jetted and usually radio quiet Seyfert galaxies.

Speaker: Gustavo E. Romero (Instituto Argentino de Radioastronomía (IAR))

521_Romero Gustavo_Radiation from AGN winds.pdf

521_Romero Gustavo_radiation from radio silent AGNs.key

15:30 The January 2017 Orphan Gamma-ray Flare from the Radio Galaxy NGC 1275: VERITAS and Multiwavelength Results

NGC 1275 (3C84) is an active galactic nucleus (AGN) corresponding to the brightest cluster galaxy in the nearby Perseus supercluster of galaxies. As such, it has been the focus of intense study and monitoring across all wavebands for several decades. In 2010, it became one of the rare radio galaxies detected in very-high-energy gamma-ray emission (VHE;>100 GeV) with a reported flux by the MAGIC observatory of ~2.5% of the Crab Nebula and a soft energy spectrum with photon index of ~4. Since this discovery, the VERITAS observatory has monitored NGC 1275 every year. This presentation will describe the results of this long-term monitoring program with a particular focus on the extreme VHE flare displayed by NGC 1275 in early January 2017. Alerted by MAGIC on January 1, 2017 with a detection of NGC 1275 at a flux of ~150% Crab, VERITAS followed with observations on January 2, and 3, 2017 with the source still in a high state (65% Crab) but declining. Using data from radio, optical, X-ray and high-energy (HE) gamma rays, we will show the most complete simultaneous multiwavelength spectral energy distribution (SED) of the source for both the nights of January 1, and 2, 2017. It appears that the source was only flaring in gamma-rays – this 'orphan flare' condition strongly challenges standard emission scenarios. We present an emission model where the multiwavelength SED can be accurately depicted considering two interacting emitting zones at a few parsecs downstream from the core. The comparison of this scenario with other emission models proposed for NGC 1275, as well as the outstanding issues of TeV flares in radio galaxies are discussed.

Speaker: Lucy Fortson (University of Minnesota)

ID440-LucyFortson-VERITAS_NGC1275.pdf

15:45 The most complete multi-wavelength view of M87 to date: the 2017 campaign

In 2017, the Event Horizon Telescope (EHT) Collaboration successfully imaged the black hole at the center of the M87 galaxy. At the same time, an extensive multi-wavelength campaign was conducted involving ground and space-born instruments to cover energies from radio to very-high energy (VHE) gamma rays. We found that the core of M87 and the innermost knot HST-1 are in historically low states. In terms of X-ray energies, the core flux dominates over HST-1. We present the most extensive quasi-simultaneous spectral energy distribution (SED) and discuss the challenges of combining data with vastly different spatial resolutions. By modeling the broadband spectrum with two different types of single-zone leptonic models, we can infer that the low-state gamma-ray emission via inverse Compton must originate from a different region than the millimeter-band emission. We conclude that the gamma rays can only be generated in the inner jet if there are strongly particle-dominated regions upstream of HST-1. Our collected data has been made open access, and we encourage the application of structured jet models on these data.

Speaker: Alexander Hahn (Max Planck Institute for Physics)

ID449_Hahn_MWL_M87_2017.pdf

16:00 FSRQ or BL Lac? MWL view of the transitional blazar OT081

We report on a multiwavelength study of the blazar OT081 during a high-activity state in July 2016, in which very-high-energy (VHE; E >100 GeV) gamma-ray emission from the source was discovered by MAGIC and H.E.S.S. telescopes, following a trigger from Fermi-LAT. OT081 is a luminous blazar well known for its variability in many energy bands, but only once detected in the VHE energy range. The presence of broad emission lines in the optical spectrum of the source challenges the categorization of OT081 as a BL Lac and hints at its transitional nature between a BL Lac and a flat spectrum radio quasar.
From the analysis of the multiwavelength light curves and of the broadband spectral energy distribution (SED), we study the evolution of the source, and identify four states of activity in the period 6 July -- 20 August 2016. Instruments and facilities involved in this work are H.E.S.S., MAGIC, Fermi-LAT, Swift-XRT, Swift-UVOT, Lick/KAIT, ATOM, AZT-8+ST7, ALMA, Metsahovi, OVRO, RINGO, Steward Observatory, Tuorla Observatory, and the WEBT community. Moreover a dedicated study with the Very Long Baseline Array at 43GHz has provided key insight regarding the jet evolution. A simple one-zone synchrotron self-Compton model is not sufficient to describe the broadband SED, and external Compton is required to explain the high Compton dominance displayed by the source. We present the MWL study and the modeling, with our interpretation of the emission
mechanism, and compare our findings with the other few transitional blazars discovered so far.

Speaker: Marina Manganaro (University of Rijeka, Department of Physics)

OT 081 discovery in VHE gamma rays for Gamma 2022_plusGPP.pdf

16:15 Probe AGNs variability with the Cerenkov Telescope Array

Relativistic jets launched by blazars are among the most powerful particle accelerators in the Universe. The emission over the entire electromagnetic spectrum of these relativistic jets can be extremely variable with scales of variability from less than few minutes up to several years. These variability patterns, which can be very complex, contain information about the acceleration processes of the particles and the area(s) of emission. Thanks to its sensitivity, five-to twenty-times better than the current generation of Imaging Atmospheric Cherenkov Telescopes depending on energy, CTA will be able to follow the emission from these objects with a very accurate time sampling and over a wide spectral coverage from 20 GeV to 300 TeV and thus reveal the nature of the acceleration processes at work in these objects. We will show the first results of our lightcurve simulations and long-term behavior of blazars as will be observed by CTA, based on state-of-art particle acceleration models.

Speaker: Floriane Cangemi (CNRS/IN2P3/LPNHE)

FlorianeCangemi-AGNvariability.key

FlorianeCangemi-AGNvariability.pdf

15:00 → 16:30 Contributed Talks: GAL parallel 3 (Aula Magna Biologia) Chair: Jakub Jurysek

15:00 Can massive star clusters produce PeV photons?

The LHAASO observatory recently detected a PeV photon in the direction of the Cygnus X star-forming region. A plausible origin for this emission is the association of massive stars Cygnus OB2. This raises the question whether or not massive star clusters can accelerate particles to ultra-high energies. Clustered stars heat their surrounding medium, which inflates a cavity filled with multiple shocks, strong turbulence and amplified magnetic fields. Although these are ideal conditions for particle acceleration, it is yet unclear how the different acceleration processes can act collectively to produce ultra-high energy particles.

In this work we show that even though the maximum energy of the particles accelerated in these environments is expected to be higher than in the case of isolated massive stars or supernova remnants, it is not straightforward to account for an UHE gamma-ray emission. Amongst several possibilities of acceleration mechanisms, including embedded supernova remnants, wind termination shocks or large-scale turbulent waves, a promising scenario is that of a fast supernova shock expanding in the cold wind around compact clusters. In this case, protons could be accelerated up to 10 PeV and beyond, and subsequently interact to produce PeV photons.

Speaker: Thibault Vieu (Max-Planck-Institut für Kernphysik, Heidelberg)

ID424-ThibaultVieu_Massive_star_clusters.pdf

15:15 Cygnus OB2 as testing ground for particle acceleration at the wind termination shock of massive star clusters

In the last decade, the detection by diverse experiments of diffuse gamma-ray emissions toward several galactic massive star clusters has renewed the attention to these objects as potential galactic cosmic ray accelerators. Indeed, the conversion of a few percent of the power supplied by the strong winds from the massive stars into accelerated particles is enough to explain the observed gamma-ray luminosities in a pure hadronic scenario. Cygnus OB2 is one of the massive star clusters found in coincidence with diffuse gamma-ray emission detected in a broad range of energies, from a few GeV up to 1.4 PeV.
In this work, we aim to compare the morphological and spectral features of the observed gamma emission with those predicted from a theoretical model where particles are accelerated at the termination shock of the cluster wind. Both the expected gamma-ray morphology and spectrum depend on the properties of the distribution of accelerated cosmic rays, which are directly affected by the physics of acceleration at the termination shock and by the propagation in the hot expanding bubble created by the cluster wind.
We found our model to be in good agreement with the observed spectral energy distribution. The expected radial gamma-ray profile reproduces fairly well HAWC observations but is not totally in accord with Fermi results. According to the best fit model, Cygnus OB2 should be able to accelerate cosmic rays up to 1 PeV, hence resulting in a likely cosmic ray PeVatron.

Speaker: Stefano Menchiari (University of Siena)

StefanoMenchiari-CygOB2-Gamma2022.pdf

15:30 New cosmic-ray acceleration sites detected by the Fermi-LAT in our Galaxy

Cosmic rays are mostly composed by protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions which in turn decay into gamma rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum was detected in the gamma-ray spectra of four Supernovae Remnants (SNRs), IC 443, W44, W49B and W51C, with the Fermi Large Area Telescope. This detection provided direct evidence that cosmic-ray protons are (re-)accelerated in SNRs.

In this review, we present the results from a comprehensive search for low energy spectral breaks. We use 8 years of data from the Fermi Large Area Telescope between 50 MeV and 1 GeV. This search is based on the 4FGL catalog from which we extracted the unidentified sources or those associated to SNRs with a significance above 3 sigma at low energy in both cases. Several SNRs, binaries and one star forming region as well as a handful of unidentified sources are detected with our search.
These best candidates will be presented, focusing on the most intriguing cases such as Eta Carinae and the Cygnus star forming region, thus enlarging our view to potential new cosmic-ray acceleration sites.

Speaker: Marianne Lemoine-Goumard (LP2I Bordeaux)

ID271_LemoineGoumard_PionBump.pdf

15:45 Cosmic Rays origin studies in the W 44 region with Fermi-LAT and MAGIC observations

W 44 is a well-known Supernova Remnant (SNR) observed in high-energy gamma-rays, widely studied to investigate cosmic ray (CR) acceleration. Several analyses of the W 44 surroundings showed the presence of a gamma-ray emission offset from the radio SNR shell. This emission is thought to originate from escaped high-energy CRs.

We present a detailed analysis of the W 44 region as seen by Fermi-LAT, focusing on the spatial and spectral characteristics of both W 44 SNR and its surroundings. The spatial analysis was limited to energies above 1 GeV in order to exploit the improved angular resolution of the instrument, deriving a detailed description of the region morphology. The spectral analysis was extended down to 100 MeV, favouring the hadronic origin of gamma-rays.
Observations of the North Western region of W 44, also known as SRC-1 from previous works, were conducted with the MAGIC telescopes in the very-high-energy gamma-ray band. We analysed MAGIC data above 130 GeV exploiting the spatial information derived from the Fermi-LAT analysis above 1 GeV.

Here we show the results of both analyses and the combined Fermi-LAT and MAGIC spectra. An interpretation model was developed, assuming that the gamma-ray emission from the surroundings is due to clouds located near W 44 and illuminated by CRs escaping along the SNR’s magnetic field lines, thus obtaining constraining information on the diffusion coefficient of the escaped CRs.

Speaker: Riccardo Di Tria (Università degli Studi di Bari & INFN Bari)

ID448-RiccardoDiTria-W44_Fermi_MAGIC.pdf

16:00 Multiwavelength studies of Galactic PeVatron candidates with VERITAS

The spectral change of the cosmic ray flux at 10^15 eV (PeV) has been suggested as an indication of the maximum energy obtainable by Galactic accelerators. Since leptonic particles lose their energies rapidly as their energies increase, the detection of hard-indexed gamma-ray emission beyond ~100 TeV may indicate that those sources accelerate hadronic particles up to the PeV energy range. Recent results from ground-based air shower gamma-ray observatories, such as HAWC and LHAASO, have revealed a few of these PeVatron candidates. Combined information from multi-wavelength observations is essential to probe the nature of these PeVatron candidates. Observations with imaging atmospheric Cherenkov telescopes (IACTs) provide further information about the spatial and spectral energy distributions of the gamma-ray emission from these sources since IACTs have better angular resolution and better sensitivity from ~100 GeV up to ~10 TeV compared to the air shower gamma-ray observatories. Meanwhile, observations of non-thermal X-ray emission provide properties of the leptonic particles around the source regions, allowing modelling of the expected leptonic contributions at TeV energies. Here, we present the status of VERITAS observations of the PeVatron candidates including follow-up observations of LHAASO sources, and multi-wavelength studies of the Boomerang pulsar wind nebula.

Speaker: Nahee Park (Queen's University)

ID421_NPark_VERITAS_PeVatronStudy.pdf

16:15 On the origin of the complex energy-dependent structure of HESS J1702-420

HESS J1702-420 is an unidentified multi-TeV gamma-ray source with a peculiar energy-dependent morphology which most naturally can be explained as a composition of two independent emission components with significantly different spatial and energy distributions. Here we propose an alternative interpretation assuming that we deal with a single hadronic accelerator injecting protons with energies extending to at least 0.5 PeV. In the suggested scenario, both the extended (elongated) component of radiation with a soft gamma-ray spectrum and the compact point-like component with a very hard spectrum have the same origin associated with the interactions of injected protons with the surrounding dense gas environment but are produced at different stages of proton propagation. The component produced at the initial (quasi) ballistic regime of proton propagation has a compact image (angular distribution) focused on the accelerator and an energy spectrum which reflects the acceleration spectrum. The second (extended) component is the result of radiation at the stage when the protons enter the diffusion stage of propagation. Thus the image of this component reflects the spatial distribution of protons. Its spectrum is steeper because of the modulation of the proton spectrum in the course of diffusion. The joint analysis of these two components allows us to
derive the power-law index of the acceleration spectrum and the proton injection rate, and the energy-dependent diffusion coefficient. Assuming the distance to the source d=3.5 kpc, the characteristic medium density of 100 cm$^{-3}$ and diffusion coefficient $D(E)=3 \times 10^{27}$ cm$^2$/s we argue that the system can be well described by the protons' injection rate $\sim 7 \times 10^{38}$~erg/s. The latter
can be significantly reduced in the case of the association of HESS J1702-420 with significantly closer and denser molecular clouds seen along the line of sight in HI/CO surveys.

Speaker: Denys Malyshev (Tubingen University)

HESS_J1702_420___GAMMA2022.pdf

16:30 → 17:00 coffe break

17:00 → 18:30 Contributed Talks: EGAL parallel 4 (Aula Magna Ciències de la Terra) Chair: Núria Torres-Albà

17:00 Periodic Variability in gamma-ray Emitting Blazars with Fermi-LAT

Blazars display variable emission across the entire electromagnetic spectrum, which ranges in timescales from minutes to years. This variability is generally interpreted as stochastic and unpredictable processes. However, recent studies have inferred the presence of periodic signals coming from blazars. These could be caused by, e.g. a helical jet or a precessing jet due to the presence of a supermassive black hole binary. In this talk, we will report on the largest systematic search of periodic emission in the gamma-ray lightcurves of 350 blazars. Using 12 years of Fermi-LAT data, we have built a sample of 24 blazars displaying evidence of periodic emission. These results will be interpreted in the modeling framework of supermassive black holes binaries.

Speaker: Pablo Peñil (Clemson University)

gamma_conference_7_4_2022.pdf

17:15 Locating the blazar gamma-ray emitting zone from astrometric VLBI and Gaia data?

Although current emission models are generally able to account for the observed spectra of blazars from radio to TeV energies, unknowns remain on several fundamental questions such as the nature of the emitting particles, leptons or hadrons, the mechanism dominating the particle acceleration, and the origin of ultrafast variabilities. Some of the degeneracy between models could be removed by better localization of the gamma emission zone, which can be constrained but is not directly fixed by the low angular resolution gamma-ray data. Different locations can be considered such as the black hole magnetosphere, the radio core, the jet and knots detected in VLBI, or even more distant structures along the jets. Confronting the gamma-ray data with the very high precision absolute astrometry in the radio and optical ranges from the permanent geodetic VLBI program and the ESA Gaia mission should shed new light on this question.
We analyze a sample of about 816 active galactic nuclei (AGN) dominated by blazars, including a population of 214 BL Lacs and 488 FSRQs, cross-identified from the Gaia EDR3, the radio ICRF3, and the Fermi-LAT 4FGL catalogs. For a sub-sample of sources for which VLBI radio maps are available from the MOJAVE program, and within astrometric errors of less than 0.1 mas, most optical emissions (typically 90 %) detected by Gaia appear to be associated either with the VLBI radio core, or with a radio knot downstream in the jet at the parsec scale. We investigate the general trends of the main sample in terms of AGN classification, Gaia color indices, and GeV emission, and will discuss in particular the observed decrease of gamma-ray fluxes with the distance of the optical emission zone from the radio core, as well as the difference in behavior identified between the two populations of BL Lacs and FSRQs.

Speaker: Helene Sol (CNRS, LUTH, Observatoire de Paris)

ID370-HeleneSol-Blazar_gamma_ray_zone.pdf

17:30 Confronting observations of VHE gamma-ray blazar flares with reconnection models

Several models have been suggested to explain the fast gamma-ray variability observed in blazars, but its origin is still debated. One scenario is magnetic reconnection, a process that can efficiently convert magnetic energy to energy of relativistic particles accelerated in the reconnection layer. In our study, we compare results from state-of-the-art particle-in-cell simulations with observations of blazars at Very High Energy (VHE, E > 100 GeV). Our goal is to test our model predictions on fast gamma-ray variability with data and to constrain the parameter space of the model, such as the magnetic field strength of the unreconnected plasma and the reconnection layer orientation in the blazar jet. For this first comparison, we used the remarkably well-sampled VHE gamma-ray light curve of Mrk 421 observed with the MAGIC and VERITAS telescopes in 2013. The simulated VHE light curves were generated using the observable parameters of Mrk 421, such as the jet power, bulk Lorentz factor, and the jet viewing angle, and sampled as real data. This is the first time a comprehensive scan of the jet parameters has been evaluated in contrast with the observed data in a quantitative manner. With these results, we pave the way for future model-to-data comparison with next-generation Cherenkov telescopes, which will help further constrain the different variability models.

Speaker: Jenni Jormanainen (Finnish Centre for Astonomy with ESO)

ID431-JenniJormanainen-VHE_flares_reconnection.pdf

17:45 A shock-in-jet synchrotron mirror model

Previous work on time-dependent shock-acceleration and radiation
transfer in relativistic jets has successfully reproduced many
spectral variability features of blazars if flaring activity is
mediated by increasingly efficient diffusive shock acceleration.
However, flaring events exhibiting a significant increase of the
Compton dominance, or even "orphan" gamma-ray flares, are very
difficult to reproduce in this manner, suggesting that an enhancement
of an external radiation field for Compton scattering may be responsible
for the gamma-ray flaring. This work therefore investigates the signatures
of a synchrotron mirror model in which the synchrotron emission of
electrons accelerated by a mildly relativistic shock traveling along
the jet, is reflected by a cloud, and the reflected synchrotron
radiation acts as target photon field for enhanced Compton scattering
further down the jet. The model is applied to recent flaring events
exhibiting a significant enhancement of the Compton dominance in
3C279, and the expected spectral variability features are investigated
in detail.

Speaker: Markus Boettcher (North-West University)

#1293_Boettcher_synchrotron_mirror_pdf.pdf

#1293_Boettcher_synchrotron_mirror.pptx

18:00 Ultrahigh-energy cosmic-ray induced gamma-ray and neutrino fluxes from blazars

Blazars are potential candidates of cosmic-ray acceleration up to ultrahigh energies ( > 1 EeV). For an efficient cosmic-ray injection from blazars, 𝑝𝛾 collisions with the extragalactic background light and cosmic microwave background can produce gamma-ray and neutrino fluxes in the TeV and PeV-EeV energies, respectively. Such a line-of-sight cosmogenic gamma-ray flux can contribute to the spectra measured by ground-based air-Cherenkov telescopes from individual blazars, while PeV-EeV neutrinos form a “guaranteed” component in addition to any sub-PeV neutrinos produced in the blazar jet and as detected by IceCube. We calculate line-of-sight cosmogenic fluxes from the blazars TXS 0506+056, PKS 1502+106 and GB6 J1040+0617, which have been associated with IceCube neutrino events. We discuss conditions required for detection of these fluxes by current and upcoming gamma-ray and neutrino telescopes.

Speaker: Soebur Razzaque (University of Johannesburg Centre for Astro-Particle Physics)

Razzaque_GAMMA2022v2.pdf

18:15 Radio-gamma-ray response in blazars as a signature of adiabatic blob expansion

Multi-wavelength light curves in long-term campaigns show that, for
several blazars, the radio emission occurs with a significant delay with respect
to the  $\gamma$-ray band, with timescales ranging from weeks to years. Such
observational evidence has long been a matter of debate and is usually
interpreted as a signature of the $\gamma$-ray emission originating upstream in the
jet, with the emitting region becoming radio transparent at larger scales.
We show, by means of self-consistent numerical modelling, that
the adiabatic expansion of a relativistic blob can explain these delays,
reproducing lags compatible with the observed timescales. We use the
JetSeT framework to reproduce the numerical modelling of the radiative and
accelerative processes, reproducing the temporal evolution of a single blob,
from the initial flaring activity and the subsequent expansion, following the
spectral evolution and the corresponding light curves, investigating the
relations among the observed parameters, rise time, delay, and decay time, and
we identify the link with physical parameters. We find that, when
adiabatic expansion is active, lags due to the shift of the synchrotron
frequency occur. The corresponding time lags have an offset equal to the
distance in time between the flaring onset and the beginning of the expansion,
whilst the rising and decaying timescales depend on the velocity of the
expansion and on the time required for the source to exhibit a synchrotron
self-absorption frequency below the relevant radio spectral window. We derive an
inter-band response function, embedding the parameters mentioned above, and we
investigate the effects of the competition between radiative and adiabatic
cooling timescales on the response. We apply the response function to long-term
radio and γ−ray light curves of Mrk 421, Mrk 501, and 3C 273, finding satisfactory
agreement on the long-term behaviour, and we use a Monte Carlo Markov Chain approach to
estimate some relevant physical parameters. We discuss applications of the presented analysis
to polarisation measurements and to jet collimation profile kinematics. The collimation
profiles observed in radio images agree with the prediction from our model.

Speaker: Andrea Tramacere (Astronomy Department University of Geneva)

ID301-Tramacere-Andrea-radio_gamma_delay_adb_exp.pdf

17:00 → 18:30 Contributed Talks: GAL parallel 4 (Aula Magna Biologia) Chair: Brian Reville

17:00 Multiwavelength investigation of LHAASO J1908+0621: an unidentified galactic PeVatron

Recently LHAASO has detected more than a dozen of ultra-high energy (UHE) $\gamma$-ray sources in our Galaxy. Many of these seem to be connected with PWNe or SNRs (see Cao et al., 2021).
Among these sources, one of the best PeVatron candidates is LHAASO J1908+0621, a remarkable source for its hard spectrum extending beyond 100 TeV and with no evidence of a cutoff. This source was also detected by other $\gamma$-ray instruments as HAWC, VERITAS and HESS.
Due to the complexity of the morphological structure of the source and the limited angular resolution, the origin of its $\gamma$-ray emission has not yet been unambiguously identified. There are several objects in the region which could serve as counterparts to the TeV emission, including a supernova remnant (SNR G40.5-0.5) and various pulsars, precluding a firm identification of the extreme accelerator and making it difficult to distinguish between a hadronic or leptonic nature of the emission. Additionally, the LHAASO source is associated with an ICECUBE neutrino hotspot, although the significance is still too low (see Aartsen et al., 2020).

We performed a multi-wavelength analysis of LHAASO J1908+0621 to investigate its nature and the origin of its ultra high-energy emission (see Crestan
et al., 2021). Using the Nobeyama Radio Observatory data on $^{12}$CO and $^{13}$CO molecular line emission, we found evidence of dense molecular clouds spatially correlated with the source region. Moreover, the 12-year analysis of Fermi-LAT data stresses the presence of a counterpart with a hard spectrum between 10 GeV and 1 TeV. Our new analysis of the XMM-Newton data translates into better constraints on the X-ray flux from this source. Thanks to the multi-wavelength approach, we showed that a single zone model cannot explain the whole set of multi-wavelength data, regardless of whether it accelerates protons or electrons, but a 2-component model is needed to explain the emission from LHAASO J1908+0621. The UHE emission appears most likely the superposition of a TeV PWN powered by PSR J1907+0602, in the southern part, and of the interaction between the supernova remnant G40.5-0.5 and the molecular clouds towards the northern region.

Speakers: silvia crestan (INAF-IASF Milano), Dr Andrea Giuliani (INAF - IASF Milano), Dr Sandro Mereghetti (INAF - IASF Milano), Dr Lara Sidoli (INAF - IASF Milano), Dr Fabio Pintore (IASF - INAF Milano), Dr Nicola La Palombara (INAF - IASF Milano)

ID507_CrestanSilvia_LHAASO J1908+0621.key

17:15 Origin of pulsar radio emission

For more than five decades, the origin of pulsar coherent radio emission has been one of the major unsolved problems in astrophysics. In this talk, I describe the results of our first-principles simulations of electron-positron pairs creation near magnetic poles of neutron stars - the process responsible for filling pulsar magnetosphere with dense pair plasma - which provide a clue to this long-standing mystery. We directly demonstrate that the intermittency of the pair creation process and its naturally-arising non-uniformity across magnetic field lines lead to the emission of strong coherent electromagnetic waves with properties commensurate with that of the observed pulsar radio emission. These waves are only moderately damped by dense plasma and should escape the magnetosphere and be observable as coherent radio emission. Our findings will lay the theoretical foundation for the interpretation of a plethora of observational phenomena seen in radio pulsars, magnetars, and possibly FRBs.

Speaker: Andrey Timokhin (University of Zielona Gora)

timokhin_Barcelona_2022.pdf

17:30 On the potential of bright, young pulsars to power ultra-high gamma-ray sources

The recent discovery of a new population of ultra-high-energy gamma-ray sources with spectra extending beyond $100 \, \rm TeV$ revealed the presence of Galactic PeVatrons - cosmic-ray factories accelerating particles to PeV energies. These sources, except for the one associated with the Crab Nebula, are not yet identified. With an extension of 1 degree or more, most of them contain several potential counterparts, including Supernova Remnants, young stellar clusters and Pulsar Wind Nebulae (PWNe), which can perform as PeVatrons and thus power the surrounding diffuse ultra-high energy gamma-ray structures. In the case of PWNe, gamma rays are produced by electrons, accelerated at the pulsar wind termination shock, through the inverse Compton scattering of 2.7 K CMB radiation. The high conversion efficiency of pulsar rotational power to relativistic electrons, combined with the short cooling timescales, allow gamma-ray luminosities up to the level of $L_\gamma \sim 0.1 \dot{E}$. The pulsar spin-down luminosity, $\dot E$, also determines the absolute maximum energy of individual photons: $E_{\rm \gamma~\rm max}\approx 0.9 \dot E_{36}^{0.65}~~\rm{PeV}$. This fundamental constraint dominates over the condition set by synchrotron energy losses of electrons for young PWNe with typical magnetic field of $\approx$100~$\mu$G with $\dot{E} < 10^{37}\ \rm erg/s$. We will discuss the implications of $E_{\rm \gamma~\rm max}$ by comparing it with the highest energy photons reported by LHAASO from a dozen of ultra-high-energy sources.

Speaker: Emma de Ona Wilhelmi (DESY)

Gamma2020_v5.pdf

17:45 Probing the population of pulsar halos with Fermi-LAT

Over the past years, the detection of extended gamma-ray emission surrounding young and middle-aged pulsars has been reported in the GeV and TeV domains. This emission is interpreted as inverse-Compton scattering of ambient photons by halos of energetic electron/positron pairs accelerated in pulsars and their wind nebulae and confined in their vicinity by a mechanism yet to be elucidated. These pulsar halos offer an opportunity to probe the transport properties of energetic particles in the vicinity of their accelerators. As an emerging population of gamma-ray sources, halos can be expected to have a non-negligible contribution to the GeV–TeV emission from the Galaxy in the form of yet unidentified sources and/or spatially unresolved gamma-ray emission. We have performed a systematic search for extended > 10 GeV emission components along the Galactic plane using 13 years of Fermi-LAT data. We have found about 60 such components with angular sizes up to a few degrees, a fraction of which may be pulsar halos. We assess the likelihood of the latter possibility by comparing the properties of the whole sample of extended components to the predictions of a population synthesis model. We then present a short list of promising halo candidates possibly associated with TeV sources, together with dedicated analyses in which we investigate more in depth the morphology and spectrum of these selected targets.

Speaker: Soheila Abdollahi (IRAP/CNRS)

ID387_SoheilaAbdollahi_Probing_GeV_Halos_Population

18:00 Are pulsar halos rare ?

Extended gamma-ray emission, interpreted as halos formed by the inverse-Compton scattering of ambient photons by electron-positron pairs, is observed towards a number of middle-aged pulsars. The properties of the emission suggest the possibility of a very efficient confinement of the particles over tens of parsec. The physical origin and actual commonness of the phenomenon in the Galaxy remain unclear. The level of diffusion suppression seems extreme compared to what can be achieved in most recent theoretical models.

Using a phenomenological two-zone diffusion framework in the light of Fermi-LAT, HAWC, and AMS-02 data, we searched for model setups minimizing as much as possible the extent and magnitude of diffusion suppression in the halos around J0633+1746 and B0656+14. Extrapolating these descriptions to all other nearby middle-aged pulsars, we show that the resulting combined positron flux including the contribution from Geminga would saturate the AMS-02 measurement above 100GeV for injection efficiencies that are much smaller than those inferred for the canonical halos in J0633+1746 and B0656+14, and more generally with the values typical of younger pulsar wind nebulae. This suggests the possibility that most middle-aged pulsars do not develop halos, with an occurrence rate of the phenomenon possibly being as low as ∼5−10%, although the evidence supporting that depends on the actual properties of the local pulsar population and on the uncertain physics driving the formation and evolution of halos.

We searched for complementary evidence for the rarity or commonness of pulsar halos by performing a population synthesis for the Milky Way, with a simple but coherent approach for the PWN-halo evolutionary sequence. Pulsar halos are shown to be viable counterparts to a fraction of the currently unidentified sources if they develop around most middle-aged pulsars, and the number of detectable halos in existing or future surveys ranges from 30 to 80% of the number of detectable PWNe. The level of diffuse emission from unresolved populations in each survey is found to be dominated by halos and comparable to large-scale interstellar radiation powered by cosmic-rays above 0.1–1 TeV. Yet, if pulsar halos are rare, as suggested from the local positron flux constraint, the total number of currently known TeV sources including unidentified ones cannot be accounted for in our model from young PWNe only. This calls for continued efforts to model pulsar-powered emission along the full evolutionary path, including the late stages past the young nebula phase.

Speaker: Pierrick Martin (CNRS/IRAP)

ID379-PierrickMartin-rare_pulsar_halos.pdf

18:15 New TeV halo candidate surrounding PSR J0359+5414 detected with the HAWC Observatory

The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the gamma-ray sky between a hundreds of GeV and hundreds of TeV, and has detected emission surrounding a radio-quiet pulsar, PSR J0359+5414, in its almost 6 years of data. PSR J0359+5414 is gamma-ray pulsar with an age of 75 kyr and an extremely high spin-down power > $10^{36}$ erg/s. Its pulsar wind nebulae is detected in X-ray with a size of 30 arcseconds. We present results of the HAWC analysis of PSR J0359+5414. We show that the very-high-energy (VHE) emission around PSR J0359+5414 has a similar spectrum and extension as the TeV halo around the Geminga pulsar. Our observation of this relatively young middle-aged pulsar further confirms that particles diffuse slowly in the vicinity of pulsars.

Speaker: Sara Coutiño de León (University of Wisconsin-Madison)

ID419_SaraCoutino_TeVhalo.pdf

19:15 → 21:00 Sports Event

Wednesday 6 July

09:30 → 11:00 Review Talks: Wednesday (Aula Magna Biologia) Chair: Josep Martí

09:30 Galactic Cosmic Rays

Significant advances have been made in cosmic-ray measurements in recent years, particularly with successful space missions and long-duration balloon flights over Antarctica. The high precision data from these missions over a wide energy range led to surprising discoveries, such as an excess of positrons at high energies and hardening of the elemental spectra. These unexpected spectral features present significant challenges for Galactic cosmic-ray models on their origin, propagation, and acceleration. Recent results and their implications will be presented, and the outlook will be discussed.

Speaker: Eun-Suk Seo (University of Maryland)

ID506_EunSukSeo_GCR.pdf

10:15 Multi-wavelength view of pulsars: from millisecond pulsars to magnetars

In this review talk I will present the state-of-the-art of pulsar observations in different observing bands, from radio to very high energy gamma-rays, with a particular focus on the different emission mechanisms in place. Furthermore, I will focus on the low-B millisecond pulsars and the high-B magnetars, comparing their multi-band spectra and showing new interesting results of the past few years.

Speaker: Nanda Rea

Rea_Barcelona_TeVMeeting_july2022_v5_pdf_version.pdf

11:00 → 11:30 coffee break

11:30 → 12:20 Highlight Talks topical: Wednesday (Aula Magna Biologia) Chair: Roberta Zanin

11:30 Gamma-ray emitting binaries

Binary systems are today well established gamma-ray emitters, and the variety of the processes responsible for this emission is a hard act to follow among any other high-energy source class. After years of faithful perspectives, extensive theoretical modelling and complex MHD simulations, GeV/TeV detectors have reported a too rich phenomenology to be predicted just a few years ago. I will review in this talk some of the most challenging highlights in binary systems in the gamma-ray domain, from orbitally modulation to orphan flares in pulsar gamma-ray binaries to gamma-rays in microquasar jet/medium interactions regions and powerful explosions in novae systems.

Speaker: Pol Bordas (ICCUB)

ID249-PBordas_Gamma_ray_emitting_binaries.pdf

11:55 Nova explosions

Classical and recurrent nova explosions occur on top of white dwarfs accreting H-rich matter from a companion main sequence or red giant star, in a close binary system. In the recent years, since the launch of the Fermi Gamma-Ray satellite by NASA in 2008, several novae have been detected by Fermi/LAT (LAT: Large Area Telescope) in High-Energy Gamma Rays, with energies larger than 100 MeV. This emission is known to be related to the acceleration of particles in the internal and/or external shocks occurring early after the thermonuclear nova explosion. However, Very High Energy Gamma-Rays produced as a consequence of nova explosions have only being discovered very recently, in the recurrent nova RS Oph, that had an outburst in August 2021. These require the acceleration of protons, and not only of electrons; this was in fact predicted theoretically - based in observations at other wavelengths - in the previous eruption of RS Oph, in 2006, but has not been confirmed observationally until now.

I will review the origin of the different types of gamma-ray emission in novae and highlight the relevance of the recent VHE gamma-rays discoveries for the nova theory, mainly in the field of the mass ejection and the associated particle (electrons and protons) acceleration processes.

Speaker: Margarita Hernanz (Instituto de Ciencias del Espacio (CSIC) & IEEC)

ID494-MargaritaHernanz_NovaExplosions.pdf

12:20 → 12:45 Highlight Talks observational: Wednesday (Aula Magna Biologia) Chair: Roberta Zanin

12:20 LHAASO Highlights in gamma-ray Astronomy

The Large High Altitude Air Shower Observatory (LHAASO) as the largest ground based Gamma Ray detector array is built up. The full array has been operated for months. Many VHE gamma ray sources has been observed including well known sources such as the Crab and Mkr421. With many sources found having strong emission of gamma rays in UHE(> 0.1 PeV) band, LHAASO starts the era of the UHE gamma ray astronomy. With its unprecedented sensitivity at energies above 10 TeV and extremely high background rejection capability, super-PeV gamma-like events, including the record high energy of 1.4 PeV, are detected first time in history. With also measured SEDs of several galactic gamma sources above 0.1 PeV, LHAASO reveals that our galaxy is full of PeVatrons. The extreme features of the electron PeVatron inside the Crab pose strong challenges to models and even more fundamental theories. Those discoveries enable an exploring for hadronic PeVatrons, i.e. origins of cosmic rays. The highest energy photons provide opportunities of checking for validity of fundamental rules, such as the Lorentz Invariance.

Speaker: Zhen Cao (Institute of High Energy Physics)

12:45 → 13:15 POSTER time

13:15 → 15:00 lunch break

15:00 → 16:30 Contributed Talks: EGAL parallel 5 (Aula Magna Ciències de la Terra) Chair: Jonathan Biteau

15:00 Probing the intergalactic magnetic field through gamma-ray observations with the Fermi LAT and H.E.S.S.

Magnetic fields in galaxies and galaxy clusters are believed to be the result of the amplification of seed fields during structure formation. However, the origin of this intergalactic magnetic field (IGMF) remains unknown. Observations of high-energy gamma rays from distant blazars offer an indirect probe of the IGMF. Gamma-rays interact with the extragalactic background light to produce electron-positron pairs, which can subsequently initiate electromagnetic cascades whose gamma-ray signature depends on the IGMF. Here, we report on a new search for the cascade emission using a combined data set from the Fermi Large Area Telescope (LAT) and the High Energy Stereoscopic System (H.E.S.S.). Using state-of-the-art Monte Carlo predictions for the cascade signal, our preliminary results exclude an IGMF $< 7\times10^{-16}$G for a coherence length of 1 Mpc even when blazar duty cycles as short as 10 years are assumed. This improves previous limits by a factor of 2.

Speaker: Manuel Meyer (University of Hamburg)

ID260-ManuelMeyer-IGMF_HESS_Fermi.key

ID260-ManuelMeyer-IGMF_HESS_Fermi.pdf

15:15 Hunting the gamma-ray emission from Fast Radio Burst with Fermi-LAT

Fast radio bursts (FRBs) are one of the most exciting new mysteries of astrophysics. Their origin is still unknown, but recent observations seem to link them to soft gamma repeaters and, in particular, to magnetar giant flares (MGFs). The recent detection of a MGF at GeV energies by the Fermi Large Area Telescope (LAT) motivated the search for GeV counterparts to the >1000 currently known FRBs. To date, none of these has a known gamma-ray counterpart.
Taking advantage of more than 12 years of Fermi-LAT data, we perform a search for gamma-ray emission from almost all the reported repeating and non-repeating FRBs. We analyze on different time scales the Fermi-LAT data for each individual source separately and perform a cumulative analysis on the repeating ones. In addition, we perform the first stacking analysis at GeV energies of this class of sources in order to constrain the gamma-ray properties of the FRBs. The stacking analysis is a powerful method that allows for a possible detection from below-threshold FRBs providing important information on these objects. In this talk we present the results of our study and we discuss their implications for the predictions of gamma-ray emission from this class of sources.

Speaker: Giacomo Principe (University of Trieste)

FRB_search_with_Fermi_LAT_Principe_Giacomo.pdf

15:30 Gamma-ray Blazars above 100 MeV: density, evolution and origin of the Extragalactic Gamma-ray Background

The mystery of the extragalactic gamma-ray background (EGB) has been investigated since its first detection. To unveil its origin and composition, it is necessary to resolve the different gamma-ray emitting populations. Relying on 8 years of Fermi-Large Area Telescope data, we obtained the most sensitive source count distribution of blazars >100 MeV to date. This allowed us to derive the contribution of blazars to the EGB, highlighting that this population cannot reproduce the entire EGB and that, indeed, another source class is required to explain the residual emission. For the first time, we were also able to differentiate between possible evolutionary paths of this elusive source class, and derive that a density evolution is preferred. In this talk, I will present the latest results of our analysis in light of blazars' evolutionary models and discuss future prospects for the luminosity function study of gamma-ray blazars.

Speaker: Lea Marcotulli (Yale University)

ID1250_Gamma_Blazar_evolution_Marcotulli_L.pdf

ID1250-MarcotulliLea_Gamma_Blazar_evolution

15:45 The gamma-ray morphology of M87 and the cosmic-ray pressure in the Virgo Cluster with H.E.S.S.

The Active Galactic Nucleus feedback is a potential heating mechanism, which solves the Cooling Flow (CF) Problem in Cool Core (CC) clusters. The cosmic-ray from the jet interact with the Intra-Cluster Medium (ICM) producing neutral pions, which decay to gamma rays, originating a steady and spatially extended gamma-ray signal. However, no gamma-ray observations could yet be associated with cluster diffuse emission. 

The High Energy Stereoscopic System (H.E.S.S.) is an array of five Imaging Atmospheric Cherenkov Telescopes (IACTs) located in Namibia. The H.E.S.S. telescopes are sensitive to Very-High-Energy (VHE) gamma rays between ~30 GeV and ~100 TeV and have being observing M87 since 2004. M87 is one of the closest radio-galaxies, at $\sim$16.5$\,$Mpc from Earth, at the center of the CC Virgo Cluster.

In this work, we analyze H.E.S.S. observations of M87 and classify the source emission into low, intermediate and high states. No significant gamma-ray extension was detected in the low state, leading to a 99.7% confidence level (c.l.) upper limit on the σ extension of 0.016$^\circ$ $\approx$ 4.6$\,$kpc. The volume-averaged cosmic-ray pressure ratio <XCR> is constrained to $\leq$20% within the inner 20$\,$kpc at 99.7% c.l., considering two different approaches and a hard proton spectral index.

A cluster emission could not be detected, although it can not be ruled out. The Cherenkov Telescope Array Observatory (CTAO) will be the next generation of IACTs. With a better sensitivity and angular resolution, it has the potential to unravel M87 extended emission and help solve the CF problem.

Speaker: Victor Barbosa Martins (DESY, D-15738 Zeuthen, Germany)

#362_BarbosaMartins_M87morphology.pdf

16:00 Virial shocks in galaxy clusters

In the theory of structure formation in the Universe, galaxy clusters are thought to grow by accreting surrounding material, resulting in strong surrounding, so-called virial shocks. Such a shock is expected to accelerate relativistic electrons, thus generating a spectrally-flat leptonic virial ring. Recently, we have detected ($>5\sigma$) virial shock signals around the expected shock radius, ~(2--3)$\theta_{500}$, for example by stacking gamma-ray data from Fermi LAT around >100 nearby clusters. We investigate virial shock signals in a wide range of wavelengths, to better understand these shocks and their implications for astrophysics, cosmology, and plasma physics. In particular, we estimate the energies the shock deposits in relativistic particles and magnetic fields.

Speaker: Kuan-Chou Hou (Ben-Gurion University of the Negev)

ID430-KuanChouHou-Virial_shocks_in_galaxy_clusters.pdf

16:15 VERITAS Search for Gamma-ray and Optical Counterparts to Fast Radio Bursts

Detecting and understanding transients have proven one of the most fruitful areas of study in the field of multi-messenger and gamma-ray astrophysics. Imaging Atmospheric Cherenkov Telescopes explore an interesting parameter space with a high sensitivity to rapid events when compared to other instruments. One of the most rapid transients currently under study is Fast Radio Bursts (FRBs). FRBs are an expanding source class of rapid (~ms) bursts of radio emission. Many questions remain about the properties of their potential multi-wavelength counterparts. Dedicated radio instruments have enabled an order of magnitude increase in the number of bursts detected, but simultaneous multi-wavelength observations remain challenging. This is primarily due to the observational difficulties caused by their short-lived and sporadic nature. IACTs can simultaneously probe two interesting wavelength bands, optical and Very High Energy (VHE; >~100 GeV) gamma rays, making them an ideal instrument to follow-up known repeating FRBs. Following up FRBs and understanding the challenges relating to these observations is not only important for our understanding of the progenitors of FRBs but also for the future of IACT follow-up of other optical/gamma-ray targets like microquasars, pulsars, and M-dwarfs. In this talk, I will summarize the extensive FRB follow-up program at VERITAS including discussions of the simultaneous rapid optical and VHE observations of three bursts from FRB20180916B in 2021. Ongoing work with the study of 6 other repeaters and the status of the optical program at VERITAS will also be presented.

Speaker: Matthew Lundy (McGill University)

ID438_MatthewLundy_FRB.pdf

15:00 → 16:30 Contributed Talks: GAL parallel 5 (Aula Magna Biologia) Chair: Margarita Hernanz

15:00 Gamma-ray emission of hadronic origin from nova RS Oph revealed by the MAGIC telescopes

The recurrent symbiotic nova RS Ophiuchi (RS Oph), which exhibits eruptive events once every 15 years, displayed its latest major outburst on August 2021. This eruption was detected from radio up to very-high-energy (VHE) gamma rays, making of RS Oph the first nova discovered in the VHE regime. After receiving the optical and high-energy triggers, the MAGIC telescopes performed a followed-up campaign on this source and detected the nova from August 09 to 12. The emission observed by MAGIC prove a hadronic origin of the gamma-ray component. In this talk, we will report on the results obtained by MAGIC during the RS Oph 2021 eruption, coupled with some modeling interpretations.

Speaker: Alicia López-Oramas (Instituto de Astrofísica de Canarias (IAC))

ID222_Alicia_Lopez-Oramas_RSOph_Gamma2022.pdf

15:15 Efficient cosmic-ray acceleration in the recurrent nova RS Ophuichi revealed by H.E.S.S.

Recurrent Novae (RNe) undergo episodic eruptions in the form of thermonuclear explosions, due to the accumulation of material accreted by a white dwarf from a binary companion star.
The well known RN RS Ophiuchi (RS Oph) underwent its latest eruption in August 2021, triggering numerous follow-up observations, including with the High Energy Stereoscopic System (H.E.S.S.).
H.E.S.S. is an array consisting of five Imaging Atmospheric Cherenkov Telescopes (IACTs) situated in Khomas Highland, Namibia, that observes the sky in the very-high-energy (VHE) gamma-ray regime of 100 GeV to a few tens of TeV.
Non-thermal emission was observed coincident with the nova eruption within the first days and up to a month after the initial burst event, establishing novae as Galactic transients reaching TeV energies. Analysis and interpretation of the data identify time-resolved acceleration of cosmic-rays, constraining models of particle energisation. Combining the data taken by H.E.S.S. with concurrent observations taken by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, a consistent temporal and spectral profile is observed, favouring a common origin to the emission. The detection and interpretation of the non-thermal VHE emission from the RN RS Oph by H.E.S.S. will be presented.

Speaker: Simon Steinmassl (Max Planck Institut fuer Kernphysik)

ID309-SimonSteinmassl-RSOph_hess.pdf

15:30 RS Ophiuchi nova outburst detection by the LST-1

In August 2021, the recurrent symbiotic nova RS Ophiuchi experienced an outburst detected in the optical and high-energy gamma rays. This detection triggered follow-up observations of the source at very-high-energy (VHE) gamma rays with the Large-Sized Telescope prototype (LST-1) of the upcoming Cherenkov Telescope Array (CTA) Observatory. RS Ophiuchi was observed for several nights after the outburst and it was detected by the LST-1. In this contribution, we report the results of this observation campaign on the first nova ever detected at VHEs and discuss the obtained results in a multiwavelength context.

Speaker: Arnau Aguasca-Cabot

ID294_AguascaCabot_LST1RSOph.pdf

15:45 Revealing the particle acceleration in stellar wind shocks of massive colliding wind binaries

Binary systems comprising massive stars in relatively close orbits allow the presence of strong interaction between the two winds of the components. When the distance is close enough, an energetic shock is produced due to the collision of the two stellar winds, which can shine from radio wavelengths to very high energy gamma-rays.
These regions have proven to be extremely efficient environments to accelerate particles up to relativistic energies, involving higher mass, photon, and magnetic energy densities than their analogue processes in supernova remnants or interstellar bow-shocks. However, only a few of these systems are know to exhibit an exceptionally powerful and extreme region that could lead to emission in the high energy, and even in the very high energy range. Until recently, only Eta Carinae was the only colliding wind binary with such potential emission.

Thanks to very-high-resolution radio observations it is possible to trace in detail the wind collision region, characterizing the energy budget, magnetic field, and stellar wind properties of the two stars. Given that it is the same particle population producing the radio and the high-energy non-thermal emission, these studies allow tighter predictions on the high energy range.
In this talk I will discuss the discovery of two colliding wind binaries, HD 93129A and Apep, that have been predicted to produce emission at gamma rays, detectable by either Fermi or even CTA in the future. These sources would double the current detection of high-energy colliding wind binaries known up to now.

These studies require efforts covering the full electromagnetic spectrum, and combining both observational and theoretical point of views. To improve the relations between the different groups we have recently established the PANTERA-Stars (Particle Acceleration and Non-Thermal Emission of Radiation in Astrophysics - Stars) collaboration.

Speaker: Benito Marcote (Joint Institute for VLBI ERIC (JIVE))

ID407-BenitoMarcote-shocks-in-colliding-wind-binaries.pdf

16:00 Non-thermal emission from colliding-wind binaries

Here we present an overview of the physics behind the non-thermal emission from massive colliding-wind binaries (CWBs). In these systems the hypersonic and powerful stellar winds collide and give rise to strong shocks capable of accelerating relativistic particles. We introduce a model for CWBs that takes into account how relativistic particles travel along the shocked region while cooling and radiating by different mechanisms, as well as the absorption processes that affect their broadband emission. We present results from applying this model to the CWBs HD 93129A and Apep. In particular, we investigate the relativistic particle content and magnetic field intensity in the wind-collision region. We highlight the great synergy between observations at low radio frequencies and high-energy X-rays and $\gamma$-rays for studying the non-thermal processes in CWBs.

Speaker: Santiago del Palacio (Chalmers University of Technology)

ID311-Santiago-del-Palacio_Colliding_wind_binaries.pdf

16:15 The 2020 periastron of Eta Carinae at high-energies

Colliding-wind binaries are massive stellar systems featuring strong, interacting stellar winds. The resulting shocks may act as effective particle accelerators, making them good candidates for detection at high energies. However, only the massive binary Eta Carinae (with an orbital period of ~ 5.5 years) has been firmly identified as a gamma-ray source. A second system, Gamma² Velorum, was found positionally coincident with a gamma-ray signal, with solid evidence of orbital variability along its orbit. Thus massive binaries are a promising, emerging class of high-energy emitters.

However, the origin of the non-thermal emission in Eta Carinae is still unclear, with both leptonic and hadronic scenarios currently under discussion. Moreover, gamma-ray fluxes differ between the two periastrons previously observed by the Fermi Large Area Telescope (Fermi-LAT). Here we report the analysis of the 2020 periastron, together with a complete analysis of more than two orbits, allowing the first orbit-to-orbit variability study of Eta Carinae at GeV energies.

We discuss these results in the context of previous hard X-ray (NuSTAR) and very-high-energy (H.E.S.S.) observational results. This new analysis provides highly valuable information for the radiative scenarios and the conditions of the wind-collision region.

Speaker: Guillem Martí-Devesa (University of Innsbruck)

313_Marti-Devesa_EtaCar.pdf

16:30 → 17:00 coffee break

17:00 → 18:30 Contributed Talks: GAL parallel 6 (Aula Magna Biologia) Chair: Valentí Bosch-Ramon

17:00 Radio pulsations from LS I 61 303

LS I +61 303 303 is one of the rare gamma-ray binaries, emitting most of their luminosity in photons with energies beyond 100 MeV. The ~26.5 d orbital period is clearly detected at many wavelengths. Additional aspects of its multi-frequency behavior make it the most interesting example of the class. The morphology of high-resolution radio images changes with orbital phase displaying a cometary tail pointing away from the high-mass star. LS I +61 303 303 also shows superorbital variability. A couple of energetic (~ 10^37 erg/s), short, magnetar-like bursts have been plausibly ascribed to it. LS I +61 303 303's phenomenology has been put under theoretical scrutiny for decades, but the lack of certainty regarding the nature of the compact object in the binary has prevented advancing our understanding of the source. Here, using observations done with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report on the existence of transient radio pulsations from the direction of LS I +61 303 303. We find a period P=269.15508 (\pm) 0.00016 ms at a significance of > 20 sigma. This is the first evidence for pulsations from this source at any frequency, and strongly argues for the existence of a rotating neutron star in LS I +61 303 303. We try to put this measurement in the context of models of the source, analyzing the possible state such pulsar could be in, and what kind of magnetospheric gamma-ray emission could be expect from it, if any.

Partly based on the paper published in Nature Astronomy (March 2022)
(https://doi.org/10.1038/s41550-022-01630-1)
by Shan-Shan Weng, Lei Qian, Bo-Juan Wang, D. F. Torres, A. Papitto, P. Jiang,
Renxin Xu, Jian Li, Jing-Zhi Yan, Qing-Zhong Liu, Ming-Yu Ge, and Qi-Rong Yuan

Speaker: Diego F Torres (ICREA & Institute of Space Science (ICE, CSIC))

Torres_radio_pulsations_LSI-2022.pdf

17:15 VERITAS observations of gamma-ray binaries

VERITAS, an array of four 12-m imaging atmospheric Cherenkov telescopes, has been fully operational since April 2007. One of the key VERITAS science programs have included the search for and monitoring of gamma-ray binaries. The gamma-ray binary systems are composed of a massive star and a compact object, black hole or neutron star. Their spectral energy distributions peak above 1 GeV. VERITAS archive consists of more than 200 hr of datasets for HESS J0632+057 and LS I +61° 303, having orbital period of ~316.7 days and ~26.5 days, respectively. We will discuss the status and results from the VERITAS and Swift-XRT observations for these binary systems.

Speaker: Sonal Ramesh Patel (Deutsches Elektronen-Synchrotron DESY)

GammaRay_Binary_Gamma2022_Sonal.pdf

17:30 H.E.S.S. Observations of the 2021 PSR B1259-63 Periastron

PSR B1259-63 is a gamma ray binary system, hosting a confirmed pulsar in an eccentric, 3.4 year, orbit around an O9.5Ve star (LS 2883). We report results obtained in the TeV domain with H.E.S.S., from an extensive observation campaign of the 2021 periastron period. The data set comprises of over 100 hours of data spanning six months and therefore permits an unprecedented insight into the behaviour of the system at TeV energies. In the X-ray and GeV domains, the source exhibited distinct differences in its emission behaviour in 2021 than in previous periastron passages. Specifically, while the impact of the two disk crossings of the pulsar around periastron are observed in X-rays as usual, albeit with somewhat lower fluxes, a third peak has appeared at $t_p+30$~d; a point around which in the past a GeV flaring event regularly occurred. Conversely, the GeV flaring event in 2021 was significantly delayed. We present the results of an X-ray/TeV light curve correlation study as well as studies of the TeV spectral variability during the periods of the third X-ray peak and the GeV flare.

Speaker: Charles Thorpe-Morgan (IAAT- University of Tübingen)

ID403-CharlesThorpeMorgan-HESS_Observations_of_PSRB1259-63_2021_Periastron_title.pdf

17:45 Radio to GeV view of PSRB 1259-63 periastron passage in 2021.

PSR B1259-63 is a gamma-ray binary system hosting a radio pulsar orbiting around a massive young star, LS 2883, with a period of ∼3.4 years. The interaction of the pulsar wind with the LS 2883 outflow leads to unpulsed broadband emission in the radio, X-ray, GeV, and TeV domains. One of the most unusual features of the system is an outburst of GeV energies around the periastron, during which the energy release substantially exceeds the spin down luminosity under the assumption of the isotropic emission. In this talk, we will present the results of a recent multi-wavelength campaign (radio, optical, and X-ray bands) including the unpublished yet evolution of radio polarization and spectral slope. The campaign covered a period of more than 100 days around the 2021 periastron and revealed substantial differences from previously observed passages. In this talk we will compare the obtained data set with the predictions of the emission cone model proposed by us previously.

Speaker: Masha Chernyakova (DCU)

grlb_Barcelona_2022.pdf

18:00 Modelling Wind Dynamics and Gamma-Ray Emission from LS 5039

We present our numerical model for the gamma-ray binary LS 5039, where we utilise a pulsar-wind-driven scenario. In our model the high-energy particle transport is treated jointly with the simulation of the relativistic pulsar wind. Thus, dynamical effects of the turbulent interaction between stellar and pulsar wind can directly translate to the dynamics of the energetic particles. From the resulting distribution function of the energetic particles, we compute their gamma-ray emission as a function of orbital phase and presumed viewing-angle of the system. Our model reproduces observations of the main spectral features of the emission from the system. Where our results deviate from observations, we identify possibly shortcomings of the model. We end with an outlook on related model improvements, showing first-results of new high-resolution simulations of the LS-5039 system.

Speaker: Ralf Kissmann (Universität Innsbruck)

ID391_RalfKissmann_Modelling_LS5039.pdf

18:15 Investigating the puzzling radio structures of the gamma-ray binary LS 5039

LS 5039 is a gamma-ray binary system hosting a compact object and a massive O-type stellar companion. It presents a broadband emission spectrum that goes from radio up to gamma rays with energies of a few dozen TeV. There are two main physical scenarios proposed to explain this emission, both of them involving charged particle acceleration up to ultra-relativistic energies and their subsequent non-thermal radiative cooling as they propagate through a relativistic outflow. In the microquasar scenario, most of the non-thermal emission is originated in jets launched from the compact object. In the pulsar-wind scenario, in which the compact object is always a non-accreting pulsar, the non-thermal radiation comes from an outflow produced by the interaction of the pulsar and stellar winds.

In this contribution, we will present a semi-analytical model that computes the dynamical evolution of the outflows of LS 5039 in both scenarios. Using this hydrodynamical information, the model also includes a consistent computation of the radiation expected from this system. In particular, with the aim of discriminating between the two scenarios, we compute the extended radio emission of LS 5039 in both the microquasar and pulsar-wind cases, and compare it with the available observational data.

Speaker: Edgar Molina (Universitat de Barcelona - ICCUB)

2022_Gamma_GSlides

2022_Gamma.pdf

17:00 → 18:30 Contributed Talks: THEORY parallel (Aula Magna Ciències de la Terra) Chair: Benoit Cerutti

17:00 Relativistic magnetic bombs

We develop models of magnetically-driven relativistic explosions, with application to flares from Soft Gamma-Ray Repeaters and Fast Radio Bursts. Non-stationarity, and the conservation of magnetic flux make magnetized explosion qualitatively different from stationary MHD flows, as well as fluid explosions. We study generation of relativistic coronal ejection, conditions for generating causally-disconnected flows, and later dynamics of ejected structures.

Speaker: Maxim Lyutikov (Purdue University)

Lyutikov-Heidelberg2022.key

Lyutikov-Heidelberg2022.pdf

17:15 Particle acceleration via magnetic reconnection near spinning black holes coupled to a surrounding disk

Accretion and ejection have been found to be tightly linked around stellar-mass and supermassive black holes. The monitoring of Sagittarius A*, M87 and Cygnus X-1 suggest that this junction is mediated by an intense and structured magnetic field embedded in a collisionless plasma within a few 10 gravitational radii. These environments are also prone to recurring non-thermal flares whose origin remains unclear.

In this talk, I will focus on configurations where a Kerr black hole is surrounded by a disk and a hot corona threaded by a large scale magnetic field connected to the BH. We performed global particle-in-cell simulations to capture the dynamics of the electromagnetic fields and of the pair plasma in the corona. We find that a hybrid magnetic topology develops with: (i) magnetic loops connecting the disk to the event horizon, which enables energy and angular momentum exchanges between the 2 components, (ii) open field lines threading the horizon and funneling a Blandford-Znajek jet, and (iii) open magnetic field lines anchored in the disk and inclined enough to launch a magneto-centrifugal wind. Although the corona is essentially force-free, a Y-point at the intersection of these 3 regions seeds a current sheet where magnetic reconnection form macroscopic plasmoids and accelerates particles up to relativistic speeds. It provides a mechanism for variable non-thermal high energy emission. Eventually, I will show particle energy distribution along with synthetic images and spectra.

Speaker: Ileyk El Mellah (IPAG - CNRS)

ID295-EL_MELLAH_BH_disk_coupling.pptx

17:30 A unified picture for three different cosmic-ray observables

We present here a unified scenario that connects together three peculiar spectral features recently reported in the spectra of charged cosmic rays (CRs). The hadronic spectral hardening above $\sim 250 \, \mathrm{GV}$ is here interpreted as a diffusion imprint, and modeled by means of a transport coefficient that smoothly hardens with rigidity. We implement such a propagation framework to solve the transport equation with the DRAGON2 numerical code in order to determine the large-scale contribution to the CR fluxes. On top of this solution we explore the hypothesis of a nearby, hidden Supernova Remnant (SNR) to be responsible for the high-energy (above $\sim 100 \, \mathrm{GeV}$) all-lepton flux, in particular for the spectral break observed around $1 \, \mathrm{TeV}$. We compute such contribution analytically adopting the same propagation setup implemented for the large-scale background. Simultaneously, we find the signature of the same source in the peculiar bump structure observed by the DAMPE Collaboration in the proton spectrum, consisting of a strong hardening at $\sim 500 \, \mathrm{GeV}$ and a softening at $\sim 13 \, \mathrm{TeV}$. We validate our hypothesis with the CR dipole-anisotropy (DA) amplitude and phase, and find that the observations below $\sim 10 \, \mathrm{TeV}$ can be considered as a signature of the nearby SNR that we invoke. If confirmed, our modelling strongly constrains the propagation parameters of the charged particles in our Galaxy and sets the ground for the understanding of the high-energy $\gamma$-ray observations of the forthcoming years.

Speaker: Ottavio Fornieri (GSSI)

ID334_OttavioFornieri_CRLocal.key

ID334_OttavioFornieri_CRLocal.pdf

17:45 Revisiting particle acceleration at ultra-relativistic shocks

Relativistic shocks are thought to drive the non-thermal gamma-ray emission in many astrophysical phenomena, such as GRBs and AGNs. The details of the mechanisms by which particles are accelerated to the energies required to emit gamma rays is not fully understood. Fermi acceleration at relativistic shocks relies on the the particles' ability to repeatedly cross the shock. As argued in previous studies, for acceleration to proceed, the isotropization rate in downstream must exceed the gyro-frequency. This provides an upper limit on the maximum energy, commonly referred to as the magnetized limit.

In this work, we demonstrate that the magnetization limit is in fact a weak condition, and that the maximum energy achievable at a relativistic shock can in fact exceed this limit. We discuss the implications in light of recent TeV detection of GRBs.

Speaker: Zhi-Qiu Huang (Max-Planck-Institut für Kernphysik)

ID360_ZhiqiuHuang_acceleration_relativistic_shock.pdf

ID360_ZhiqiuHuang_acceleration_relativistic_shock.pptx

18:00 Magnetic field amplification driven by the relativistic shock-clump interaction

Magnetic field amplification in collisionless shocks is required for particle acceleration and high-energy synchrotron emission in high-energy astrophysical phenomena. Recent magnetohydrodynamics (MHD) simulations of shocks propagating into inhomogeneous media show that the ambient magnetic field is amplified by turbulent dynamo in the downstream region. However, post-shock density fluctuations could easily decline in a collisionless shock due to particle diffusion, so that it is not clear whether the turbulent dynamo is driven. We investigate the interaction between a relativistic magnetized collisionless shock and a dense clump by means of Particle-in-Cell (PIC) simulation for the first time. We also perform MHD simulations for the same physical condition as the PIC simulation. The PIC simulation shows that particles escape from the dense clump along the magnetic field line. As a result, the vorticity around the shocked clump is smaller than that in the MHD simulations. Moreover, in both PIC and MHD simulations, it is found that the shocked clump quickly decelerates. Because of the escape and the deceleration, the turbulent dynamo driven by the shock-clump interaction is not efficient for relativistic collisionless shocks.

Speaker: Sara TOMITA (Tohoku University)

ID417_sara-tomita_magnetic-field-amplification.pdf

ID417_sara-tomita_magnetic-field-amplification.pptx

18:15 On the role of galactic wind termination shocks in accelerating cosmic rays

The origin of cosmic rays above the \textit{knee} at PeV energies is an unsolved problem. We examine whether the re-acceleration of Galactic cosmic rays at the termination shock developed by the Galactic wind can contribute to the observed spectrum beyond the knee. In particular, in the context of a cosmic-ray-driven galactic wind we study the transport of cosmic rays up to the Galactic wind termination shock, where the re-acceleration occurs through diffusive shock acceleration. We find that the re-accelerated particles can achieve rigidities up to several tens of PV/c and can propagate back to the Galactic disk, potentially contributing to the measured spectrum. We show that the re-accelerated component can contribute to $\sim 10\%$ of the observed all-particle spectrum under standard parametric assumption and up to $\sim$ 40--50\% when optimistic configurations are considered. We finally compute the escaping flux of re-accelerated particles seeding the intergalactic medium with protons of energies up to $\sim$ 100 PeV, and heavier nuclei with energies up to $\sim$ 1 EeV. Finally we explore the associated multimessenger flux in terms of gamma rays and neutrinos resulting from the hadronic interactions of re-accelerated cosmic rays in the whole Galactic wind volume.

Speaker: Payel Mukhopadhyay (Stanford University)

gamma_2022 (2).pdf

20:00 → 23:00 Conference Dinner

Thursday 7 July

09:30 → 10:15 Review Talks: Thursday (Aula Magna Biologia) Chair: Andreas Zech

09:30 Multi-messenger High-Energy Astrophysics results

I will discuss some selected instruments, which are key for current multi-messenger results. Then I will focus on diffuse fluxes, namely the cosmogenic fluxes and galaxy fluxes, which can be better estimated through multiple messengers. I will look into more detail to some galactic sources probable cosmic-ray-gamma-ray-neutrino messengers. On extragalactic sources, I will review recent IceCube results on blazars and starburst galaxies. Finally GRBs as sources connecting gamma-rays and GWs and possibly in the future neutrinos.

Speaker: Teresa Montaruli (Universite de Geneve)

Gamma2022_Montaruli_final.pdf

10:15 → 11:05 Highlight Talks topical: Thursday (Aula Magna Biologia) Chair: Andreas Zech

10:15 Multi-wavelength Astronomy with Gravitational Waves

On 2017 August 17, the merger of a binary neutron-star system observed through gravitational waves and multi-wavelength emission from gamma rays, X-ray, ultraviolet-optical-near infrared, to radio marked the history of multi-messenger astronomy, showing its tremendous potential probe the physics of the most energetic events of the Universe. Multi-messenger discoveries are unveiling the rich physics of neutron star mergers in association with gamma-ray bursts and kilonovae, probing relativistic astrophysics, nuclear physics, nucleosynthesis, and cosmology. This talk will give an overview of observational challenges and perspectives of the multi-wavelength follow-up of gravitational-wave sources based on the current knowledge of the electromagnetic counterparts.

Speaker: Marica Branchesi (Gran Sasso Science Institute/INFN)

GAMMA2022_MBranchesi.pptx

10:40 The Latest Discoveries in High Energy Neutrino Astrophysics

Current knowledge of the Universe is based on information carried by electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. For over a century, scientists have observed cosmic rays, but the understanding of their place of production is limited. As a product of cosmic ray interaction, neutrinos can shed light on the extreme part of the Universe. IceCube Neutrino Observatory has been leading neutrino astronomy research over the last ten years and is the only observatory with the exposure to detect high-energy neutrinos beyond Earth's atmosphere. This presentation will highlight the IceCube observations, including new recent results. Despite the exiting times, with IceCube operating alone and limited by the South Pole location and cubic-km scale, the neutrino astronomy efforts have yet to advance the field past infancy. It is clear that more observatories and larger telescopes, ultimately linked via a global network, are needed to advance fundamental discoveries in astro and particle physics. In this direction, a new opportunity has emerged over the last years to construct a new large volume neutrino telescope, the Pacific Ocean Neutrino Experiment (P-ONE), which will be based for the first time, within an existing oceanographic infrastructure. I will summarize how we have established a scientific relationship with Ocean Networks Canada to pioneer their global network as a testbed infrastructure and identified the optimal location and prepared the ground for the first case deployment.

Speaker: Elisa Resconi (Technical University of Munich)

gamma-2022-Resconi.pdf

11:05 → 11:30 coffee break

11:30 → 12:45 Highlight Talks topical: Thursday (Aula Magna Biologia) Chair: Samar Safi-Harb

11:30 Pulsar Wind Nebulae

Pulsar wind nebulae (PWNe) are multi-wavelength bright sources produced by the interaction of the relativistic, magnetized and cold plasma emanating from the neutron star with the surrounding material, either the ejecta of the supernova explosion or the interstellar medium, depending on their phase of evolution.
They will constitute the widest class of Galactic gamma-ray sources of future surveys, with around 300 new detections expected in the first Galactic Plane Survey of the Cherenkov Telescope Array.
Moreover PWNe are known to be efficient particle accelerators, with the class prototype, the Crab nebula, the unique firmly identified leptonic PeVatron of the Galaxy.
Last years observations at X-rays and gamma-rays have proved they efficiently release particles in the ambient medium in their late evolutionary phases, being connected to the formation of elongated X-ray jets and extended TeV halos.
Almost all the LHAASO's recently detected PeVatrons have a pulsar in their surroundings, leaving open the possibility that all of them are actually illuminated by a pulsar or a pulsar wind nebula that is not resolved by LHAASO.
Being able to model and identify these sources through their different evolutionary stages is then extremely important for the interpretation of future gamma-ray data. Here I will discuss where we are in this respect.

Speaker: Barbara Olmi

BOlmi_gamma2022.pdf

11:55 Recent Results in Supernova Remnants at Highest Energies

Supernova remnants (SNRs) are now established as cosmic particle accelerators through observations of non-thermal emissions from radio to gamma-ray domain in the past decades. In the context of Galactic cosmic-ray origin, one of the key questions was if they are proton accelerators. At least for some SNRs, gamma-ray emissions are solidly attributed to decay of neutral pions, providing long-awaited evidence for proton acceleration. The next and current burning question is if SNRs are accelerators up to the knee at ~ PeV. I will review recent gamma-ray results with particular emphasis on this topic. Information from other wavelengths is essential for this topic as well. X-rays work as probes for electrons accelerated up to very high energies. Synchrotron X-ray variability, if attributed to amplified magnetic fields, gives important information in discussing maximum attainable energies of particles accelerated in SNRs. Interstellar gas clouds observed with radio line emissions not only serve as targets for accelerated protons to produce neutral pions, but also amplify magnetic fields through shock-cloud interactions. I will also review recent X-ray and radio observational results related to particle acceleration in SNRs.

Speaker: Takaaki Tanaka (Konan University)

ID504_TakaTanaka_SNR.pdf

12:20 Relativistic Reconnection

In the most powerful astrophysical sources, reconnection and turbulence operate in the “relativistic” regime, where the magnetic field energy exceeds even the rest mass energy of the plasma. Here, reconnection and turbulence can lead to fast dissipation rates and efficient particle acceleration, thus being prime candidates for powering the observed fast and bright flares of high-energy non-thermal emission. With fully-kinetic particle-in-cell (PIC) simulations and analytical theory, we investigate the physics of relativistic reconnection and turbulence, and demonstrate that they can be the “engines” behind: (1) high-energy flares in blazar jets; and (2) the hard-state spectra of black hole X-ray binaries and Active Galactic Nuclei.

Speaker: Lorenzo Sironi (Columbia University)

barcelona_22_LSironi.key

12:45 → 13:15 POSTER time

13:15 → 15:00 lunch break

15:00 → 16:30 Contributed Talks: EGAL parallel 6 (Aula Magna Ciències de la Terra) Chair: Matteo Cerruti

15:00 High energy neutrinos from gamma-ray bursts

Due to their non-thermal nature, gamma-ray bursts (GRBs) are promising sources of high energy neutrinos. After the years of the GRB triggered search, IceCube Collaboration has put strict upper limits on the neutrino flux. We propose new weighting technique for the neutrino search considering multi-GRB stacking analysis. We invoke known GRB spectral-energy correlations to reduce the amount of unknown and model-dependent GRB parameters. With this approach we perform stacking triggered GRB neutrino search with the open access IceCube data. Despite the prompt emission, we show that the late time X-ray transients associated with GRBs could be promising sources of TeV neutrinos. As a result of our analysis, we put constrains on the amount of protons in the GRB jets and draw prospects for the high energy neutrino detectability with the next generation IceCube-2 detector and upcoming gamma- and X-ray telescopes.

Speaker: Gor Oganesyan (Gran Sasso Science Institute)

gamma_2022_Gor_Oganesyan_neutrinos.pdf

15:15 Multi-messenger characterization of Mrk501 during historically low X-ray and γ-ray activity

Blazars are among the most prominent and luminous objects in the γ-ray sky, but the mechanisms and particle populations behind their emission are still far from understood. The two MAGIC telescopes contribute to solving these riddles by regularly monitoring our closest blazars in the very-high-energy (>0.2 TeV, VHE) regime, which is particularly effective when accompanied with observations from other multiwavelength (MWL) instruments.

In this contribution we present the insights gained from our MWL data set of Mrk 501 collected between 2017 to 2020 with additional results gained when extending the data to the time period from 2008 to 2020. For the first time, we can identify significant correlations between the VHE γ-rays and X-rays for Mrk 501 also during very low-activity states as shown in our 4-year data set. Additionally, the measured correlations in both data sets reveal a delay of the radio emission with respect to the HE γ-rays by more than 100 days suggesting that the HE γ-ray emission is located further upstream the radio-bright regions in the jet of Mrk 501. Moreover, from the mid of 2017 to the mid of 2019 a historically low-state in both VHE as well as X-rays can be detected. The emission is stable with a VHE flux of 5% that of the Crab Nebula, as detected by MAGIC. We investigated the nature of this potential baseline emission using our MWL information together with published multi-messenger results from IceCube setting constraints on possible leptonic, lepto-hadronic and purely hadronic emission scenarios. While the stable emission could originate from a standing shock, the more variable emission in the months before the low-state can be attributed to an independent shock region traveling along the jet of Mrk 501.

Speaker: Lea Heckmann (Max-Planck-Institut für Physik, D-80805 München, Germany)

ID354-LeaHeckmann-Mrk501_lowstate.pdf

15:30 Searches for neutrino point sources in the Northern Sky with the IceCube Neutrino Observatory

Since its first discovery in 2013, the IceCube Neutrino Observatory has been studying the properties of a diffuse flux of astrophysical high-energy neutrinos, trying to unveil the enigma of its origin. Using over 9 years of IceCube data reprocessed to the latest detector calibrations, we investigate the Northern Sky for a local excess of high-energy neutrinos over the atmospheric and cosmic background, to be associated with a neutrino point source. Our analysis allows more accurate localization and neutrino flux characterization of the sources compared to previous works, while also improving the discovery potential by up to ~30%. Furthermore, we present an analysis looking for an excess of signal coming from a population of sub-threshold neutrino sources and discuss the implications on the neutrino luminosity and local source density. In this contribution, we report on the most recent results for neutrino point sources in the Northern Sky.

Speaker: Chiara Bellenghi (Technical University Munich)

ID366_ChiaraBellenghi_IceCubeNeutrinoPointSources.pdf

15:45 An Upper Bound for the Neutrino Flux From Jets of Active Galactic Nuclei

We present a bottom-up calculation of the flux of ultra-high energy cosmic rays (UHECRs) and high-energy neutrinos produced by powerful jets of active galactic nuclei (AGNs).
By propagating test particles in 3D relativistic magnetohydrodynamic jet simulations, including a Monte Carlo treatment of sub-grid pitch-angle scattering and attenuation losses due to realistic photon fields, we study the spectrum and composition of the accelerated UHECRs and estimate the amount of neutrinos produced in such sources.
We find that UHECRs are not significantly affected by photodisintegration in AGN jets, consistent with Auger's detection of heavy elements at the highest energies.
Moreover, we present estimates and \emph{upper bounds} for the flux of high-energy neutrinos expected from AGNs.
In particular, we find that:
i) source neutrinos may account for a sizable fraction, or even dominate, the expected flux of cosmogenic neutrinos;
ii) neutrinos from the $\beta$-decay of secondary neutrons produced in nuclei photodisintegration may in principle contribute to the signal observed by IceCube, but can hardly account for all of it;
iii) since the most important background for UHECR--photons interactions is the AGN non-thermal emission, a picture arises where high-energy neutrino emission can correlate with AGN flaring activity.
We discuss our results in the light of multimessenger astronomy and current/future neutrino experiments.

Speaker: Rostom Mbarek (University of Chicago)

Rostom_M_gamma22.key

16:00 High-energy neutrinos and gamma rays from winds and tori in active galactic nuclei

Powerful winds with wide opening angles, likely driven by accretion disks around black holes, are observed in the majority of active galactic nuclei (AGN) and can play a crucial role in AGN and galaxy evolution. If protons can be accelerated in the wind near the black hole, e.g. via diffusive shock acceleration, $p\gamma$ processes with photons from the nucleus generate neutrinos, as well as $\gamma\gamma$ cascade emission from the gamma-ray to radio bands. The TeV neutrinos tentatively detected by IceCube from the obscured Seyfert galaxy NGC 1068 can be interpreted consistently if the shock velocity $\sim$1000 km ${\rm s^{-1}}$, which may correspond to a failed, line-driven wind that is physically well motivated. While the $p\gamma$ cascade is mostly $\gamma\gamma$-attenuated above MeV energies, the GeV photons observed from NGC 1068 and some other radio-quiet AGN may arise from an outer shock where the wind impacts the obscuring torus, e.g. via $pp$ processes, along with some observable radio emission. Observational tests and implications of this scenario are discussed. Neutrinos may offer a unique probe of the launching sites of AGN winds, particularly for objects obscured in photons.

Speaker: Susumu Inoue (Bunkyo U. / RIKEN)

AGNwindtori_Gamma22_SusumuInoue.pdf

16:15 Cosmology, fundamental physics and Multi-Messenger Astrophysics with Gamma-Ray Bursts

Gamma-Ray Bursts constitute one of the most fascinating and relevant phenomena in modern science, with strong implications for several fields of astrophysics, cosmology and fundamental physics. Indeed, the huge luminosity, the redshift distribution extending at least up to z~10 and the association with the explosive death of very massive stars make long GRBs (i.e., those lasting up to a few minutes) potentially extremely powerful probes for investigating the early Universe (pop-III stars, cosmic re-ionization, SFR and metallicity evolution up to the "cosmic dawn") and measuring cosmological parameters. The combination of extreme distances, the huge number of photons emitted over about three orders of magnitude in photon energy and the variability down to few ms makes these phenomena also a uniquely powerful and promising tool for performing tests of fundamental physics like Lorentz Invariance Violation (LIV) with unprecedented accuracy. At the same time, as demonstrated by the GW170817 event, short GRBs (lasting no more than a few s) are the most prominent electromagnetic counterpart of gravitational-wave sources like NS-NS and NS-BH merging events, and both long and short GRBs are expected to be associated with neutrino emission. My review will include the status, concepts and expected performances of space mission projects (e.g, THESEUS, Gamow Explorer) aiming at fully exploiting these unique potentialities of the GRB phenomenon, thus providing an ideal synergy with the large e.m. facilities of the future like LSST, ELT, TMT, SKA, CTA, ATHENA in the e.m. domain, advanced second generation (2G++) and third generation (3G) GW detectors and future large neutrino detectors (e.g., Km3NET).

Speaker: Lorenzo Amati (INAF - OAS Bologna)

ID493-LorenzoAmati-GRB-Cosmo-MMA-Physics.pdf

ID493-LorenzoAmati-GRB-Cosmo-MMA-Physics.pptx

15:00 → 16:40 Contributed Talks: GAL parallel 7 (Aula Magna Biologia) Chair: Masha Chernyakova

15:00 Particle acceleration at pulsar wind termination shocks revisited: shear, reconnection and giant plasmoids

Particle acceleration in relativistic shocks is quenched in the presence of a transverse magnetic field, even for a moderately low upstream magnetization. Pulsar wind nebulae form downstream of an ultra-relativistic magnetized shock; yet these objects are one of the most efficient particle accelerators known in the Galaxy. We propose that the key to this striking discrepancy lies in the anisotropic nature of the magnetic field profile in the pulsar wind. Using particle-in-cell simulations, we show that it has a dramatic impact on the structure and evolution of the shock. The formation of a current sheet in the equatorial plane, combined with a large-scale velocity shear flow lead to strong plasma turbulence and efficient non-thermal particle acceleration near the Bohm limit. The interplay between these processes may power the bright synchrotron nebula surrounding pulsars and possibly the puzzling Crab gamma-ray flares. Another important feature of the predicted shock structure is the presence of hot macroscopic filaments whose formation is driven by reconnection along the equatorial plane. We argue that these compact plasma structures (giant plasmoids) may explain the mysterious knots contained within the Crab Nebula inner ring.

Speaker: Mr Benoît Cerutti (CNRS & Université Grenoble Alpes)

densities_s30_xxl.avi

ID263_bcerutti_Gamma2022_movieless.pdf

ID263_bcerutti_Gamma2022.odp

15:15 Assessing the flaring behaviour of the Crab pulsar wind nebula system in high-energy ranges

The Crab system, a bright pulsar wind nebula powered by the young energetic central pulsar PSR B0531+21, has been extensively observed across the electromagnetic spectrum. Its extreme behaviour in the gamma-ray band has been repetitively challenging our understanding of acceleration mechanisms and radiation processes. Studies have purported a flaring emission associated with the synchrotron process originating from the nebula, in energy ranges below a few hundreds of MeV.
By analysing available Fermi-LAT data across a thirteen-year-long monitoring, we study the energy-dependence and time-variability of the observed high-energy flares in energy ranges up to a few GeV. Moreover we attempt to characterise known and candidate flaring epochs, so as to investigate the short and longer term effect on the presumed steady-state emission of the system. In this presentation we shall focus on the example of selected flares showcasing intriguing spectral evolution. We discuss their observational signature in the context of particle acceleration in the Crab
pulsar wind and consider their limitations on distinguishing competing mechanisms.

Speaker: Michelle Tsirou (MPIK-HD)

Tsirou_et-al_CrabPWN-flares_editor.odp

Tsirou_et-al_CrabPWN-flares.odp

Tsirou_et-al_CrabPWN-flares.pdf

15:30 High-mass gamma-ray binaries as very efficient accelerators

Speaker: Valenti Bosch-Ramon (Universitat de Barcelona/ICCUB)

vbosch.pdf

15:45 ALMA CO Observations in the Northwestern Shell of the Gamma-Ray SNR RX J1713.7-3946

We report on results of CO observations in the northwestern shell of the supernova remnant (SNR) RX J1713.7$-$3946 using the Atacama Large Millimeter/submillimeter Array (ALMA). We recently found dozens of molecular cloudlets with typical radii of $\sim$0.03-0.05 pc and densities of $\sim$$10^4$ cm$^{-3}$, which have survived shock passage due to their high density. These cloudlets are located not only along synchrotron X-ray filaments, but also in the vicinity of X-ray hotspots with month- or year-scale time variations. We argue that X-ray hotspots and filaments were generated by shock-cloudlet interactions through magnetic-field amplification up to mG. The gas density contrast of $\sim$$10^5$, the coexistence of molecular cloudlets and low-density diffuse medium of $\sim$0.1 cm$^{-3}$, is consistent with such a magnetic field amplification and a wind-bubble scenario. The small-scale cloud structures also affect hadronic gamma-ray spectra considering the magnetic field amplification on surface and inside clouds.

Speaker: Hidetoshi Sano (Gifu University)

ID462-HidetoshiSANO-RXJ1713-ALMA-CO_v3.pdf

16:00 Particle escape from supernova remnant shocks: gamma-ray and cosmic-ray signatures

In the context of the supernova remnant (SNR) paradigm for the origin of Galactic cosmic rays (CRs), the escape process of accelerated particles represents a fundamental piece of information to interpret both the observed CR spectrum and the gamma-ray spectral signatures emerging from these sources. Under the assumption that in the spatial region immediately outside of the remnant the diffusion coefficient is suppressed with respect to the average Galactic one, we found that a significant fraction of particles can still be located inside the SNR long time after their nominal release from the acceleration region. This fact results into a gamma-ray spectrum arising from hadronic collisions that resembles a broken power law, similar to those observed in several middle-aged SNRs. Above the break, the spectral steepening is determined by the diffusion coefficient outside of the SNR and by the time dependence of maximum energy. Consequently, the comparison between SNR data and model predictions will possibly allow to determine these two quantities. Additionally, by further assuming that protons and electrons are accelerated at SNR shocks with the same slope, CR spectral measurements on Earth can then be reproduced if electrons are injected with a spectrum steeper than protons for energies above ~ 10 GeV. A possible scenario that can in principle justify the observed steeper electron spectrum relies on the combination of energy losses, due to synchrotron radiation in an amplified magnetic field, and time dependent acceleration efficiency.

Speaker: Silvia Celli (Sapienza University & INFN)

ID475-SilviaCelli_particle_escape_SNRs.pdf

16:15 -

16:30 → 17:00 coffee break

17:00 → 18:30 Contributed Talks: GAL / APFP parallel (Aula Magna Biologia) Chair: Dmitry Khangulyan

17:00 Adiabatic-radiative shock systems in non-relativistic astrophysical jets: a key to enhance the gamma-ray emision

Of all the processes in the Universe, the bipolar ejection of collimated plasma outflows from the inner regions of the accretion disc around a central object are among the most remarkable. The shocks that form in highly supersonic jets are ideal sites for particle acceleration. By combining multi-wavelength observational data, numerical simulations, and plasma physics we study diffusive shock acceleration and gamma-ray emission in jets in protostars and supersonic outflows in classical novae. The coexistence of an adiabatic and a radiative shock is expected in the jet termination region, being this scenario very promising for particle acceleration and high-energy emission. Particles accelerated in the adiabatic shock can radiate through proton-proton collisions and relativistic Bremsstrahlung in the dense layer separating the adiabatic and radiative shock downstream regions. We find that protostellar jets can reach detectable levels of gamma-ray emission in this framework, not detected to date. Nova outflows have been detected in the gamma-ray domain, and we propose here an alternative scenario to explain the high-energy emission. Furthermore, the parameters for scaled laboratory experiments are very much in line with plasma conditions achievable in high-power laser facilities opening the door to new means for studying novae outflows never considered before.

Speaker: Anabella Araudo

Gamma_22.pdf

17:15 PWNe beyond the free expansion

It is known that CTA will contribute to the discovery of tens or hundreds of new pulsar wind nebulae (PWNe). Many of them will be beyond the free expansion phase, thus it is necessary to study in detail what is their evolution across this phase. The current one-zone models for PWNe treat the nebulae and the supernova remnant (SNR) as an uniform system and important mismatches appear when we simulate and compare the SNR pressure outside the PWN shell with 1D hydrodynamic (HD) models during the reverberation phase where, after the arrival of the reverse shock, the shocked material of the SNR directly interacts with the PWN shell. We use TIDE, an advanced radiative code, to evaluate the impact of various parameters (properties of the supernova ejecta, inner pulsar and ambient medium) upon the extent of the reverberation phase of PWNe in properties as the starting time of the reverberation phase and how this affects the amount of the compression, and how much of this can be ascribable to the radiation processes. We also provide a new prescription for the SNR shock trajectories, updating the work already done by Truelove & McKee in 1999, with the final aim of providing a new set of semi-analytical equations to model the reverberation phase in one-zone models with 1D-HD-simulations-like accuracy.

Speaker: Jonatan Martin (Osservatorio Astrofisico di Arcetri (INAF))

gamma2022_martin.pdf

17:30 Making sense of recent results on electrons and positrons from cosmic ray experiments

The new AMS-02 measurements of the cosmic-ray (CR) electron and positron energy spectra have provided spectacular confirmation of the earlier claim by PAMELA and FERMI of a rising positron-over-electron fraction and, for the first time, have identified a sharp drop-off of the positron flux above ~300 GeV and a tiny change of the electron slope at ~40 GeV. At the same time, HESS, CALET and DAMPE have reported substantial steepening of the total lepton spectrum at ∼TeV with a spectral index softening by about 1.
I will present the results of a novel calculation of the flux of electrons and positrons as produced by SNRs, Pulsar Wind Nebulae (PWN) and secondary interactions of CRs in the Galaxy. In particular, I will show under which conditions for the injection and transport of these particles the reported spectral features can be consistently reproduced and I will discuss the connection with the recent detection of extended “Tev Halos” around Pulsars.
Finally, I will review the consequences of the stochasticity in the occurrence of source events specifically if these are correlated with the spiral arms of the Galaxy, and I will oppose the scenario in which the observed features are the effect of prominent nearby sources.

Speaker: Carmelo Evoli (Gran Sasso Science Institute)

ID263-CarmeloEvoli-Cosmic_ray_leptons.pdf

17:45 Gamma-ray monochromatic line emission search from dark matter annihilation up to 100 TeV towards the Galactic Centre with MAGIC

The detection of line-like TeV gamma-ray features configures as a smoking gun for the discovery of TeV-scale particle dark matter. We report the first search for dark matter spectral lines in the Galactic Centre region up to gamma-ray energies of 100 TeV with the MAGIC telescopes (La Palma, Canary Islands). The Galactic Centre region is expected to host the most promising dark matter halo due to its size and proximity and is therefore well suited for this kind of searches. Observations at large zenith angles improve sensitivity for gamma-rays in the TeV regime due to the increased telescope collection area. We present the results obtained with more than 200 hours of large-zenith angle observations of the Galactic Centre region, which allow us to obtain competitive limits to the dark matter annihilation cross-section at high particle masses (< $5×10^{-28}$ $\mathrm{cm^3 s^{-1}}$ at 1 TeV and < $1×10^{-25}$ $\mathrm{cm^3}$ $\mathrm{s}^{-1}$ at 100 TeV), improving the best current constraints above 20 TeV. In addition, we also study the impact of an inner cored dark matter halo on probing the annihilation cross-section. Finally, we use the derived limits to constrain super-symmetric wino models.

Speaker: Tomohiro Inada (ICRR, UTokyo)

Gamma_GCDM_MAGIC_Inada.pdf

18:00 Search for Dark Matter annihilation with a combined analysis of dwarf spheroidal galaxies from Fermi-LAT, HAWC, H.E.S.S., MAGIC and VERITAS

Dwarf spheroidal galaxies (dSphs) are among the most dark matter (DM) dominated objects with negligible expected astrophysical gamma-ray emission. This makes nearby dSphs ideal targets for indirect searches of a DM particle signal. The accurate knowledge of their DM content makes it possible to derive robust constraints on the velocity-weighted cross section of DM annihilation. We report on a joint analysis of 20 dSphs observed by Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS in order to maximize the sensitivity of DM searches towards such targets, using a common maximum likelihood approach. Results for seven annihilation channels and spanning a range of DM masses from 5 GeV to 100 TeV will be presented. Furthermore, the systematic uncertainties coming from the astrophysical J-factor calculated from the dSph dark matter distribution will be discussed by comparing results obtained from two different sets of J-factors.

Speaker: Daniel Kerszberg (IFAE-BIST)

Gamma_Barcelona_DM_07072022_v2_Kerszberg.pdf

18:15 LIVelihood: Testing Lorentz Invariance Violation on Observations of Energy-dependent Time Delays from Multiple-type Gamma-ray Sources

Some Quantum Gravity (QG) models allow Lorentz Invariance Violation (LIV) to emerge at the order of the Planck energy (~10^19 GeV). A possible consequence of LIV is the energy-dependent speed of light. This hypothesis can be tested using high energy gamma-ray observations of highly variable and distant sources, by measuring time lag of high energetic events. Imaging Atmospheric Cherenkov Telescopes detect Gamma-Ray Bursts (GRB), flaring Active Galatic Nuclei (AGN) and pulsars up to tens of TeV, which opens an interesting window to explore time lag at high energy. The three major IACTs experiments, H.E.S.S., MAGIC and VERITAS have formed a working group to combine all the relevant data collected in order to constrain the energy scale of LIV. In our contribution, we will present the first results of this working group and the code that was created to handle data from various observatories called LIVelihood.The LIVelihood code uses a likelihood method to analyse these different datasets and is made to perform combination of data from different observatories taking into account their respective Instrumental Response Function (IRF) and systematical uncertainties. The main features and the first results of this code will be exhibit on the combination of data from various gamma-ray observatories. The future steps for the LIVelihood code development and the combination of gamma-ray observatories will be announced.

Speaker: Sami Caroff (LAPP)

LIVelihood: Testing Lorentz Invariance Violation on Observations of Energy-dependent Time Delays from Multiple-type Gamma-ray Sources

17:00 → 18:30 Contributed Talks: INSTR parallel (Aula Magna Ciències de la Terra) Chair: Abelardo Moralejo

17:00 The ASTRI Mini-Array Core Science Program

Celestial sources emitting at high-energy (HE, E>100 MeV) and at very high-energy (VHE, E>100 GeV) are of the order of a few thousands and a few hundreds, respectively. On the other hand, the number of sources emitting at ultra high-energy (UHE, E> several tens of TeV) are just a few dozens, and are currently being investigated by means of both ground-based imaging atmospheric Cherenkov telescopes (IACTs) and particle shower arrays. These rare VHE and UHE sources represent a new frontier in astrophysics. An array composed of nine ASTRI Cherenkov telescopes is under construction at the Observatorio del Teide (Tenerife, Spain). The ASTRI Mini-Array aims at providing robust answers to a few selected open questions in the VHE and UHE domains. The scientific program during the first four observing years will be devoted to the following Core Science topics: the origin of cosmic rays, the extra-galactic background light and the study of fundamental physics, the novel field in the VHE domain of gamma-ray bursts and multi-messenger transients, and finally the usage of the ASTRI Mini-Array to investigate ultra high-energy cosmic rays and to undertake stellar intensity interferometry studies. We review the scientific prospects assessed through dedicated simulations, proving the potential of the ASTRI Mini-Array in pursuing breakthrough discoveries and discuss the synergies with current and future VHE facilities in the Northern hemisphere, such as MAGIC, LHAASO, HAWC, Tibet AS-gamma, and CTAO-N.

Speaker: Stefano Vercellone (INAF-OAB)

ID348-StefanoVercellone-ASTRI_Core_Science.pdf

17:15 The SST-1M gamma-ray mini-array - early operations and prospects

We present first results of the commissioning data from two Single-Mirror Small-Sized Telescopes (SST-1M) for gamma-ray detection with imaging air Cherenkov technique. SST-1M adopts a Davies-Cotton optics and a fully digitising silicon photomultipliers (SiPM) based camera. SST-1M telescopes have a lightweight and compact structure with 4 m-diameter mirror dish composed of 18 hexagonal glass mirrors and the focal ratio of 1.4. It has a wide field-of-view of 9.1◦. The innovative cameras employ digital electronics, with fully digital trigger and readout architecture, and highly performing large-area SiPM with dedicated slow control. The SST-1M telescopes are optimized to provide gamma-ray sensitivity above 500 GeV in stereo mode. They already allow fully robotic operation and they are designed for operation in harsh environment with minimal maintenance. The SST-1M mini-array is installed at the Ondřejov Observatory in the Czech Republic and undergoes commissioning and validation during which first remote observations of astronomical sources are performed. In our presentation we will report on the status of the project and present first results of early science operations.

Speaker: Jacek Niemiec (Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland)

ID359_JacekNiemiec_SST-1M.pdf

17:30 Advancing the atmospheric Cherenkov-method to detect gamma-rays with one Giga electron Volt

Imaging atmospheric Cherenkov-telescopes are powerful detectors for cosmic gamma-rays. Yet the detection of gamma-rays with lower energies in the domain of Giga electron Volts (so far reserved to satellites) at the high rates provided by the large collective area of the atmospheric Cherenkov-method, can be a potential advance. This will improve our understanding of short lived transients and of distant sources which have their gamma-rays with higher energies absorbed by infrared light. With telescopes, the detection of gamma-rays with lower energies implies larger mirrors, which narrow the depth-of-field, and blur the image. Larger mirrors imply an exponential increase in costs to prevent deformations of the optics. In addition, the mirror’s aberrations further blur the image and limit the field-of-view. To advance, we propose a new class of instrument (the Cherenkov-plenoscope) which senses not only the direction of Cherenkov-photons but also their point of reflection on the mirror. The Cherenkov-plenoscope turns a narrow depth-of-field into the perception of depth, compensates deformations, and compensates the mirror's aberrations. We will discuss the possibility of a Cherenkov-plenoscope dedicated to the detection of gamma-rays with energies as low as one Giga electron Volt, and our current estimate of its capabilities.

Speaker: Sebastian Achim Mueller (Max Planck Institute for Nuclear Physics)

resources

• Cherenkov-plenoscope_on_github.png
• did_you_say_seventtyone_meters.png
• where_it_all_began.jpg

talk ID353_sebastian_achim_mueller_gamma2022_advancing_the_atmospheric_cherenkov_method_v2.pdf

talk_rendered_to_jpg ID353_JPG_sebastian_achim_mueller_gamma2022_advancing_the_atmospheric_cherenkov_method_v2.pdf

talk_with_speech ID353-SPEECH_sebastian_achim_mueller_gamma2022_advancing_the_atmospheric_cherenkov_method_v2.pdf

17:45 Gammapy - an open source package for high energy astrophysics

Gammapy, an open source python package selected as the CTA Science tools, is a community-developed, open source Python package built on Numpy, Scipy and Astropy using open FITS based data formats. It is used for the analysis of gamma-ray data of many instruments including Imaging Atmospheric Cherenkov Telescopes (IACT; eg: CTA, H.E.S.S. and MAGIC), Water Cherenkov Detectors (WCD; eg: HAWC), as well as space based observatories (eg: Fermi-LAT).

Starting from event list and instrument response functions at the so called "Data Level 3", gammapy provides pipelines for reduction of the input data to binned WCS, HEALPix or region based data structures. A variety of background reduction methods, including traditional techniques like the Reflected and Ring regions, as well as novel 3D Field of View Likelihood techniques, are supported. Counts, background and IRFs data are bundled in datasets ("Data Level 3") and can be serialised, rebinned and stacked.

Modelling of datasets are supported using Poisson maximum likelihood fitting. While a variety of in-built spectral, temporal and spatial models are supplied, it also supports custom user defined models, eg: energy dependent morphology for galactic accelerators or temporal models with spectroscopic variability for blazars. Moreover, it enables joint likelihood analysis between different datasets, thus providing a simple platform for handling time dependent instrument response, different classes of events, or performing a combined multi-instrument analysis. Gammapy also implements methods to estimate flux points, including likelihood profiles per energy bin, light curves as well as flux and signficance maps in energy bins

Gammapy is heavily in development, and new features are added every few months. This contribution will present and overview of the package, describing the development history and future plans towards a stable release, and also demonstrate some key analysis features using H.E.S.S, Fermi-LAT and simulated CTA data.

Speaker: Atreyee Sinha (UCM, Madrid)

ID479_AtreyeeSinha_Gammapy.pdf

18:00 Establishing the MAGIC data legacy: adopting standardised data formats and open-source analysis tools

The open data access that will be provided by the next generation of gamma-ray observatories has encouraged the development of standardised data formats and open-source analysis software. Many recent publications have demonstrated the applicability of the specifications proposed by the community-driven "Data formats for gamma-ray astronomy" (GADF) initiative to ground-based gamma-ray instrument data. They have also validated the analysis of GADF-compliant data with open-source analysis tools such as Gammapy.

In this contribution, we present the effort to adopt the same specifications for the data taken with the MAGIC telescopes. We reproduce results from the literature for some reference sources, validating the Gammapy analysis against results obtained with the MAGIC closed-source software, MARS. The adoption of these standardized data formats and open-source science tools by the MAGIC Collaboration for its scientific analyses marks an important milestone in building a data legacy for its two decades of observations.

Speaker: Cosimo Nigro (Institut de Física d'Altes Energies (IFAE))

id_305_magic_data_legacy_gamma_2022_cosimo_nigro.pdf

18:15 Astro-COLIBRI: The coincidence library for real-time inquiry for multi-messenger astrophysics

Astro-COLIBRI is a novel tool that evaluates alerts of transient observations in real time, filters them by user-specified criteria, and puts them into their multiwavelength and multimessenger context. Astro-COLIBRI is a fast and easily readable software that contributes to an enhanced discovery potential of both serendipitous and follow-up observations of the transient sky.

In this talk, the key features of Astro-COLIBRI are presented. We'll outline the architecture and present the version 2.0 of the web front end. The platform being live, some use cases will also be presented showing the search for high-energy gamma-ray counterparts to high-energy neutrinos, gamma-ray bursts and gravitational waves. Astro COLIBRI is available on IOS and Android.

Speaker: Valentin lefranc (CEA IRFU)

Astro-COLIBRI_2022-07-07.pdf

Friday 8 July

09:30 → 11:10 Invited Talks (Aula Magna Biologia) Chair: Stefano Vercellone

09:30 CTA Science in the multimessenger era

High-energy photons are a powerful tool to understand the most violent phenomena in our Universe. Space instruments, as well as ground-based ones, are now producing a steady flow of important results often in conjunction with observatories working at different wavelengths. Multi-messenger astronomy is the newly born discipline to which high-energy gamma-ray detectors provide an essential contribution. Indeed high-energy gamma-rays provide a natural link between electromagnetic astronomy and gravitational as well as neutrino ones. Although high-energy astrophysics is enjoying a true golden age, not all the long-standing problems have been solved. The origin of cosmic rays is still challenging us. To pinpoint the ultimate accelerators sky coverage, together with sensitivity and high angular resolution are badly needed. The Cherenkov Telescope Array promises to be a game changer and we are eagerly waiting for it.

Speaker: Patrizia Caraveo (IASF-INAF)

CTA_Caraveo-multi.pptx

09:50 CTAO Overview

Very-high-energy (VHE) gamma-ray astroparticle physics is a relatively young field, and observations over the past decade have surprisingly revealed almost 250 VHE emitters which appear to act as cosmic particle accelerators. These sources are an important component of the Universe, influencing the evolution of stars and galaxies. At the same time, they also act as a probe of physics in the most extreme environments known - such as in supernova explosions, and around or after the merging of black holes and neutron stars. However, the existing experiments have provided exciting glimpses, but often falling short of supplying the full answer. A deeper understanding of the TeV sky requires a significant improvement in sensitivity at TeV energies, a wider energy coverage from tens of GeV to hundreds of TeV and a much better angular and energy resolution with respect to the currently running facilities. The next generation gamma-ray observatory, the Cherenkov Telescope Array Observatory (CTAO), is the answer to this need. In this talk I will present this upcoming observatory from its design to the construction, and its potential science exploitation. CTAO will allow the entire astronomical community to explore a new discovery space that will likely lead to paradigm-changing breakthroughs. In particular, CTAO has an unprecedented sensitivity to short (sub-minute) timescale phenomena, placing it as a key instrument in the future of multi-messenger and multi-wavelength time domain astronomy.

Speaker: Chiara Righi (INAF O.A. Brera)

20220708_v6.pdf

10:10 Status of LST project

Thanks to their large reflectors and improved photon collection efficiency, the Large-Sized Telescopes (LSTs) of the Cherenkov Telescope Array (CTA) target the lowest gamma-ray energies observable from the ground, down to 20 GeV. A four LST sub-array is currently under construction at the CTA-North site of La Palma (Spain). The first LST, LST1, in fact was already inaugurated in 2018. I will report on the progress of the LST project in general and review the early science that LST1 is delivering during its commissioning phase.

Speaker: Juan Cortina (CIEMAT)

Gamma2022_JCortina_LST_status_v5.pdf

10:30 Status of ASTRI Project

We will describe the current status of the ASTRI Mini-Array, under construction at the Teide Astronomical Observatory in Tenerife, Spain. The final layout of the array will include 9 small Cherenkov telescopes covering an area of about 650 x 270 square meters. The ASTRI telescopes adopt a dual-mirror Schwarzchild-Couder optical design. In the focal plane, the ASTRI camera, based on silicon photon-multipliers detectors, will cover a large field-of-view (∼10 deg in diameter). This system provides a good gamma-ray sensitivity also at very high energies (VHE, above 100 TeV) and large off-axis angles (up to ~5 degrees), combined with a good angular resolution.
The scientific goals of the ASTRI Mini-Array include spectral and morphological characterization of the LHAASO sources and other Pevatron candidates, studies of PWNe and TeV halos, Blazar monitoring at VHE, fundamental physics and follow-up of transient events. The beginning of the scientific operations is planned in late 2024. The first 3 years will be dedicated to the core science and the ASTRI Mini-Array will be run as an experiment. During the following years it will gradually move towards an observatory model, open to the community.

Speaker: Andrea Giuliani (INAF - IASF Milano)

Giuliani_ASTRIstatus.pdf

10:50 Status of SWGO Project

The HAWC and LHAASO observatories have demonstrated the power of ground-level particle detection for very high energy gamma-ray astronomy. The wide-field and high duty cycle nature of this approach is highly complementatary to the more well-established imaging atmospheric Cherenkov Technique technique. The Southern Wide-field Gamma-ray Observatory (SWGO) is a global effort towards a next generation observatory of this type, to be located in the Andes of South America. SWGO is targetting transient astrophysics, large-scale diffuse emission and ultra-high energy emission. As the first instrument of its type in the southern hemisphere there is huge discovery potential, and SWGO will strongly complement the CTA Southern Array to be built in Chile. The project is currently in an R&D phase but the international collaboration is now well established and major design decisions and site choice are on the horizon. In this presentation I will discuss the science goals and the current status and timeline of the project.

Speaker: Jim Hinton (MPIK Heidelberg)

SWGO-Barcelona.pdf

SWGO-Barcelona.pptx

11:10 → 11:40 coffee break

11:40 → 12:40 Reports (Aula Magna Biologia) Chair: Josep M. Paredes

11:40 Rapporteur: Galactic Science

Speaker: Marc Ribó (mribo@fqa.ub.edu)

Marc_Ribo_Rapporteur_Galactic_Science.pdf

12:10 Rapporteur: Extragalactic Science

Speaker: Reshmi Mukherjee (Barnard College, Columbia University)

ID258_Gamma2022_Reshmi_Mukherjee_Extragalactic.pdf

12:40 → 12:55 Closing Remarks (Aula Magna Biologia) Josep Maria Paredes and Felix Aharonian