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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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....
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...
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....
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...
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,...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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,...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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.
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...
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....
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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,...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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,...
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...
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...
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...
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...
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...
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...
We reports the results of a composite analysis of the pulsar wind nebula (PWN) around PSR B1853+01 using archival data from $\textit{Chandra}$, XMM-$\textit{Newton}$ and NuSTAR. Both images from $\textit{Chandra}$ and XMM-$\textit{Newton}$ in hard X-rays (>2 KeV) show a PWN consisting of an extended tail-like structure trailing the pulsar and an unorthodox diffuse antennae-like feature ahead...
The study of pulsar magnetospheres has developed quickly in recent years thanks to the development of high-performance computing. Two complementary numerical methods have been used to model these objects thus far: the magnetohydrodynamic (MHD) and the particle-in-cell (PIC) techniques. The MHD approach is well-suited to describe the plasma at large scales, while the PIC method is appropriate...
SS433 is a galactic microquasar with powerful outflows, originated in jets, accretion disk and winds, with well known orbital, precessional and nutational periods. In this work we present a characterization of different outflows parameters throughout the precessional cycle of the system, by analyzing 10 NuSTAR (3–70 keV) observations of ∼30 ks that span ∼1.5 precessional cycles. We have...
We have present properties like inclination angle, dust color temperature, and dust mass of core region in far-infrared located nearby White dwarf WD2236+541. The size of the cavity is 0.84 pc×0.51 pc. The cavity is formed by high pressure at the time of white dwarf formation. The dust color temperature varies from 22.42K to 27.43 K. The inclination angle of the cavity is 54.2°. The position...
Using data from the WISE all-sky survey we discovered that the non-thermal infrared emission of blazars, the largest known population of extragalactic gamma-ray sources, has peculiar spectral properties. Here I will review all results achieved on the well known "infrared-gamma-ray connection" based on the latest releases available for both the WISE and the Fermi source catalogs. I will show an...
The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is a wide-field of view and high-duty cycle detector sensitive to photons of energies between ~0.3 and ~300 TeV. HAWC has been able to detect several sources from extragalactic origin. In this work we present the results of the search of active galactic nuclei from the Third Catalog of Hard Fermi-LAT sources using more than 1500...
Night Sky Background (NSB) is a complex phenomenon, consisting of all light detected by
imaging atmospheric Cherenkov telescopes not attributable to Cherenkov light emission.
Understanding the effect of NSB on cameras for the next-generation Cherenkov Telescope
Array (CTA) is important, as it affects the astrophysical systematic errors on observations,
the energy threshold, the thermal...
In recent years, jetted AGN have been increasingly studied in extensive multi-wavelength campaigns, sampling their emission from radio up to very-high-energies gamma rays. The amount of data gathered calls for the modelling effort to be open to a wide number of astrophysicists.
In this contribution we present agnpy, an open-source python package modelling the radiative processes of...
Recently, ground-based Imaging Atmospheric Cherenkov Telescopes, such as MAGIC and H.E.S.S., have reported the detection of very-high-energy (VHE) gamma-rays from four gamma-ray bursts (GRB 180720B, 190114C, 190829A, 201216C). One of them, GRB 190829A, was triggered by the Swift satellite, and about 20000 s after the burst onset the VHE gamma-ray emission was detected by H.E.S.S. with ~ 20...
TeV halos have become a new class of astrophysical objects which were not predicted before their recent observation. They offer evidence that diffusion around sources (concretely, pulsars) is not compatible with the effective average diffusion that our models predict for the Galaxy. This directly impacts Galaxy formation, our knowledge of the propagation process throughout the Galaxy and our...
BL Lacertae (BL Lac) is categorized as TeV blazar and considered as a possible source of astrophysical neutrinos. In 2020, the brightest X-ray flare ever detected from it. A detailed study can answer many puzzling questions related to multiband emissions and fast-flux variability often seen in this kind of source. We found that the source has crossed all its previous limits of flux and reached...
The diffusive shock acceleration of a population of relativistic electrons on internal shocks is one of the main scenarios to account for the multi-wavelength (MWL) flux variability observed in relativistic jets of active galactic nuclei. In addition to observations of flux variability, constraints are also provided by very-long-baseline interferometry (VLBI), which shows a large variety of...
The Kepler supernova remnant was until recently the only historic supernova remnant lacking a detection at GeV and TeV energies. Using an optimized analysis based on 12 years of Fermi-LAT observations, we report a solid >6σ detection with a spectral index of 2.1 for an energy flux above 100 MeV of $3.1 \times 10^{-12}$ erg.cm$^{−2}$.s$^{−1}$. The gamma-ray excess is fully compatible with the...
Cosmic ray (CR) acceleration processes can be studied by using a fully-kinetic treatment for plasma simulations, e.g., particle-in-cell (PIC) simulations, that allow us to describe a detailed microphysics responsible for CR acceleration. Particle tracing implemented in many PIC codes is able to store full datasets for selected high-energy particles. However, the by-eye inspection of particle...
GRBs (gamma-ray burst) events are one of the highest energy explosions in distant galaxies. Classically GRBs are classified into two classes on the basis of their time duration T(90). Here we have tried to check for the classification of GRBs using Machine Learning algorithms. Specifically, we will study the classification for GRB parameters like T90, T50, and other flux model parameters.
One of the most pressing questions for modern physics is the nature of dark matter (DM). Several efforts have been made to model this elusive kind of matter. The largest fraction of DM cannot be made of any of the known particles of the Standard Model (SM). We focus on brane world theory as a prospective framework for DM candidates beyond the SM of particle physics. The new degrees of freedom...
The first observation of a short Gamma-Ray Burst in association with a Gravitational Wave opened a new era in the high energy astrophysics. The measured T90 of GRB170817A, of about 2 s, reinforces the necessity of a new way of classification. For this reason, we analyse at the Swift-BAT prompt emission data by applying a classification procedure that uses a machine learning technique that...
The open-source Python package Gammapy, developed for the high-level analysis of gamma-ray data, requires gamma-like event lists combined with corresponding instrument response functions. For morphological analysis, this data has to include a background acceptance model. Here we report an approach to generate such a model for the MAGIC telescope data, accounting for the azimuth and zenith...
Gamma-rays and high-energy neutrinos offer complementary ways to study particle acceleration in energetic astrophysical sources. However, analysing these observations together is challenged by possible explanations from a range of complex models, with many uncertainties and observational effects to take into account. We present a coherent data analysis framework based on hierarchical modeling...
Dark Matter (DM) can explain many astrophysical and cosmological measurements. However, its underlying nature remains a mystery. Weakly interacting massive particles (WIMPs) are among the most promising candidates to explain DM. The former have mass and coupling strength at the electroweak scale. If WIMPs are thermally-produced in the early universe, a relic density should still be present and...
We present the results of a preliminary study of a correction method applied to the Imaging Air Cherenkov Telescope images affected by clouds. The studied data are the Monte Carlo simulations made with CORSIKA, imitating the very high energy events registered by the Large-Sized Telescopes, a type of the telescope within the future Cherenkov Telescope Array. We implement the cloud correction...
Despite numerous studies, the origin of gamma-ray emission of blazars, Active Galactic Nuclei (AGN) with a jet aligned closely to the line of sight, is still debated. In particular, it is not entirely clear whether the gamma-ray emission is produced by leptonic or hadronic processes. In this study, we are testing the leptonic scenario for the Flat Spectrum Radio Quasar (FSRQ) 3C 279, assuming...
We have performed a detailed analysis of the X-ray spectra of the blazar Mkn 421
using Swift-XRT observations taken between 2005 and 2020, to quantify the correla-
tions between spectral parameters for different models. In an earlier work, it has been
shown that such spectral parameter correlations obtained from a single short flare
of duration ∼ 5-days of Mkn 421, can be used to...
We simulated hadronic showers at PeV-EeV energy with CORSIKA to study the massive quark production and decay modes. In this regard, we specifically studied charm meson production and their decay channels with SYBILL and QGSJet models. This understanding would possibly help implement bottom quark production and their decay in these models. The massive quark decays contribute to the atmospheric...
Star-forming galaxies (SFGs) are unique gamma-ray emitters. The observation of a correlation between their non-thermal luminosity and their star-formation rate (SFR) strongly suggests that these gamma rays result from interactions of cosmic rays injected by phenomena connected with the SFR, such as supernova remnants and massive star winds.
We aim to investigate the effect of gamma-ray...
Dark matter in cosmic structures is expected to produce signals that originate from its particle-like nature, among which the electromagnetic emission represents a relevant opportunity. However, this emission is very faint and contribute only to the unresolved background radiation. This background emission is isotropic at first order, but exhibits a degree of anisotropy since it originates...
The recently identified source class of pulsar halos may be populated and bright enough at TeV energies to constitute a large fraction of the sources that will be observed with the Cherenkov Telescope Array (CTA), especially in the context of the planned Galactic Plane Survey (GPS). In this study, we examine the prospects offered by CTA for the detection and characterization of such objects....
Observations at very large zenith angles (VLZA) can push the sensitivity of IACTs towards higher energies. There are successful examples of VLZA observations presented by MAGIC and VERITAS. Besides covering the broader energy range, the operation of Cherenkov telescopes under VLZA could increase the exposure duty cycle for observing the transient events. The updated scientific strategy of...
We applied a blind search for spatial photon clusters at energies higher than 6 and 10 GeV to sky maps of Fermi-LAT events collected in the first 12 years of operation.
We used the Minimum Spanning Tree and DBSCAN algorithms, which provided fully consistent results, detecting 13 clusters above 10 GeV. Six clusters have coordinates corresponding to known SNRs within a few arcminutes, in a very...
Fermi bubbles are giant gamma-ray structure toward the Galactic center (GC) with symmetrical north-south extension perpendicular to the galactic plane. Such giant structures toward the GC are also observed in various wavelengths from radio to X-rays, such as WMAP haze, North Polar Spur (NPS), and most recently, eROSITA bubbles. We investigated the detailed plasma condition of the NPS/Loop I...
Particle pre-acceleration constitutes a central unresolved problem in the theory of diffusive shock acceleration (DSA). This process acting at merger shocks in galaxy clusters is thought to produce relativistic electrons forming the so-called radio relics through their radio and X-ray emissions. DSA may also be a source of high- and ultra-high-energy cosmic rays and associated gamma-rays and...
The Cherenkov Telescope Array (CTA) is the future observatory for ground-based imaging atmospheric Cherenkov telescopes. Each telescope will provide a snapshot of gamma-ray induced particle showers by capturing the induced Cherenkov emission at ground level. The simulation of such events provides camera images that can be used as training data for convolutional neural networks (CNNs) to...
Blazars emit across all electromagnetic wavelengths. While the so-called one-zone model has described well both quiescent and flaring states, it cannot explain the radio emission and fails in more complex data sets, such as AP Librae. In order to self-consistently describe the entire electromagnetic spectrum emitted by the jet, extended radiation models are necessary. Notably, kinetic...
Over the past few years the IceCube observatory has detected dozens of high-energy neutrinos in association with known blazar AGN. This emission is often explained by interactions of PeV cosmic rays with thermal or atomic photon fields surrounding the jet, leading to pion production and subsequent neutrino emission. As I will argue in this talk, the multi-wavelength emission from these...
Recently the Galactic and Extra-galactic All-sky Murchison Widefield Array survey has published 27 new candidate radio supernova remnants (SNRs) which are located within the longitude ranges of 345° < l < 60° and 180° < l < 240°. To search for the gamma-ray counterparts of these candidate radio SNRs, we analyzed 14 years of Fermi-LAT data in the energy range of 0.2 - 300 GeV. There are three...
Hadronic Supercriticality (HSC) is a property of hadronic systems according to which relativistic protons lose the energy stored in them abruptly and very efficiently through the emission of violent photon outbursts. We investigate for the first time HSC in the context of an expanding system and show its direct analogy to GRB phenomenology. We simulate a variable GRB engine that injects a...
The origins of the GeV gamma-rays from nearby radio galaxies are unknown. Hadronic emission from magnetically arrested disks (MADs) around central black holes (BHs) is proposed as a possible scenario. Particles are accelerated in the MAD by magnetic reconnection and stochastic turbulence acceleration. We investigate the feature of the radio galaxies that can be explained by the MAD model. We...
We study the interaction between pulsar and stellar winds in gamma-ray emitting binaries in the presence of an inhomogeneous stellar wind. In such systems, the acceleration of particles likely occurs at the region of collision between the two winds, which is typically assumed to be smooth. However, the early-type stars that are thought to be present in some gamma-ray binaries, appear to have...
Both observational evidence as well as theoretical considerations from MHD simulations of jets suggest that the relativistic jets of active galactic nuclei (AGN) are radially stratified, with a fast inner spine surrounded by a slower-moving outer sheath. The resulting relativistic shear layers are a prime candidate for the site of relativistic particle acceleration in the jets of AGN and gamma...
GLIMPSE-C01 is a globular cluster located in the direction of Aquila (Kobulnicky et al 2005). More than a decade ago, we proposed it as a gamma ray emitter given its coincidence with the 9.6 arcmin 95% confidence error radius of the Fermi source 0FGL J1848.6-0138 (Luque-Escamilla et al 2009). The recent update of the Fermi catalogue confirms the gamma-ray detection, being now named as 4FGL...
The low-luminosity Active Galactic Nuclei M87, archetype of Fanaroff-Riley I radio-galaxies, was observed in a historically quiet state in 2017. While one-zone leptonic jet models cannot explain the radio-to-gamma-ray spectrum, we explore a hybrid jet-disc scenario. In this work, we model the overall spectral energy distribution of M87's core with a dominating one-zone lepto-hadronic jet...
Gamma-Ray Bursts (GRBs) are intense and short flashes of gamma rays followed by a long lasting multiwavelength afterglow emission, detected along the whole electromagnetic spectrum. Recently Very High Energy (VHE) emision (>100 GeV) has been obtained during the afterglow of a couple of GRBs. In this preliminary work we numerically investigate the production of VHE photons in GRB...
The very-high-energy gamma-ray emission observed from a number of Supernova remnants (SNRs) indicates particle acceleration to high energies at the shock of the remnants and a potentially significant contribution to Galactic cosmic rays. It is extremely difficult to determine whether protons (through hadronic interactions and subsequent pion decay) or electrons (through inverse Compton...
The Centre of the Milky Way galaxy (GCR), approximately 8 kpc from the Earth, is a peculiar region due to its high density of stars, the resulting amount of stellar activity, and the existence of a Supermassive Black Hole among other reasons. The acceleration and transport of Cosmic rays (CR) in such a region is naturally a subject of high interest.
Gamma-ray observations and H3+ column...
Magnetic fields are observed in various length scales from the planetary scale to the scale of galactic clusters. A certain level of the magnetic field is implied even in the voids of large-scale structures by gamma-ray observations. However, the origin of magnetic fields has not been revealed yet. Here, we propose a new generation mechanism of magnetic fields where the Biermann battery effect...
Axions are hypothetical pseudo Nabu-Goldstone bosons which arise from
spontaneous symmetry breaking in the Peccei Quinn Symmetry, which in turn is a
solution to the strong CP problem. Axions and Axion Like Particles (ALPs) are Dark
Matter candidates considring their weak gravitational interactions and weak
coupling with the Standard Model. By virtue of this coupling, theory predicts...
Blazars exhibit stochastic flux variability across the electromagnetic spectrum, often exhibiting heavy-tailed flux distributions, commonly modeled as lognormal. However, the high-energy gamma-ray flux distributions of several of the brightest flaring Fermi-LAT flat spectrum radio quasars (FSRQs) are well modeled by an even heavier-tailed distribution, the inverse gamma distribution. We...
Gamma-ray emission in the GeV and TeV energy regime has been detected towards the old supernova remnant (SNR) W28. This object is a prime candidate for the study of cosmic-ray acceleration and diffusion, as the adjacent molecular clouds provide target material for gamma-ray production and, due to its age, most particles have already escaped the shock front into the interstellar medium. While...
Radio loud Active galactic nuclei (AGN) emit synchrotron emission over a wide region of the electromagnetic spectrum. In these types of AGN the synchrotron emission is predominantly produced by non-thermal electrons in a relativistic jet. In order to study how the observed large scale radio morphology of these jets relates to the jet's their physical properties, fluid dynamic simulations can...
The electromagnetic radiation that followed the neutron star merger event GW170817 revealed that gamma-ray burst afterglows from jets misaligned with our line of sight exhibit a light curve with slowly rising flux. The slope of the rising light curve depends sensitively on the angle of the observer with respect to the jet axis, which is likely to be perpendicular to the merger plane of the...
H 1426+428 is a, so called, extreme high-frequency-peaked BL Lac object (extreme HBL) located at a redshift of z = 0.129 that was detected on a number of occasions by the previous generation of ground-based gamma-ray telescopes (Whipple, CAT and HEGRA), with its VHE flux ranging up to 80% of the Crab Nebula (Crab Units, CU) above a few hundred GeV. Current-generation TeV observatories...
The blazar OJ 287 has been proposed as a binary black hole system based on its periodic optical outburst. Black hole binary systems are scarce among blazars with parsec scale jets, and hence this source is exciting to study. The BL Lac OJ 287 is an interesting object for multiwavelength study due to its periodic outbursts. We analyzed the optical, X-ray, and γ-ray data of OJ 287 for the period...
Gamma-Ray Bursts (GRBs) are among the most energetic transients in the universe. Although mostly observed in keV to MeV energies, some GRBs have been detected in MeV to GeV energies by the Fermi-LAT. Generally, those bursts are among the brightest events of the observed population.
Motivated by this, we investigate lepto-hadronic multi-wavelength models for energetic GRBs with...
Gamma-ray binaries are a small subclass of high mass binaries where the SED peaks at energies greater than 1 MeV. For most systems the orbital parameters must be derived from radial velocity measurements of the optical companion. The gamma-ray binary HESS J0632+057 has two proposed but incompatible orbital solutions. In order to choose between the two solutions, new observations over multiple...
We present an X-ray spectro-temporal analysis of simultaneous NuSTAR and NICER observations of 4U 0114+65, to characterize the nature of the source. Light curves were obtained from the source in the range 3 - 79 keV. Two types of flares were identified in the light curve of the source, "large and small flare". A pulsation of 9275 ± 2 s obtained from the analysis of the light curves was...
The Cherenkov Telescope Array (CTA) Observatory will be the next generation ground-based very-high-energy gamma-ray observatory, sensitive from 20 GeV up to 300 TeV. The Large-Sized Telescope prototype (LST-1), currently in the commissioning phase, was inaugurated in October 2018 on La Palma (Spain). It is the first of four LST telescopes for CTA, to be built on La Palma. In 2021, LST-1...
Supernova remnants (SNRs) are thought to be the most plausible sources of Galactic cosmic rays. One of the principal questions is whether they are accelerating particles up to the maximum energy of Galactic cosmic rays (∼PeV). In this work, a systematic study of gamma-ray-emitting SNRs is conducted. Our purpose is to measure the evolution of maximum particle energies with the current best...
Relativistic shocks propagating in perfectly conductive plasmas have been extensively studied due to their central role in high energy astrophysical phenomena, with Gamma-Ray Bursts being the most prominent example. In the present work we investigate the mechanism by which a relativistic shock interacts with the propagation medium’s electromagnetic field. We assume the propagation of a shock...
A significant fraction of all γ-ray sources detected by the Large Area Telescope aboard the Fermi satellite still lacks a low-energy counterpart. In addition, there is still a large population of γ-ray sources with associated low-energy counterparts that lack firm classifications. Therefore, in the last ten years, we have undertaken an optical spectroscopic campaign to address the problem of...
Highly accurate photometry of the optical companion in gamma-ray binary systems
has the potential to enable the exploration of previously unknown phenomena. Here we report the discovery of repeated optical flares evolving on time scales of about one day in the optical light curve of the well known system LSI +61303. Their amplitude does not exceed 0.01-0.02 magnitudes and, therefore, they...
I will highlight a recent, very interesting observation (https://arxiv.org/abs/1903.10533) of gamma-ray signatures in the Circumgalactic medium (CGM) of Andromeda (M31) galaxy (~100 kpc) in the light of hadronic interaction of cosmic ray (CR) protons with the cold protons of CGM. We used two fluids (thermal + Cosmic ray) hydrodynamical simulation code PLUTO in order to simulate this scenario....
LHAASO has detected gamma-ray emission from the Crab Nebula up to PeV energies. We show here that our recent model for electron acceleration at pulsar wind termination shocks can fit well both the inverse Compton and the synchrotron emission from the Nebula. Integrating individual particle trajectories in a model of the magnetic field and flow pattern near the shock, we find that drift motion...
It was claimed that relativistic shocks propagating to uniform media cannot accelerate particles efficiently because the shocks are perpendicular shocks. However, in reality the upstream plasma has a finite density fluctuation. The interaction between the upstream density fluctuation and the shock front generates turbulence in the downstream region, so that the downstream magnetic field is...
Wind-wind collision of massive binaries produces strong shock fronts of compressed and heated plasma, with amplified magnetic fields, where particles may be accelerated to very high energies. Here we present examples of full three-dimensional magnetohydrodynamical simulations of colliding winds, which computational code also provide kinematics of passive charged particles subject to ambient...
The energy content and dissipation mechanisms leading to the observed spectra and variability properties in AGN jets are still debated. Magnetic reconnection (MR) is the most promising dissipation mechanism to account for acceleration of particles with a non-thermal energy distribution in magnetized jets. Kinetic simulations have shown how the resulting particle distribution depends on the...
Blazars are the most energetic subclass of active galactic nuclei (AGN) with relativistic jets pointing towards the observer. It is believed that jets are launched as cold non-relativistic Poynting-flux dominated outflows which accelerate to relativistic speeds at the expense of the available magnetic energy. Part of this energy is also thought to be converted into energy of non-thermal...
Investigation of astrophysical shocks has major importance in understanding physics of the cosmic rays acceleration. Electrons to be accelerated at shocks must have a suprathermal energy, which implies that they should undergo some pre-acceleration mechanism. Many numerical studies examined possible injection mechanisms, however, most of them considered homogenous upstream medium, which is an...
1ES1741+196 is one of the luminous sources that have been observed in the multi-wavelengths with the archived highest energy events observed by Magic at 80 GeV to 3 TeV within the time period 10 April 2010 until 26 May 2011. Meanwhile, the Tibet AS+MD array has observed diffuse gamma rays with energy 338 TeV-1000 TeV. These are the highest energy gamma rays that have been observed to date. We...
We study the spectrum of the energy density of gravitational waves produced during the preheating phase, at the end of inflation inhomogeneities of the time-dependent field act as a source of gravitational, and the spectrum of GWs can be linked directly to the duration of preheating. Moreover, the amplification of field fluctuations during the preheating process can lead to the amplification...
Classification of sources is one of the most important tasks in astronomy and astrophysics. About one third of sources in Fermi LAT catalogs are unclassified due to absence of plausible associations. We determine probabilistic classification of unassociated sources in 3FGL and 4FGL catalogs using machine learning methods trained on associated sources. We argue that probabilistic classification...
As an observer from within the Milky Way, it is difficult to determine its global structure. Despite extensive observational data from surveys at different wavelengths, there is no coherent picture of the structure of our own Galaxy. On the contrary, depending on the observational method, the results can differ notably. One example is the position of the Sun, with recent results ranging from 0...
The multiwavelength observation of GRB 190114C, one of the extremely bright gamma-ray bursts (GRBs), opens a new window for studying the emission mechanism of GRBs. The Very-High-Energy (VHE; >100 GeV) detection by MAGIC suggested the inverse Compton process as the emission mechanism for the VHE gamma-rays during the early afterglow phase of the burst. However, other VHE GRB detections have...
The North Polar Spur (NPS) is a giant structure that is clearly observed in both radio and X-ray all-sky maps. Although half a century has passed since its discovery, two competing ideas are still being actively debated to postulate its origin: one considers a local super-bubble near the solar system,and the other is based on a remnant of AGN and/or starburst outflow from the Galactic Center...
M31 and M33 are the closest spiral galaxies and the largest members (together with the Milky Way) of the Local group, which makes them interesting targets for indirect dark matter searches. In this paper we present studies of the expected sensitivity of the Cherenkov Telescope Array (CTA) to an annihilation signal from weakly interacting massive particles from M31 and M33. We show that a 100 h...
We analyzed the TeV gamma-ray image of a supernova remnant RX J1713.7-3946 (RX J1713) through a comparison with the interstellar medium (ISM) and nonthermal X-rays. The gamma-ray data sets at two energy bands of >2 TeV and >250-300 GeV were obtained with H.E.S.S. and utilized in the analysis. We employed a new methodology, which assumes that the gamma-ray counts can be expressed as a linear...
The Cherenkov Telescope Array (CTA) is a future ground-based observatory for gamma-ray astronomy providing unparalleled sensitivity in the energy range from $20\,$GeV up to $300\,$TeV. CTA will consist of telescopes with three different sizes. The Medium-Sized Telescopes (MSTs) will have $12\,$m reflectors with a tessellated mirror design of $86$ mirror facets each. Each mirror facet is...
We present a prototype code which implements a new way to model relativistic Cosmic Ray transport. It is based on a numerical solution to the Vlasov-Fokker-Planck equation in conjunction with a spherical harmonic expansion of the single particle distribution function. It allows for the computation of the anisotropies in the distribution of Cosmic Rays up to very high accuracy. Such effects...
Axion-like particles (ALPs) are light, pseudoscalar particles that are a beyond-the-standard-model generalization of the axion. Consequently, they are expected to couple to photons in external magnetic fields to compensate for spin difference. This coupling would induce modifications to the gamma-ray spectra of astrophysical sources, such as blazars, via ALP-photon oscillations in external...
All known small Solar System bodies have a diameter between a few km and a few thousands of km. Based on the collisional evolution of Solar System bodies, Davis et al. proposed in 2002 a model predicting the existence of a larger number of asteroids with diameters down to 10 m. In this work we propose an extension of this model to diameters of a few cm. Like all Solar System bodies, asteroids...
Gamma-ray binaries are systems composed of a massive O or Be-type star and a compact object that emit gamma-rays up to multi-TeV energies. Currently, only 9 of such systems are known, and those containing O-type stars are runaways. Because some properties of these systems are not fully understood, the discovery of new gamma-ray binaries may help to answer many open questions, and eventually...
This work investigates a new methodology to search for periods in light-curves of high-energy gamma-ray sources such as Active Galactic Nuclei (AGNs). High-energy light curves have significant stochastic components, making period detection somewhat challenging. In our model, periodic terms, drifts of the light-curves and random walk with correlation between flux points due to red noise are...
In 2015 gravitational wave event GW150914 was detected by the advanced Laser Interferometer Gravitational-wave Observatory (aLIGO), with a possible weak transient electromagnetic counterpart GW150914-GBM detected by the Fermi Gamma-ray Burst Monitor (GBM) 0.4s after the detection of the gravitational wave signal. No other such detections have occurred since (specifically with respect to BH-BH...
Previously, the non-thermal emission from galaxies has only been modelled with parametrised 1D or 2D models, which is insufficient to explain a multitude of new, spatially resolved multi-messenger data of cosmic ray (CR) spectra, at gamma-rays and in the radio. Instead, we perform high-resolution magneto-hydrodynamic (MHD) simulations of galaxies using the moving mesh code AREPO with...
At optical wavelengths, the emission from blazars is a superposition of both unpolarised thermal emission, arising from the accretion disc, broad-line region, dusty torus and host galaxy itself, and the polarised non-thermal synchrotron radiation from the relativistic electrons moving in the jet. Measuring the degree of polarisation at optical wavelengths can be used to disentangle the...
Long term periodicity in gamma-ray Blazar light curves could be linked to the innermost zone of the complex structure of AGN, like possible presence of binary system of supermassive black holes, or it could shed light on the origin of gamma-rays emission.
The work analyses around 1500 sources, whose 12 years light curves come from the Fermi LAT Repository...
Promising regions within the Galactic plane may offer more insight on the transition from younger to older pulsar wind nebulae (PWNe) evolution, as the observed very-high-energy emission provide constrains on their morphology and physical mechanisms at play. In particular, we focus on the 312° galactic longitude field of two degrees containing five powerful pulsars. Their rotational energies...
We study the effect of a tangled sub-fG level intergalactic magnetic field (IGMF) on the electrostatic instability of a blazar-induced pair beam. Sufficiently strong IGMF may significantly deflect the TeV pair beams, which would reduce the flux of secondary cascade emission below the observational limits. A similar flux reduction may result from the electrostatic beam–plasma instability, which...
The synchrotron X-ray "stripes" discovered in Tycho's supernova remnant (SNR) by Eriksen et al. (2011) is an intriguing structure in which protons might be accelerated up to PeV. However, its origin is still open. In this talk, we will explain an analysis of Chandra data taken in 2003, 2007, 2009, and 2015 of the stripes in the southwestern region of the SNR (Okuno, Matsuda, et al., 2020;...
Blazar flares are perfect phenomena to probe the extreme physics of relativistic outflows. The key method for this task is physical modeling of the variable non-thermal emission from blazar jets. Most of the numerical codes developed for blazar flare modeling, are based on the kinetic approach and solve the kinetic equation governing the evolution of the particle spectrum, as well as compute...
The extragalactic background light (EBL) is the aggregate of all optical and infrared emissions from thermal processes since the cosmic dark ages. While the integrated light of galaxies is expected to be the main contribution to the EBL, recent measurements beyond Pluto’s orbit from the New Horizon probe show a 4$\sigma$ excess in the optical band. This tension can be studied within...
Despite the enormous efforts done in very recent years, both theoretically and experimentally, the basic three questions about the CR origin remain without clear answers: what are their sources, how are they accelerated, how do they propagate?
Gamma-ray astronomy plays a fundamental role in this field. Both relativistic protons and electrons can emit in the gamma-ray band with different...
The latest Fermi/LAT catalog newly included GRS 1734-292, which is a radio-quiet Seyfert galaxy. Both star formation and jet activity of this galaxy are insufficient to explain the observed gamma-ray flux. The remaining possibility is disk wind or corona. In this talk, we report the detection of the non-thermal mm-radio emission of GRS 1734-292 using the Atacama Large Millimeter/submillimeter...
We present the Fermi-LAT light curve repository, consisting of a public library of gamma-ray light curves for variable Fermi-LAT sources on a variety of timescales. The Fermi-LAT light curve repository aims to provide publication-quality light curves on timescales of days, weeks, and months for over 1500 sources deemed variable in the 4FGL-DR2 catalog. The repository consists of light curves...
Gamma-ray observations have recently shifted the focus to higher and higher energies, with capable ground-based instruments enabling measurements in the TeV to PeV domain. While a clear prevalence of diffuse emission is observed in the GeV sky, energy-dependent cosmic-ray transport suggests a reversal of this hierarchy at higher energies. Measurements, however, are at strife regarding this...
Thermal electrons cannot directly participate in the process of diffusive acceleration at electron-ion shocks because their Larmor radii are smaller than the shock transition width: this is the well-known electron injection problem of diffusive shock acceleration. Instead, an efficient pre-acceleration process must exist that scatters electrons off of electromagnetic fluctuations on scales...
The binary neutron star merger gravitational-wave event GW170817 and observations of the subsequent electromagnetic signals at different wavelengths have helped better understand the outflows that follow these mergers. In particular, the off-axis afterglow of the jetted ejecta has allowed to probe the lateral structure of such jets, especially thanks to VLBI imagery of the source. In this...
The Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system is located on the Canary Island of La Palma and inspects the very high-energy (VHE, few tens of GeV and above) gamma-ray sky. MAGIC consists of two imaging atmospheric Cherenkov telescopes (IACTs), which capture images of the air showers originating from the absorption of gamma rays and cosmic rays by the atmosphere,...
In this contribution, we present a spectral study of extreme blazars (also eHBL) which are known to exhibit hard intrinsic X-ray/TeV spectra and extreme SED peak energies. We study four eHBLs 1ES 0120+340, RGB J0710+591, 1ES 1101-232, 1ES 1741+196 and one HBL 1ES 2322-409 using new X-ray data from AstroSat, together with quasi-simultaneous Fermi-LAT and other archival multi-frequency data....
We present the discovery of the very energetic GRB 210905A at the high redshift z=6.312 and its luminous X-ray and optical afterglow. With an isotropic gamma-ray energy of Eiso$\sim 10^{54}$ erg, GRB 210905A lies in the top 7% GRBs in the Konus-Wind Catalog in terms of energy released. *Its afterglow is also among the most luminous ever observed, and, in particular in the optical at...
The spectra of many astronomical objects, in particular GRBs, show a power law shape. Traditionally, this is commonly modeled as due to synchrotron emission from a population of accelerated particles following a power law distribution. However, here we show that multiple scattering of photons in shear layers, as expected in structured jets, naturally produces such a power law. The photons gain...
Young massive stellar clusters (YMCs) have come increasingly into the focus of discussions about the origin of PeV cosmic rays. Recently, HESS observed high-energy gamma ray emission around the YMC Westerlund 1, characterised by an energy independent, ring-like shape slightly off-set from the cluster position. We investigate the origin of this emission by modelling hadronic and leptonic...
Out of the several hundreds of gamma-ray pulsars known nowadays, only a few tens have been detected to emit also non-thermal X-ray radiation. Some aspects of the high-energy magnetospheric radiation are still unclear, such as the location of emission. In this talk I will present a radiative model which aims at explaining the high-energy emission of pulsars in an effective way, relying on only...
Interpreting observations of astrophysical shocks from radio to gamma-rays requires a detailed understanding of how shocks accelerate particles over the course of their evolution. We present a fast, multi-zone model of particle acceleration that self-consistently accounts for magnetic field amplification and shock modification due to the presence of non-thermal particles. By incorporating...
Recently, the growth of astrophysical data from science space missions, ground-based telescopes, and theoretical models, which have different services and data stores, has been exorbitant. The latter led to the necessity of unified ways of describing and accessing the data.
The Virtual Observatory (VO) is a framework for astronomical datasets, tools, and services to work seamlessly,...
Imaging Air Cherenkov Telescopes (IACTs) indirectly detect very high energetic (VHE) gamma rays. They observe the Cherenkov light emitted in electromagnetic shower cascades the gamma rays induce in the atmosphere. A precise reconstruction of a primary photon’s energy and the source flux depends heavily on accurate Monte Carlo (MC) simulations of the shower propagation and the detector...
Gamma-ray emitting narrow-line Seyfert 1 galaxies (NLS1) constitute an intriguing small population of Active Galactic Nuclei (AGN) with unexpected gamma-ray emission and debated fundamental properties, similar to low power flat-spectrum radio quasars (FSRQ). They are jetted, gamma/radio-loud Seyfert galaxies, with relatively low BH masses, accreting at exceptionally high, near-Eddington rates....
The Imaging X-Ray Polarimetry Explorer (IXPE) is an X-ray telescope capable of extracting information of the X-ray polarization of astrophysical sources in the 2-8 keV band. After a successful launch, IXPE started science operations in January 11 2022. During the first months of operations, IXPE obtained exposures of five TeV-emitting BL Lac-type blazars: Markarian 501, Markarian 421, S5...
Ground-level particle detection is a powerful approach to TeV gamma-ray astronomy. Ground-particle array observatories such as HAWC detect gamma-rays via water-Cherenkov detector units in tanks or buildings. This contribution is about the possibility of deploying water-Cherenkov detector units directly into a natural lake, specifically as one option for the future Southern Wide-field Gamma-ray...
HESS J1534-571 is a supernova remnant that has been discovered in the H.E.S.S. Galactic plane survey. While a radio counterpart has been identified, a putative X-ray counterpart of the shell has eluded detection so far. We present XMM-Newton observations that have been obtained towards the brightest part of the TeV shell, which complement earlier Suzaku observations of other regions of the...
