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,...
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...
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...
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...
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...
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...
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...
