: The extragalactic background light (EBL) contains all the radiation emitted by nuclear and accretion processes in stars and compact objects since the epoch of recombination. Measuring the EBL density directly is challenging However, gamma-ray astronomy provides an alternative approach to indirectly studying the EBL through the observation of gamma-ray absorption in the spectra of distant...
The Andes Large area PArticle detector for Cosmic ray physics and Astronomy (ALPACA) is a new air shower array experiment under construction in the Bolivian Andes at the altitude of 4740m. The aim of the experiment is to explore the southern gamma-ray sky beyond 100 TeV to reveal the yet unknown PeV cosmic-ray accelerators. The surface array consisting of 401 plastic scintillating counters...
The intrinsic gamma-ray flux from extragalactic sources in the very-high-energy (VHE; E>100GeV) regime is subject to attenuation due to interactions with photons of the extragalactic background light (EBL), leading to pair production. Consequently, the Universe is expected to appear opaque to VHE photons above certain energy thresholds, depending on the redshift of the source. An oscillation...
A collaboration of scientists across the globe is currently working on the development of the Southern Wide-field Gamma-ray Observatory (SWGO), a next-generation gamma-ray facility to be constructed in Chile. SWGO will provide wide field-of-view coverage with a high duty cycle for a large portion of the southern sky and complement observations of existing ground-based survey instruments in the...
The Southern Wide-field Gamma-ray Observatory (SWGO) is a next-generation experiment and offers precise wide-field observations of the southern gamma-ray sky. SWGO will be located in Pamba la Bola, Chile, at an altitude of 4770 m, cover an area of 1 kmยฒ and complement CTA and LHAASO. By leveraging double-layered Water Cherenkov Detectors, the SWGO design will facilitate gamma-ray observations...
The history of photon production and galaxy evolution since the epoch of reionization is encoded in the extragalactic background light (EBL). Above an energy threshold, $\gamma$-rays can interact with the optical and infrared photons that dominate the EBL, resulting in an absorption imprint in the spectra of extragalactic sources. The combined observations of the current generation of...
The SWGO collaboration proposes constructing a wide-field-of-view observatory to explore the southern hemisphere sky in the 100 GeV - 1 PeV energy range. The selected site is the Atacama Astronomical Park in Chile. Currently, the HAWC and LHAASO experiments are the only ground-based arrays for gamma-ray detection operating in this energy range, and both are located in the northern hemisphere....
The diffuse gamma-ray background (DGRB) measured by various telescopes spans over a wide energy range from keV to around TeV. In the energy range (100 MeV-820 GeV), the DGRB can be explained by sources such as blazars and star forming galaxies. Whereas in the lower energies up to around 0.3 MeV, the dominant sources are found to be active galactic nuclei and Seyfert galaxies. However, in the...
The extragalactic background light (EBL) encodes the cumulative radiation from extragalactic sources across ultraviolet to infrared wavelengths, serving as a key probe of galaxy formation and cosmic evolution. This study enhances previous EBL reconstructions by incorporating the Spectral TeV Extragalactic Catalog (STeVECat), expanding the sample from our previous study to include a larger set...
The forthcoming Southern Wide-field Gamma-ray Observatory will be located in Chile and ideally situated to observe the southern Galactic Plane. With its continuous survey capabilities and large collection area at high energies โฅ 100 TeV, SWGO will significantly contribute to studies of galactic gamma-ray sources. In this contribution, we refine the galactic science case for SWGO in light of...
The extragalactic background light (EBL) is a key observable for understanding galaxy evolution and cosmology, as it represents the cumulative radiation from all star-forming galaxies throughout cosmic history, spanning ultraviolet to far-infrared wavelengths, with an additional, less certain contribution from active galactic nuclei. High-energy gamma rays from distant blazars interact with...
The Southern Wide-field Gamma-ray Observatory (SWGO) will be a next generation ground array experiment probing the Southern sky in search of gamma-ray sources from the Galactic plane. The experiment will be located in the Atacama Astronomical Park at 4770 m above sea level. The observatory will be a wide field of view and high duty cycle (almost 100%) array measuring the Extensive Air Showers...
The ASTRI Project is an international collaborative effort led by the Italian National Institute for Astrophysics (INAF) to develop, build, and operate a facility consisting of nine four-meter class Imaging Atmospheric Cherenkov Telescopes dedicated to gamma-ray astronomy in the 1โ200 TeV range. The ASTRI Mini-Array is currently being installed in Tenerife at the Observatorio del Teide, and...
The InterGalactic Magnetic Field (IGMF) is believed to be a remnant of the Big Bang and the origin of cosmological magnetic fields. However, it has yet to be detected. The Cherenkov Telescope Array Observatory (CTAO) will have the potential to place stricter constraints on the IGMF by analysing data from AGN and GRBs. In this study, we propose to simulate realistic observations in CTAO of GRBs...
The origin of magnetic fields on cosmological scales remains one of the longstanding problems in cosmology. Magnetic fields observed in galaxies and clusters are typically explained through the amplification of weak seed fields. However, the nature of these weak seed fields remains largely unknown. Two scenarios are usually considered: the cosmological and the astrophysical scenarios.
To...
The ASTRI MiniโArray is an international project led by INAF to install and operate nine innovative Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Observatorio del Teide site e, resulting from a hosting agreement between INAF and IAC. The facility will operate for at least 8 years. It will deeply observe the Galactic and extra-galactic sky at TeV energies to study compelling open...
Intergalactic weak magnetic fields can have non-negligible effects on the electromagnetic cascades induced by blazar gamma-ray emission. Secondary electrons and positrons are produced by primary gamma rays of energies ~TeV and can be magnetically deflected out of the line of sight to the source. However, these leptons can perturb the background intergalactic medium (IGM), resulting in the...
The ASTRI Mini-Array is an international project to build and operate an array of nine 4-m diameter Imaging Atmospheric Cherenkov Telescopes (IACT) at the Observatorio del Teide (Tenerife, Spain). The array has been designed to perform deep galactic and extragalactic gamma-ray sky observations in the 1-200 TeV energy range. As of today, the first telescope ASTRI-1 is fully operative, and in...
Relativistic pair beams created in the intergalactic medium (IGM) by TeV gamma rays from blazars are expected to produce a detectable GeV-scale electromagnetic cascade, but the cascade component is absent in the spectra of many hard-spectrum TeV-emitting blazars. One common explanation is that weak intergalactic magnetic fields deflect the electron-positron pairs away from our line of sight....
The Large High Altitude Air Shower Observatory (LHAASO) has recently detected over 40 ultra-high-energy (UHE) gamma-ray sources. However, many of these sources are extended, and some are located within a small angular region (~1ยฐ) that LHAASO cannot resolve clearly. To address these limitations, the Large Array of Imaging Atmospheric Cherenkov Telescopes (LACT) has been proposed and is...
Large Array of imaging atmospheric Cherenkov Telescope (LACT) is an array of 32 Cherenkov telescopes with 6-meter diameter mirrors to be constructed at the LHAASO site, aiming to enhance our understanding of ultra-high energy gamma ray astronomy. This work presents a detailed performance assessment of the LACT array, focusing on the IRFs for both an 8-telescope subarray configuration optimized...
The Single-Mirror Small-Size Telescope (SST-1M) is an Imaging Atmospheric Cherenkov Telescope designed for detecting very high-energy gamma rays. With a compact design achieved through the adoption of silicon-photomultiplier pixels and a lightweight structure, SST-1M offers a large field of view of about 9ยฐ and features a mirror system of 4 m diameter with a PSF (at 80% of photon inclusion) of...
More than 50 high-frequency-peaked BL Lac objects (HBLs) have been detected by ground-based TeV gamma-ray observatories, making them the dominant population of extragalactic sources observed at energies above 0.1 TeV. The fluxes of HBLs are often reported only during high-flux states, biasing our understanding of the properties and duty cycle of these sources towards flares. In recent years,...
The Antarctic Demonstrator for the Advanced Particle-astrophysics Telescope (ADAPT) is a NASA suborbital mission scheduled for a high-altitude balloon flight over Antarctica during the 2025-2026 season. ADAPT aims at validating key detector technologies for the forthcoming space-based Advanced Particle-astrophysics Telescope (APT) mission, an MeV-TeV gamma-ray telescope designed to provide an...
The astrophysical community is currently focusing on the development of next-generation gamma-ray telescopes designed to detect low-energy photons in the MeV-GeV range, operating in both the Compton and pair conversion regimes. The proposed Advanced Particle-astrophysics Telescope (APT) is a planned space-based, MeV-TeV gamma-ray mission aimed at providing an order of magnitude improvement in...
Extremely high-peaked BL Lac objects (or extreme blazars) are unique extragalactic laboratories where particle acceleration processes are pushed at their physical limits. In these blazars, synchrotron emission peaking above keV energies is reprocessed to very-high-energy (VHE, energies > 100 GeV) gamma rays, often resulting in very hard TeV spectra. Over the past two decades, they have...
Gamma-Ray Bursts (GRBs) are among the most energetic events in the Universe. Despite over 50 years of research and measurements their prompt emission remains poorly understood, with key questions surrounding the structure of relativistic jets, magnetic field configurations, and dominant radiation mechanisms. Polarization measurements are critical in resolving these uncertainties. The POLAR...
Changing-look (transitional) blazars shift between subclasses at different flux states. It is, therefore, crucial to study them to comprehend the fundamental physics governing blazars and the relationships between their different subclasses. VERITAS has detected very-high-energy (VHE; E>100 GeV) emissions from several transitional blazars during flaring states, revealing their capability of...
DR-TES (Dilution Refrigerator - Transition Edge Sensors) is a balloon-borne experiment aimed at demonstrating advanced cryogenic and detector technologies for X-ray and gamma-ray spectroscopy in a near-space environment. The mission utilizes a low-temperature TES detector array, cooled to ~75 mK by a miniature dilution refrigerator (mini-DR), which itself is pre-cooled by a liquid helium...
Key sources of VHE gamma rays include extra-galactic objects such as blazars, gamma-ray bursts (GRBs), and other interesting transients phenomena. The studies on these targets provides critical insights into astrophysical phenomena, including black hole accretion, particle acceleration, and explosion dynamics. The Large High Altitude Air Shower Observatory (LHAASO), located in China, is a...
During its first phase, from 2004 up to the end of 2012, the H.E.S.S. (High Energy Stereoscopic System) experiment observed the extragalactic skies for more than 2700 hours. These data have been re-analysed in a single consistent framework, leading to the derivation of a catalog of 23 sources. In total, about 6.5% of the sky was observed, allowing for several additional studies to be...
WINK is a proof of concept prototype designed to test, enhance and approve the base technology of Crystal Eye. While Crystal Eye is intended for all-sky monitoring of X and gamma rays in the 0.1โ30 MeV range, whose primary objectives include investigating the prompt emissions of Gamma Ray Bursts (GRBs) - and acting as pointing system for other detectors in order to study the associated...
The DArk Matter Particle Explorer (DAMPE) is a spaceborne high-energy particle detector launched on December 17, 2015, as part of an international collaboration led by the Chinese Academy of Sciences. DAMPE is designed to investigate cosmic-ray electrons and ฮณ-rays with unprecedented energy resolution and sensitivity. By operating in low Earth orbit at an altitude of approximately 500 km,...
VERITAS is one of the worldโs most sensitive very-high-energy (VHE; E > 100 GeV) gamma-ray observatories. Over 8,600 hours (~50%) of its good-weather observations were targeted on active galactic nuclei (AGN). These observations include an ongoing, comprehensive program to discover new VHE AGN, target-of-opportunity responses to flaring AGN, and both monitoring and deep campaigns on known VHE...
Simultaneously with the Event Horizon Telescope (EHT) imaging the black-hole shadow of M87 for the first time in 2017, an extensive multi-wavelength (MWL) observational campaign was conducted involving ground and space-based instruments covering fifteen decades of energy ranging from radio to very high-energy gamma rays. During this first campaign, the innermost knot HST-1 and the core of M87...
The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer class space-based mission scheduled to launch in 2027. COSI will function as a wide field imager, spectrometer, and polarimeter, and it will be sensitive to photons between 0.2 - 5 MeV. The four primary science goals of COSI are 1) uncover the origin of Galactic positrons, 2) reveal Galactic element formation, 3) gain insight...
MeV gamma-ray astronomy remains relatively underexplored, despite
extensive worldwide efforts to investigate this crucial energy range.
To address this challenge, we have demonstrated the high-performance
capabilities of an electron-tracking Compton camera (ETCC) during the
Sub-MeV/MeV gamma-ray Imaging Loaded-on-balloon Experiment (SMILE)
missions. The ETCC employs a gaseous...
As the closest known active galactic nucleus, Centaurus A provides a rich environment for astrophysical exploration, being detected from radio to gamma rays. Recently, very-high-energy gamma rays have been measured by the HESS observatory. The signal is associated with the jet, revealing the presence of relativistic electrons. However, the underlying acceleration mechanism remains uncertain....
Suggestion: The radio galaxy M87 has been detected at energies above 1 TeV with a significance exceeding 5$\sigma$ using nearly 10 years of data from the HAWC observatory. To gain further insight into the nature of this emission, we model it with different physical scenarios, ranging from a simple Synchrotron Self-Compton leptonic model to hadronic models. We constrain the physical parameter...
newASTROGAM is a breakthrough mission concept for the study of the non-thermal Universe from space with gamma rays in the energy range from 100 keV to 3 GeV. It is based on an advanced space-proven detector technology, which will achieve unprecedented sensitivity, angular and energy resolution combined with polarimetric capability. Since the MeV gamma-ray energy range is the most...
The Galactic Annihilation Line Explorer (GALE) mission will address a long-outstanding question in our understanding of the sources of Galactic positrons: whether they are produced by unresolved astrophysical sources or created via diffuse processes, possibly due to dark matter decay and/or annihilation. The problem of Galactic positrons that produce 511-keV gamma-ray emission from the...
Very high energy (>200 GeV) gamma-ray emission was discovered from the blazar 1ES 1028+511 located at redshift z= 0.361 as part of the VERITAS AGN Discovery Program. It is classified as an extreme high-frequency-peaked BL Lac object (EHBL) and is potentially an interesting object for multi-messenger studies. This EHBL was selected for observation because of its bright X-ray emission and its...
The well-known blazars, Markarian 421 (Mrk 421) has been detected with high significance by LHAASO. Since the observation of gamma radiation from blazars provides insights into the physical processes occurring in their relativistic jets making it crucial to study their broad-band spectral energy distribution (SED). For this purpose, contemporaneous data in the gamma-ray band along with X-ray...
MeV gamma-ray observations are important to deepen our understanding of the physics of high energy phenomena such as active galactic nuclei and gamma-ray bursts. Particularly an all-sky MeV gamma-ray facility with a good localization accuracy of about 1 degree can significantly increase the number of follow-up observations of transient events, increasing opportunities for multi-messenger...
The Compton Spectrometer and Imager (COSI), scheduled for launch in 2027, will improve sensitivity for MeV gamma-ray line observations by an order of magnitude, opening new windows to study cosmic nucleosynthesis. Primary targets include the 511 keV emission from positron annihilation, $^{26}$Al from stellar nucleosynthesis, and $^{44}$Ti from supernova remnants. With its wide field of view,...
Blazars are highly variable sources and show variability down to minute time scales. The current generation of Imaging Atmospheric Cherenkov Telescopes like MAGIC are able to probe the spectra of the brightest blazars at short time scales, especially in their flaring states. In this work, we characterize the variability and daily Spectral Energy Distribution (SED) evolution of the archetypal...
Ultra-High-Energy (UHE, E >100 TeV) gamma rays are one of the few channels to search for and study galactic PeVatrons. Among the most promising PeVatron candidates are the many UHE gamma-ray sources that have recently been identified on the Galactic Plane. Ground-based particle detectors see these sources as extended rather than point-like, and current generation Imaging Atmospheric Cherenkov...
The High-Altitude Water Cherenkov (HAWC) observatory, located in Volcรกn Sierra Negra, Mรฉxico, is designed to detect very high-energy (VHE) gamma rays and has provided continuous sky observations in the range of hundreds of GeV to hundreds of TeV since it began operations in 2015. Over nine years (2015โ2024), HAWC has revealed the evolution of the light curve of the blazar Markarian 421 (Mrk...
The ALPACA experiment is a new project in Bolivia designed to observe cosmic rays and gamma rays in the TeVโPeV energy range. It consists of a large air-shower array (83,000 mยฒ) and a water-Cherenkov-type muon detector (3,600 mยฒ) and aims to survey PeVatron candidates in the southern sky, including the Galactic Center. The surface detectors of the prototype array, ALPAQUITA, has been fully...
Markarian 421 (Mrk 421) is one of the closest and brightest high-frequency peaked blazars, located at a redshift of z = 0.031. It is a strong source of gamma rays, and its broadband emission has been extensively studied over the years through multi-wavelength observations from various telescopes.
Mrk 421 has been a target of observational campaigns conducted by the SST-1M telescopes โ two...
The upcoming Cherenkov Telescope Array Observatory (CTAO) represents the next generation of Imaging Atmospheric Cherenkov Telescopes (IACTs), offering a significantly enhanced sensitivity, up to five to ten times greater than existing instruments. Its first prototype, the Large-Sized Telescope (LST-1), is currently operational at the Roque de los Muchachos Observatory in La Palma, Spain. Deep...
In this talk, I will present the first study of an outburst from a high synchrotron peaked blazar (HSP) with X-ray polarimetry and very high-energy (VHE; E >0.1 TeV) gamma ray measurements. While the mechanisms driving flares in blazar jets remain poorly understood, the associated spectral variations imply that particle (re)acceleration must play a central role. For HSPs, the advent of...
SST-1M is a prototype single-mirror Small-Sized Cherenkov Telescope
designed for very-high-energy (VHE) gamma-ray astronomy. With a 4
meter primary mirror and a 5.6 meter focal length, it provides a wide 9-degree field of view, optimized for detecting VHE gamma-rays from 1 TeV
to several hundred TeV. Its focal plane is equipped with DigiCam, a fully
digital trigger and readout camera made...
I will show that current mm-to-X-ray polarization trends observed during recent IXPE campaigns for high-synchrotron peaked blazars and the ROBOPOL trend for Fermi blazars, which relate the fractional polarization to the peak frequency of the synchrotron emission, can be successfully reproduced by a multi-zone scenario without the need for an energy-stratified scenario. I will also discuss some...
With a large field-of-view and almost full duty cycle, LHAASO-WCDA is appropriate to monitor the VHE emission from extra-galactic transient sources like GRBs and AGNs, or galactic variable sources like binaries, pulsars and nova. However, these sources either suffer from severe EBL absorption at high energies or have an energy spectral cutoff at sub-TeV range, making them faint or even...
The Large Area Telescope onboard the Fermi Gamma-ray Space Telescope (Fermi-LAT) has surveyed the sub-GeV/GeV gamma-ray sky and achieved high statistics measurements since 2008. However, observation at low galactic latitudes remains difficult owing to the lack of the angular resolution, and new issues following the operation of Fermi-LAT have arisen.
We devised a precise gamma-ray observation...
The GRAINE project observes cosmic gamma-rays, using a balloon-borne emulsion-film-based telescope in 10MeV-100GeV energy band. The high spatial resolution (<1ฮผm) of the emulsion films makes high angular resolution (5โฆ at 100 MeV and 0.8โฆ at 1 GeV) and polarization sensitivity for the gamma-ray. One of our target is Galactic center region. A few GeV Gamma-rays are expected to be produced via...
We are advancing precise observations of cosmic gamma rays in the sub-GeV/GeV energy range using a large-scale nuclear emulsion telescope with high angular resolution (0.1ยฐ at 1 GeV), deployed on a balloon. We conducted balloon experiments in 2011, 2015, 2018, and 2023. In 2018, we achieved the first detection of an astronomical gamma-ray source and imaged the Vela pulsar with the worldสผs...
The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a mission concept developed by a large European collaboration under study by ESA since2018 and currently one of the three candidatesย M7 mission for a launch in the late '30s. THESEUS aims to fully exploit Gamma-Ray Bursts for investigating the early Universe and as key phenomena for multi-messenger astrophysics. By...
The Cosmic X-ray Background (CXB) traces the integrated energy released by black hole accretion across cosmic history, primarily from Active Galactic Nuclei (AGN). The Cosmic X-ray Background Explorer (CXBe) aims to measure the CXB spectrum with unprecedented ~1% accuracy, an order of magnitude improvement over the current ~15-20% uncertainties. This advancement will refine synthesis models...
The CUbesat Solar Polarimeter (CUSP) project is a CubeSat mission planned for a launch in low-Eart orbit and aimed to measure the linear polarization of solar flares in the hard X-ray band by means of a Compton scattering polarimeter. CUSP will allow to study the magnetic reconnection and particle acceleration in the flaring magnetic structures of our star. CUSP is a project in the framework...
Outflows from star-forming regions are thought to have a profound effect on galaxy evolution. The role of cosmic rays in such outflows is however not clear at present. We report on the discovery of a cosmic-ray loaded outflow from the young massive star cluster Westerlund 1, which is known to accelerate cosmic rays to several tens of TeV. The outflow manifests itself as a ~150 pc-diameter GeV...
Stellar wind termination shocks are considered potential sites for efficient particle acceleration, allowing an explanation for the overabundance of Neยฒยฒ observed in cosmic rays (CRs) through Wolf-Rayet stars (WRs) and providing a minor but necessary contribution to the observed flux of Galactic CRs. However, only a few powerful star clusters such as Westerlund 1 and Cygnus OB2 have been...
Young massive star clusters (YMSCs) can produce gamma rays in the very-high-energy (VHE, E>100 GeV) range and have been proposed as sources that can accelerate cosmic rays up to PeV energies. Observations with current instruments have lead to the detection of only a few YMSCs but future instruments should significantly increase this number. However, the details of the production of the VHE...
Cosmic-ray acceleration up to PeV energies has been suggested to take place in massive and young stellar clusters. The formation of a strong termination shock driven by the collective action of stellar winds in compact clusters offers a promising location where efficient particle acceleration might take place over Million year timescales. Moreover, the impulsive acceleration from supernova...
Massive Star Clusters (SCs) have been proposed as important CR sources, with the potential of explaining the high-energy end of the Galactic cosmic-ray (CR) spectrum, that Supernova Remnants (SNRs) seem unable to account for. Thanks to fast mass losses due to the collective stellar winds, the environment around SCs is potentially suitable for particle acceleration up to PeV energies and the...
Recent Fermi LAT observations of nearby giant molecular clouds show deficits in the gamma-ray residual map when the expected diffuse emission is modelled assuming uniformly distributed cosmic rays (CRs) [1]. The authors pointed out that the observed emission โholesโ reflect the lack of penetration of <โผ10 GeV CRs into denser regions, and proposed that the CR deficit is caused by slower CR...
Spinning super-massive black holes at the center of galaxies can launch powerful magnetized jets. When these jets are oriented within a few degrees of our line of sight, they are called blazars, active galactic nuclei that exhibit variable, non-thermal emission across the entire electromagnetic spectrum, from radio waves to gamma rays. 3C 279 is an archetypal blazar with a prominent radio jet...
Despite IC 443 being among the most studied Galactic supernova remnants (SNRs) across the entire electromagnetic spectrum, the complex region around it has yet to be clarified. A detailed analysis of IC 443 surroundings yielded the detection of extended GeV gamma-ray emission spatially coincident with the G189.6+3.3 SNR. Despite the lack of a complete radio continuum image, the position and...
G032.8-00.1 (or Kes 78) and G032.4+00.1 are two adjacent (in projection) supernova remnants (SNRs), apart by 0.4 deg. Both remnants have been investigated in the radio and X-ray bands. Both were previously considered to be related with the 2FGL J1850.7-0014c gamma-ray source. However, such an association was abandoned in the latest Fermi-LAT catalogs. The current view supports the detection...
PG 1553+113 is a distant TeV blazar known for its ~2.2-year periodic gamma-ray signal detected by Fermi. We present results from a decade-long, multiwavelength monitoring campaign of this source.
Our analysis confirms the periodicity in gamma-ray and optical bands; however, no significant periodicity is found at TeV and X-ray energies, based on observations with MAGIC and Swift-XRT,...
An extended Very-High-Energy (VHE) gamma-ray source coincident with the location of the large radio shell-type SNR G108.2-0.6 is newly discovered by LHAASO. With no excess gamma-ray emission above 100 TeV, the source energy spectrum is well fitted by a power-law function, implying no obvious cutoff. The VHE gamma-ray observation of this extended source has revealed a large shell-type structure...
We present the results of more than 15 years of Fermi Large Area Telescope (LAT) monitor observations of the high-energy peaked BL Lac object PG 1553+113 at E>100 MeV and E>1 GeV gamma-ray bands, in comparison with optical, radio and X-ray multifrequency monitoring data. A long-lived, 2.1-year periodic modulation, of the gamma-ray flux is continuing to be significant at a 4 sigma level...
Supernova remnants (SNRs) are known to accelerate particles up to relativistic energies. We have recently discovered a new SNR, G310.7-5.4 at high Galactic latitude using the ASKAPโs EMU and POSSUM surveys at 943.5 MHz (Burger-Scheidlin et al., in prep.). The faint, extended object has an apparent size of 30.6โฒ ร 30.6โฒ and shows the typical SNR bilateral shell structure. Strong linear...
The blazar 1ES 1959+650 is one of the nearest TeV extragalactic sources to us. Its gamma-ray spectrum is very hard, with a spectral index of only around 1.9 in the GeV energy band reported in 3FHL (the 3rd Fermi-LAT high energy sources catalog). Years ago, a TeV orphan flare was discovered in this source, and it was considered a potential neutrino source. Shortly after the real-time transient...
Over the past millennium, only five Galactic supernovae have been observed and recorded by contemporary astronomers, and their current-day counterparts subsequently identified. The remnants of four of these have all been very deeply studied, and ultimately detected, by TeV instruments after exposures of typically hundreds of hours. The measured TeV fluxes range from 1 Crab (by definition) down...
Long-term and unbiased monitoring of rapidly variable gamma-ray sources, such as active galactic nuclei (AGNs), is essential for elucidating the emission mechanisms behind these extragalactic objects. The Large High Altitude Air Shower Observatory (LHAASO), one of the largest ground-based experiments, provides valuable insights into very high energy (VHE) phenomena, enabling comprehensive...
Supernova remnants are known to accelerate particles to relativistic energies on account of their non-thermal emission. Fast variability in the non-thermal synchrotron emission has been detected in multiple remnants and was linked to local properties of the magnetic fields. Further, variations in the long-term radio and x-ray flux have been reported for various objects as well.
RCW86 is one...
The intermediate synchrotron-peaked BL Lac B2 1811+31 (z=0.117) underwent a period of high activity from the optical band to very-high-energy (VHE; 100 GeV < E < 100 TeV) gamma rays in 2020. Following a high-state detection by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope in the high-energy gamma-ray band (HE; 100 MeV < E < 100 GeV), a dedicated multi-wavelength...
Blazars are among the most powerful gamma-ray emitters, displaying rapid variability and extreme spectral properties. In this study, we systematically search for the most extreme high-energy blazars using 12 years of Fermi Large Area Telescope data, aiming to identify instances of spectral hardening in their gamma-ray spectra. This phenomenon is characterized by a flux that decreases with...
The Vela SNR region is a bright, nearby and complex region of non-thermal emission which at its centre it contains a powerful pulsar and its associated pulsar wind nebula, commonly known as Vela X. Due to its nature as one of the most local cosmic ray accelerators it has been an object of interest for many studies at the highest energies.
We present a new detailed study of VHE gamma-ray...
Our exploration of the sky at the highest photon energies has recently benefited from a number of major advances, notably the expansion of the spectral window up to the PeV range, the probing of emissions over larger and larger angular scales, and the coverage of significant portions of the Galaxy. Such a broad view can be expected to lead to significant progress in our understanding of the...
Blazars show variability across the entire electromagnetic spectrum and over a wide range of timescales. In some cases, characteristic emission patterns have been observed, such as the multi-year modulation detected in PG 1553+113. Quasi-periodic oscillations (QPOs) can arise from various astrophysical mechanisms, including jet precession, accretion disk instabilities, and binary supermassive...
Blazars, a subclass of active galactic nuclei (AGN), are known as the strong emission and frequent activities. The blazar PKS 2155-304 is a high synchrotron-peaked BL Lac with redshit $z=0.116$. On 2006 July 28, an extremely remarkable outburst of VHE $\gamma$-ray emission was reported by H.E.S.S from this blazar, with an average flux more than 10 times the quasi-stable-state value. On the...
The origin of cosmic rays has been an active area of research since their discovery over a century ago. Supernova remnants (SNRs) are believed to be able to accelerate cosmic rays up to the โkneeโ of the observed cosmic-ray spectrum. Although the acceleration at SNR shocks has been extensively modelled, it is still not clear that cosmic rays are able to escape these sources. After...
In this talk, I will review our recent progress and important findings of the beaming effect and relativistic jet property in gamma-ray blazars detected by the Fermi-Large Area Telescope (Fermi-LAT). Blazars are a particular class of radio-loud Active Galactic Nucleus (AGNs), characterized by many distinctive observational properties, which are due to the relativistic beaming effect. Since the...
We present the analysis of 4 year LHAASO data of the middle-aged SNR W44 and the massive mocecular gas complex that surrounds it. We confirm the presence of the extended gamma-ray structure located near the remnant. Based on the high-resolution gas maps, we demonstrate that gamma-ray structures are caused by the interaction of escaped relativistic particles with Moclecular CloudsใWe argu that...
The Cherenkov Telescope Array Observatory (CTAO) is the next-generation ground-based observatory for gamma-ray astronomy, covering a very broad energy range from 20 GeV to beyond 100 TeV. The luminosity function (LF) of very-high-energy (VHE) blazars measures their evolution over cosmic time, constrains their contribution to unresolved radiation fields, and connects them to source populations...
CTA 1 is a composite supernova remnant featuring a shell structure and an inner Pulsar Wind Nebula. The shell is visible in the radio band, while Fermi has detected the radio-quiet pulsar PSR J0007+7303 at its core. Gamma-ray detectors such as LHAASO and VERITAS have detected TeV emission in the vicinity of the pulsar. However, the derived SEDs from LHAASO WCDA and VERITAS show significant...
Pulsar wind nebulae (PWNe) are prominent sources in the very-high energy (VHE) gamma-ray sky, constituting the most numerous identified source class in the H.E.S.S. Galactic Plane Survey (HGPS). They are comprised of energetic particles originating from the pulsar and expanding into the surrounding medium. As such, PWNe are of very high scientific interest as PeVatron candidates, objects that...
VER J0521+211 is one of the brightest BL Lac objects detected in the TeV gamma-ray regime, located at a redshift of z=0.108 and 3 deg away from Crab Nebula.It was not included in 1LHAASO catalogue, but manifests with 5.6 sigma in 978-day data from March 2021 to Jan 2024. WCDA enables continuous long term monitor, which will provide important information of the average emission of this blazar...
Superluminous supernovae (SLSNe) are a recent class of astronomical transients whose luminosities exceed those of typical core-collapse supernovae by 10 to 100 times. What makes SLSNe so different from regular core-collapse SNe is still in debate. There are mainly four different energy sources being considered to explain the high peak luminosity of SLSNe: ejecta fallback accretion onto a black...
We analyzed multiwavelength data of the BL Lac object S5 0716+714 to investigate its emission mechanisms during a flaring state observed in early 2015. We examined the temporal behavior and broadband spectral energy distributions (SEDs) during the flare. The size of the $\gamma$-ray emission region was estimated based on the variability timescale. To explore the multiwavelength properties of...
PKS 2155-304 is a well-known high-frequency peaked BL Lac (HBL) at redshift z=0.116, which has been extensively studied across the electromagnetic spectrum due to its rapid and large-amplitude variability. Several violent outbursts in X-rays and gamma rays have been observed in the past, with intra-night variability in very-high-energy gamma rays (VHE; E > 100 GeV) detected down to the minute...
The observation of PeVatrons is without doubtย one of the major breakthroughs in gamma-ray astronomy. The quest for Galactic cosmic-ray candidates goes hand-in-hand with these discoveries. However, with the advent of the very high-energy observations, many new questions arise. In many of the reported sources the origin of the particles responsible for the gamma-ray is unclear, in many cases...
NVSS J073326+51535 is an extreme high-frequency-peaked BL Lac (EHBL) object located at redshift 0.065. It was discovered at very-high-energy (VHE; E > 100 GeV) by the MAGIC collaboration in 2018. We announce the VHE detection of NVSS J073326+51535 by the VERITAS collaboration and present a multi-wavelength study of this EHBL. These recent observations aim to further constrain the emission...
The W51 giant cloud is one of the largest star-forming regions in the Galaxy. Several experiments have detected gamma-ray emissions from the W51 complex: Fermi (Jogler and Funk 2016), MAGIC (Aleksic et al. 2012), HESS (H.E.S.S. Collaboration et al. 2018), HAWC (Albert et al. 2020), and more recently, LHAASO (Cao et al. 2024). This complex contains two star-forming regions, known as W51A and...
Most modern studies of Active Galactic Nuclei (AGN) rely on broadband spectral analyses to constrain the plethora of particle acceleration and emission processes. Traditional analysis methods are often hindered by the use of proprietary tools tailored for each participating instrument, making it challenging to integrate multi-wavelength data in a consistent, reproducible[,,] and statistically...
We report the analysis results in the 2-degree range around G57.2+0.8 by LHAASO using the WCDA data and KM2A data up to July 2024. Compared with other templates, a template with one dust and three additional sources can explain the high-energy gamma-ray emission well in this region. During the processing, the location of the TeV source (TeV J1943+213) was fixed, and the other two fitted...
The "Dragonfly" Pulsar Wind Nebula and its surroundings is a complex region with several HE to UHE gamma-ray point-like and diffuse sources accompanied by their multi-wavelength counterparts. MILAGRO discovered the VHE emission in 2012, making it the second brightest MILAGRO source in the northern hemisphere. The region was later resolved into more VHE sources by VERITAS, revealing a complex...
Ultra Fast Outflows (UFOs) are sub-relativistic dense winds of wide aperture angle, launched from Active Galactic Nuclei, at which strong shocks (Mach number $\gg$ 1) are expected to form.
At these shocks, particle energisation through diffusive shock acceleration (DSA) should lead to the copious production of gamma rays and neutrinos, in the interaction of accelerated charged particles...
Supernova remnants (SNRs) have been widely believed to be the dominant source of Galactic cosmic rays, which are accelerated up to ~ $10^{15.5}$ eV through the process called Fermi acceleration. However, this paradigm has not been verified, as key aspects of the acceleration process, such as its mechanism and efficiency, are not well understood. Shock velocity is considered as one of the key...
Imaging Atmospheric Cherenkov Telescopes (IACTs) are ideal for investigating the nature of moderately extended gamma-ray sources at very high energy thanks to their optimal angular and energy resolution compared to ground array detectors.
The Supernova Remnant SNR G106.3+2.7 is one of the most promising Galactic hadronic PeVatron candidates. We carried out observations using the Large-Sized...
In December 2023, the Flat Spectrum Radio Quasar OP 313 experienced an extraordinary very-high-energy (VHE, E>100 GeV) gamma-ray flare, reaching an integral flux of 0.3 Crab Units above 100 GeV. This event marked the first VHE detection of OP 313 by the first Large-Sized Telescope (LST-1) at the Northern site of the Cherenkov Telescope Array Observatory, delivering its inaugural scientific...
The flat spectrum radio quasar OP 313 showed intense $\gamma$-ray emission from November 2023 to March 2024, as observed by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. From that event a large number of follow-up campaigns at all wavelengths started, confirming the increase of the source activity from the radio to very high energy (VHE) bands. Remarkably, it also led...
Galactic PeVatrons are astrophysical sources accelerating particles up to a few PeV (~10^15 eV). The primary method to identify both electron and proton PeVatrons is the observation of gamma-ray radiation at ultra-high energies (UHE, E>100 TeV). In 2021, LHAASO detected 14 steady gamma-ray sources with photon energies above 100 TeV and up to 1.4 PeV. Most of these sources can be plausibly...
The origin of the highest energy (>100TeV) neutrinos is still highly debated. AGN jets are capable of accelerating hadrons to relativistic speeds, a necessary step for neutrino production in photohadronic processes. A dense photon field, such as UV emission line photons from the broad-line region, can serve as a sufficient target for photohadronic interactions to produce neutrinos. However,...
Galactic $\gamma$-ray sources can be produced by either high-energy protons via proton-proton collisions or electrons/positrons via inverse Compton scattering. Distinguishing between the hadronic and leptonic origin of $\gamma$-ray emission in Galactic sources remains challenging. Measurements of non-thermal X-ray spectra of these sources, which could originate from primary electrons in the...
The Seyfert galaxies NGC 1068 and NGC 4151 have emerged as the most promising counterparts of 4.2ฯ and 3.0ฯ neutrino excesses detected by IceCube in the TeV energy range.
Gamma rays and neutrinos are co-produced at the same flux level via hadronic interactions between the parent proton population and the ambient matter and radiation in the neutrino-emitting region.Observations of NGC 1068...
Galactic cosmic rays are widely believed to be accelerated via the diffusive shock acceleration (DSA) mechanism at supernova remnants (SNRs). However, recent observations of SNRs with ages on the order of $10^2$ to $10^3$ years suggest that the maximum energy of accelerated cosmic rays does not reach the PeV scale. In contrast, Inoue et al. (2021) demonstrated through kinetic-MHD simulations...
Novae are thermonuclear explosions occurring on the surface of a white dwarf in a binary system. These explosive events are detected across multiple wavelengths, from radio to X-rays, mostly due to thermal emission. However, in 2010, Fermi-LAT unexpectedly detected gamma-ray emission from the nova V407 Cyg, challenging prior expectations, as novae were not considered capable of accelerating...
While much work has gone into associating neutrino emission with various sources, very few sources have emerged. With the recent publication of IceCube Event Catalog (IceCat-1), the IceCube neutrino observatory has released a list of the most promising astrophysical neutrino events since operations began in 2010. Using the archival data from the High Altitude Water Cherenkov (HAWC) gamma-ray...
Cosmic rays (CRs) are among the non-thermal components of the interstellar medium (ISM) that are ubiquitous throughout the Galaxy. While CR number density can be inferred from local measurements on the Earth, their 3D distribution has largely been explored through simulations. A data-driven 3D map of CRs is essential to better understand the spatial distribution of CRs and to probe the...
The Cherenkov Telescope Array Observatory (CTAO) is the next-generation ground-based gamma-ray observatory, designed to enhance sensitivity and energy coverage (20 GeV -- 300 TeV) over current Imaging Atmospheric Cherenkov Telescopes (IACTs). The instrument's specifications will enable detailed Active Galactic Nuclei (AGN) studies in the very-high-energy (VHE) regime. Predicting the AGN...
The H.E.S.S. array of imaging atmospheric telescopes is observing the Galactic Center since more that 20 years. The H.E.S.S. collaboration carried out deep very-high-energy (VHE, E>100 GeV) gamma-ray observations in a 25 degree squared region near the Galactic centre devised to reach the best sensitivity to VHE gamma-ray diffuse emission. We report here on the detection by H.E.S.S. of a VHE...
LHAASO first detected the onset phase of the TeV afterglow from GRB221009A and observed its
temporal overlap with the prompt emission phase, thereby offering an opportunity to detect or
constrain radiation associated with rapid variability components resembling the TeV prompt
emission in the afterglow background. The detection of TeV prompt emission could open a new
window for theoretical...
The Fermi and eROSITA bubbles (FBs and eRBs) are the largest gamma-ray and X-ray emitting objects in the sky, respectively. They look like nearly symmetrical pairs of bubbles rising above and below the center of our Galaxy. The FBs extend about $50^\circ$, and their emission mechanism is under debate, whether the leptonic scenario (inverse Compton scattering by relativistic electrons) or the...
Gamma-ray bursts (GRBs) are one of the main targets for the observations of the MAGIC telescopes. As a result of the effort in improving the sensitivity of the instrument and the automatic follow-up strategy, MAGIC detected two GRBs in the very-high-energy (VHE, E>100 GeV) range, namely GRB 190114C and GRB 201216C. In GRB 190114C ($z=0.42$), the data collected by MAGIC revealed a new emission...
The gamma-ray burst (GRB) 221009A, commonly referred to as the "Brightest of all Time" (BOAT), produced photons of record TeV energies as well as an exceptionally extended afterglow across the electromagnetic spectrum. The burst was observed by the Large High-Altitude Air Shower Observatory (LHAASO) from the initial onset of very-high-energy emission (>300 GeV) until it left its field of view...
The Calorimetric Electron Telescope (CALET) currently has more than nine years of high-energy ฮณ-ray data that has not been fully explored. A region of particular interest for ฮณ-ray astronomy is the Galactic Center (GC). Analysis of Fermi Large Area Telescope (LAT) data shows an excess of GeV ฮณ rays from the GC region that could possibly be explained by the annihilation of weakly interacting...
We present results from the High Energy Stereoscopic System (H.E.S.S.) follow-up observations of Gamma-ray Bursts (GRBs) between 2004 and 2019. We are focusing on non-detections and providing the most extensive set of very-high-energy (VHE, >100 GeV) upper limits to date. We use this catalogue to constrain the properties of VHE-detected GRBs and compare them to those detected at VHE. Our study...
Imaging Atmospheric Cherenkov Telescopes (IACTs), including H.E.S.S., MAGIC, and VERITAS, have detected very-high-energy gamma rays from the central region of the Milky Way. The PeVatron hypothesis posits that the supermassive black hole Sagittarius A* (Sgr A*) accelerates cosmic rays to PeV energies, producing a diffuse gamma-ray emission extending up to tens of TeV across the central...
Recently, precision measurements of cosmic rays have revealed spectral structures that deviate from the previously assumed simple power law. These features offer a wealth of theoretical interpretations to obtain a consistent picture of cosmic ray acceleration, propagation and/or injection, including potential contributions from nearby sources. Among the different species, protons, the most...
We present a new model for the TeV afterglow of GRB 221009A. The magnetic acceleration reproduces the rapid increase of the TeV flux in the very early phase. We consider the change in the radial structure of the circumstellar medium from homogeneous to wind-like to describe the breaks in the TeV light curve. Our results imply a highly magnetized ejecta with a significantly thick width, making...
Long-duration gamma-ray bursts (GRBs) are produced with ultra-relativistic jets that emerge soon after the collapse of massive stars. The highly variable prompt-emission, lasting for a few minutes, originates from the internal dissipation within the jet. This is followed by afterglow emissions, which can persist for several days. The observed afterglow, from radio to TeV energies, is typically...
Galactic diffuse gamma-ray emission is the radiation produced by the interaction of high-energy cosmic rays propagating through the Milky Way with the interstellar gas and radiation fields. Its measurement allows for crucial insights into the acceleration and transport of cosmic rays throughout our Galaxy.
Here, we present a new analysis of the TeV Galactic diffuse gamma-ray emission using...
The fireball model has been widely used to explain the spectral energy distribution and light curves of gamma-ray bursts (GRBs) during the afterglow phase. According to this model, particles are accelerated in external shocks, resulting in photon emission via synchrotron radiation and synchrotron self-Compton (SSC) processes. However, this framework does not fully account for all observed...
Recently, the LHAASO collaboration measured the diffuse gamma-ray emission in the energy range, $10-10^3$ TeV, after masking the contribution of known sources.
The measurement is 2โ3 times higher than the gamma-ray signal expected from the hadronic interactions of diffuse cosmic rays with the interstellar medium, suggesting a possible contribution from unresolved sources.
However,...
The High-Energy Particle Detectors (HEPDs) onboard the China Seismo-Electromagnetic Satellite (CSES) mission are designed to study charged particle fluxes in space. The first-generation instrument, HEPD-01 on CSES-01, was originally conceived to measure low-energy electrons and protons but has also demonstrated the ability to detect transient phenomena such as Gamma-Ray Bursts (GRBs). By...
X-ray light curves of gamma-ray burst (GRB) afterglows exhibit various features, with the shallow
decay phase being particularly puzzling. While some studies report absence of the X-ray shallow decay
for hyper-energetic GRBs, recently discovered GRB 240529A shows a clear shallow decay phase with
an isotropic gamma-ray energy of $2.2\times10^{54}$ erg, making it a highly unusual case...
The LHAASO collaboration has recently released the spectrum and the angular distribution of the gamma-ray Galactic diffuse emission from 1 TeV to 1 PeV measured with the
Kilometer-2 Array (KM2A) and Water Cherenkov Detector Array (WCDA). We show that those data are in remarkably good agreement with a set of pre-existing models that assume the emission to be produced by the Galactic population...
The early X-ray afterglows of Gamma-Ray Bursts (GRBs), observed with the Swift X-ray Telescope (XRT; 0.3โ10 keV) onboard the Neil Gehrels Swift Observatory, have revealed distinct temporal features beyond those predicted by the standard forward shock afterglow model. Components in the XRT light curve, such as steep decay, flares, and plateaus, suggest more complex afterglow physics. These...
The diffuse Galactic gamma-ray emission, mainly produced via interactions between cosmic rays and the interstellar medium and/or radiation field, is a crucial probe of the distribution, propagation, and interaction of cosmic rays in the Milky Way. Using the source deduction method and the latest data from WCDA and KM2A, we have preliminarily measured this emission and present the energy...
In this work, we present the first example of a self-consistent 3D modeling of the VHE (>100TeV) cosmic ray (CR) distribution in our Galaxy, by injecting CRs at individual discrete transient sources in the Galactic disc, and propagating them from first principles by integrating their trajectories in models of the Galactic magnetic field. We then calculate the resulting VHE secondary gamma-rays...
The recent detection of very high-energy (VHE, $>$ 100 GeV) gamma-ray emission from gamma-ray bursts (GRBs) has provided new insights into afterglow physics. Understanding the temporal and spectral evolution of VHE GRBs requires detailed modeling and multi-wavelength observations spanning radio to VHE. The afterglow emission primarily consists of synchrotron radiation from forward and reverse...
Recent secondary-over-primary cosmic-ray (CR) ratio measurements by DAMPE and CALET show a hint of a flattening above ( \sim) TV rigidities. It is plausible - and theoretically well-motivated - that CRs accumulate additional grammage inside the source environment leading to a constant grammage in addition to the Galactic one. In this contribution, we explore this scenario, quantifying the...
The TeV gamma-ray band is essential for probing the most extreme particle acceleration processes in the Universe. The recent detections of gamma-ray bursts (GRBs) at these energies offer an incredible opportunity to investigate the origins of such transient events in an unprecedented way. In this presentation, we analyze the afterglows of these GRBs by modeling their synchrotron and inverse...
The origin of Fast Radio Bursts (FRBs) remains a longstanding and intriguing mystery. Discovering their progenitors will increase our knowledge of compact objects in extreme environments and will improve the use of these sources to probe cosmology and the structure of galaxies. A key discriminator between various models is the presence of multiwavelength counterparts. Although previous...
Recently, LHAASO has announced the highest-energy measurements of the diffusive gamma-ray flux, offering the possibility of probing the spatial distribution and energy spectrum of the galactic cosmic rays (CRs) up to the all-particle spectrum knee ($\sim 4$ PeV). However, a persistent tension between observations by experiments (such as Fermi and LHAASO) and the predictions based on...
Diffuse emission in gamma-rays and neutrinos are produced by the interaction of cosmic rays with the interstellar medium. Below some hundreds of TeV, the sources of these cosmic rays are most likely Galactic. Hence, observations of high-energy gamma-rays and neutrinos can be used to probe the flux of cosmic rays in other parts of the Galaxy. Supernova remnants are usually considered as the...
Fast Radio Bursts (FRBs) are brief, highly energetic radio flashes of unknown origin. Their high luminosity, short duration, and large dispersion measures suggest an extragalactic origin, potentially linked to extreme astrophysical objects such as magnetars. The growing number of detected FRBs, including repeating sources, has driven extensive multi-wavelength follow-up efforts. While FRB...
Gamma-ray bursts (GRBs) are bright flashes of electromagnetic radiation originating from the core collapse of massive stars or the merger of compact objects. It has long been theorized that GRBs can emit very high-energy (VHE) gamma rays that can reach the TeV level. Although current-generation Imaging Atmospheric Cherenkov Telescopes (IACTs), such as H.E.S.S., have been observing GRBs since...
The spatial diffusion of energetic particles in a magnetic field composed of a large-scale background and a small-scale turbulent component should be expected to be anisotropic. While such anisotropic diffusion has been known for quite a while in first-principle plasma physics and while it is required for an understanding of the transport of cosmic rays in the heliosphere or close to supernova...
Galactic diffuse gamma-rays emission (GDE) in the sub-PeV energy range (E > 100 TeV = $10^{14}$ eV) was first detected by the Tibet AS$\gamma$ experiment in 2021, ensuring the presence of PeV cosmic-ray accelerators in the Galaxy. On the other hand, in 2023 the Large High Altitude Air Shower Observatory (LHAASO) detected GDE covering an energy range between 10 TeV and 1 PeV. Interestingly, the...
Gamma-ray bursts (GRBs) are the most powerful transient explosions in the Universe and emit a vast amount of their energy in the form of gamma-rays. Although they last extremely short on cosmic time scales, their gamma-ray emission shows a wealth of temporal variability. Properties of this variability may carry information about the processes the gamma-rays emerge from, which remain poorly...
Gamma-ray bursts (GRBs) originate from explosions at cosmological distances, generating collimated jets. GRB 221009A, triggered on 9 October 2022, has been established as the brightest GRB to date. Its bright and long emission was extensively followed up from radio to gamma rays. LHAASO firmly detected the onset of the afterglow emission at energies up to ~13 TeV within about an hour after the...
Galactic diffuse gamma-ray emissions have been observed from MeV to PeV energies.
These emissions are connected via a common origin of the cosmic ray (CR) particles, but the energy dependence and hadronic/leptonic fraction remain unconstrained.
We model the Galactic CR distributions and associated non-thermal diffuse emissions from TeV--PeV energies using the GALPROP framework.
We...
The recent detections of the afterglow phase of long gamma-ray bursts (lGRBs) at very high energies (VHE, >100 GeV) mark a significant advance in astrophysics of transient phenomena, offering deeper insights into the acceleration mechanisms, jet structure, and physical processes driving GRB emission. In the multi-messenger landscape, both high-energy neutrino and gravitational-wave detections...
Extended very-high-energy gamma-ray emission from middle-aged pulsars as revealed recently by several groundbased gamma-ray experiments has strong implication on the transport of high-energy particles in the interstellar medium surrounding those pulsars. The gamma-ray emission is widely believed to be produced by high-energy electrons and positrons accelerated by the pulsar wind nebulae when...
We calculate the high-energy gamma-ray and neutrino emissions from galaxy clusters like Perseus that host active galactic nuclei (AGNs). Our primary objective is to distinguish the emission from the central source, such as NGC1275, from the diffuse emission originating in the outskirts of the Perseus cluster. Due to unique magnetic-field configuration, CRs with energy โค 10^17 eV can be...
Galaxy clusters are the most massive gravitationally bound structures in the Universe. Even if clusters are nearly virialized structures, they undergo merging processes, creating merging shocks, and suffer from feedback from galaxies and AGNs; causing complex turbulent motions and amplifying their magnetic fields. These processes act as acceleration mechanisms for the plasma of the...
In this talk, we report the discovery of an extended very-high-energy (VHE) gamma-ray source around the location of the middle-aged (360 kyr) pulsar J1846+0919 with LHAASO. The source is detected with a significance of 7 ฯ for E>10 TeV assuming a Gaussian template. The best-fit position is (RA, Dec) = 281ยฐ.90ยฑ0ยฐ.21, 9ยฐ.44ยฑ0ยฐ.17, and the extension is 0ยฐ.88ยฑ0ยฐ.17. The spectrum can be described...
Pulsar halos are a recent class of extended very high-energy (VHE) sources discovered by the HAWC observatory towards the Geminga and Monogem pulsars. These VHE sources are interpreted as the inverse Compton emission from electrons and positrons diffusing in the interstellar medium at an inhibited rate, having escaped the pulsar wind nebula. Our aim is to search for new pulsar halos using...
In this contribution, we present a search for dark matter signatures from the Virgo Cluster using over 200 hours of observations with the H.E.S.S. Imaging Atmospheric Cherenkov Telescope Array. Galaxy clusters provide an ideal environment for investigating potential dark matter interactions, whether through particle decay or annihilation, which could generate a persistent flux of...
Geminga is the first pulsar around which a remarkable TeV gamma-ray halo extending over a few degrees was discovered by MILAGRO, HAWC and later by H.E.S.S., and by Fermi-LAT in the GeV band. Similar emission has been detected for other middle-aged pulsars in their late evolution stages, and is most plausibly explained by inverse Compton scattering of CMB and interstellar photons by...
The dominant mechanisms underlying the high-energy gamma-ray emission from galaxies vary with galaxy types. In starburst galaxies, a substantial component arises from neutral pion decays. These are driven by interactions of hadronic cosmic rays (CRs) accelerated in strong shocks associated with the star formation process and its end-products. Leptonic gamma-rays may also originate from...
The growing number of starburst galaxies detected by the current generation of gamma-ray detectors has brought this class of objects to the forefront of cosmic-ray research. The VERITAS collaboration has performed very-high-energy (VHE; E>100 GeV) gamma-ray observations of a variety of starburst galaxies as part of a long-term program. The selection of these targets is based on either a high...
Pulsar halos are a recently identified class of TeV ฮณ-ray sources, offering valuable insights into the evolution of pulsar systems at the highest energies. However, only a handful of such sources have been detected so far, making each new identification critical for understanding the properties of the population as a whole. We report the first detection of extended very-high-energy (VHE) ฮณ-ray...
A major fraction of gamma-ray sources in the non-thermal universe are pulsar wind nebulae (PWNe), which evolve rapidly and exhibit distinct morphological and spectral features at different evolutionary stages. LHAASO has identified dozens of TeV sources associated with pulsars, which are potential candidates for PWNe or halos. In this study, we use LHAASO data to investigate the relationship...
The blazar OT 081 was detected only once in the very-high-energy gamma-rays range, by MAGIC and H.E.S.S. telescopes. The multiwavelength (MWL) data collected in that single opportunity, and reported in a recently published paper (Abe et al. 2025, "Multi-wavelength study of OT 081: broadband modelling of a transitional blazar"), show a challenging theoretical interpretation because of the high...
The presence of slow diffusion regions as a possible explanation for extended TeV emission around pulsars such as Geminga, Monogem, and PSR J0622+3749, as well as for the X-ray filaments surrounding bow shock pulsar wind nebulae like the Guitar Nebula, PSR J2030+4415, and the Lighthouse Nebula, challenges the conventional understanding of the cosmic ray diffusion coefficient in the...
Star-forming galaxies (SFGs) are considered to be an important component of the diffuse extragalactic gamma-ray background (EGB) radiation observed in 0.1 -- 820 GeV, but their quantitative contribution has not yet been precisely determined. In this study, we aim to provide the currently most reliable estimate of the contribution of SFGs based on careful calibration with $\gamma$-ray...
There has been ongoing debate about the potential unconfirmed asymmetric structure of the diffuse $\gamma$-ray emission of the Geminga halo. In this work, we adhere to first principles, injecting and propagating individual cosmic ray (CR) electrons in 3D realizations of turbulent magnetic fields characterized by Kolmogorov turbulence and Bohm diffusion. The particle motion is governed by the...
More than a decade ago, the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope unveiled the existence of two gigantic gamma-ray lobes known as the Fermi bubbles. While their origin is still unknown, various studies identified intricate spectral and morphological structures within the bubbles. One peculiar region, the cocoon, has recently been associated with gamma-ray...
Cosmic ray (CR) hadrons with GeV-PeV energies are expected to reside in the circumgalactic medium (CGM) around the Milky Way (MW), having escaped from the Galactic disk, or injected in situ by satellite galaxies, large scale shocks due to Galactic winds, etc. In some cases, circumgalactic CRs (CGCRs) may play important thermal and dynamical roles in the evolution of galaxies, but observational...
Since the discovery of TeV halos around the Geminga and B0656+14 pulsars by the HAWC experiment in 2017, and around J0622+3749 by LHAASO in 2021, several theoretical efforts have been dedicated to understanding this source class. Surprisingly, the gamma-ray emission hints at a strong confinement of high-energy electron-positron pairs around the pulsar, which challenges our current...
Pulsar associations constitute the most numerous class of Galactic TeV sources, with pulsar wind nebulae (PWNe) and pulsar halos playing a crucial role in high-energy astrophysics. We build a population synthesis pipeline based on the COMPAS code to model stellar evolution and pulsar populations. Our framework tracks the evolution of pulsars through various PWN and pulsar halo stages,...
The gravitationally lensed blazar PKS 1830-211 underwent a historically bright and unusually long-duration gamma-ray flaring episode in 2019/2021 with daily fluxes exceeding > $10^{-6}$ ph/cm$^2$/s for ~400 days, and daily peak fluxes (> $10^{-5}$ ph/cm$^2$/s) exceeding all prior flares observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope in the first 15...
The recent discovery of multi-TeV pulsed emission from Vela and PSR J1509-5850 represents a major breakthrough in pulsar physics. We present the latest findings from very high-energy (VHE) observations using the H.E.S.S. telescopes and discuss key similarities and differences in the emission properties of these two pulsars in the GeV and multi-TeV ranges, in relation to their main...
Lorentz invariance violation (LIV) can have multiple consequences on very-high energy gamma raysโ emission, propagation, and detection, such as energy-dependent photon group velocity, photon instability, vacuum birefringence, and modified electromagnetic interaction. Depending on the underlying theoretical model, several of these effects can coexist. Nevertheless, in experimental tests of LIV,...
We report the discovery of an extended ฮณ-ray source named LHAASO J0534+3535 with a significance of about 8 standard deviations for energy from TeVs to tens of TeVs. In addition to the ฮณ-ray source detected by LHAASO, there is only one old supernova remnant candidate, G172.8+1.5, and two 4FGL GeV sources identified within a 4-degree radius of LHAASO J0534+3535. G172.8+1.5 is located in one of...
The Major Atmospheric Cherenkov Experiment (MACE) has been conducting
regular observations of very high-energy (VHE) gamma-ray sources since
2021. MACE has successfully detected gamma-ray emission from the standard
candle Crab Nebula, with its measured differential energy spectrum in
agreement with earlier results from similar telescopes. In addition to the
Crab Nebula, MACE has also...
The High Altitude Water Cherenkov (HAWC) Observatory has identified three TeV gamma-ray sources in the DA 495 region, a complex area of the Galactic plane that includes the pulsar wind nebula candidate DA 495 and other sources. In this talk, I will present an updated analysis of the morphology and energy spectra of these sources using 2860 days of HAWC data processed with an improved...
The Tibet AS$\gamma$ experiment, observing cosmic rays/gamma rays above a few TeV, is located at 4,300 m above sea level, in Tibet, China. The experiment is composed of a 65,700 m$^{2}$ surface air shower array and 3,400 m$^{2}$ underground water Cherenkov muon detectors. The surface air shower array is used for reconstructing the primary particle energy and direction, while the underground...
The LHAASO~J2018+3651 region is one of the brightest sources in the sky at TeV energies. Photons with energies up to โผ0.27 PeV from this region have been detected with the Large High Altitude Air Shower Observatory (LHAASO) and here we present a detailed study of this region using more data from LHAASO. This analysis resolves the region into six sources: LHAASO~J2018+3641, LHAASO~J2019+3649,...
The GRAPES-3 experiment, located at an altitude of 2200 metres in, Ooty, Southern India (11.4ยฐN, 76.7ยฐE, 2200 m a.s.l.), records extensive air showers in the TeVโPeV energy range using an array of 400 plastic scintillator detectors arranged in a hexagonal grid over an area of 25,000 mยฒ, along with a 560 mยฒ muon detector made of proportional counters. The latter allows showers initiated by...
The High Energy Stereoscopic System (H.E.S.S.) collaboration reported the emission of two extended sources, HESS J1857+027 and HESS J1858+020, with no known counterparts with an approximate separation of 1 degree. However, in the 3HWC catalog, the High-Altitude Water Cherenkov (HAWC) collaboration reported the emission of 3HWC J1857+027. We present a multi-source fitting analysis of the HESS...
We present an updated catalog of TeV gamma-ray sources using data from the 5th reconstruction pass of data from the High Altitude Water Cherenkov Observatory (HAWC). In addition to improved reconstruction and nearly three years of additional data, this new catalog uses a systematic multi-source fitting procedure to model the data with much greater flexibility and accuracy. Besides including a...
HESS J1857+026 remains a mysterious gamma-ray emitter since its discovery in 2008. Despite the disclosure of a nearby pulsar and multiple studies in the high-energy (HE, E > 100 MeV) and very-high-energy (VHE, E > 100 GeV) regimes, there have been no confirmed counterparts (e.g., an SNR shell or other extended structure) in X-ray or other wavelengths. We present the result of our study of the...
The current Fermi-LAT source catalog (4FGL-DR4: 7194 sources over 14 years) was built incrementally from the 8-year catalog by adding newly discovered sources but keeping the positions of existing sources fixed. Now, after 16 years (reached in August 2024) there are twice as many data as used in the original 4FGL catalog, enabling much more precise source positions. It is thus time to...
Over the past 16 years, the Fermi Large Area Telescope (LAT) has significantly advanced our view of the GeV gamma-ray sky, yet several key questions remain - such as the nature of the isotropic diffuse background, the properties of the Galactic pulsar population, and the origin of the GeV excess towards the Galactic Centre. Addressing these challenges requires sophisticated astrophysical...
Imaging with Cherenkov telescopes was a breakthrough for gamma ray astronomy. However, by pushing Cherenkov telescopes to ever higher precision and ever larger sizes our upcoming generation of telescopes has reached the intrinsic limits of imaging itself. Aberrations limit our field-of-view and the angular resolution in the gamma-ray sky. The square-cube-law escalates the costs to construct...
Microquasars have been shown to be capable to accelerate particles to energies well above 100~TeV. The reported presence of hadronic particles in their jets makes them one of the most convincing PeVatron candidates. Their proximity to Earth allows detailed studies of their morphology, providing unique laboratories for the study of particle acceleration in jets. The LHAASO Observatory has...
Ground based gamma ray measurements with IACTs suffer from irreducible backgrounds from a specific type of cosmic-ray induced air showers. These air showers are characterized by a large electromagnetic component which is mostly due to highly energetic neutral pions produced in the primary interaction of cosmic rays with atmospheric nuclei. Current event generators that model these hadronic...
The detection of very high-energy (VHE) and ultra-high-energy (UHE) emissions associated with micro-quasars has unveiled a new class of powerful particle accelerators. The particles are suggested to be accelerated within their jets or surrounding environments. Cygnus X-1 and Cygnus X-3 are two prominent micro-quasars located in the Cygnus region. Significant efforts have been dedicated to...
Very high-energy gamma-ray emission from the microquasar V4641 Sgr with energy up to beyond 100 TeV has been recently detected with the H.E.S.S., HAWC, and LHASSO observatories. The gamma-ray emission reveals a puzzling 200-parsec-long structure significantly misaligned with its radio jet. We propose that this gamma-ray structure is produced by high-energy cosmic-ray particles escaping from...
The current generation of Imaging Atmospheric Cherenkov Telescopes (IACTs: HESS, VERITAS and MAGIC) has led to a renaissance in the use of stellar intensity interferometry for sub-milliarcsecond optical astronomy. This technique, used over distances of O(100 m) between telescopes, enabled the measurement of stellar radii on the order of a few hundred micro-arcseconds with a ~10% resolution...
A fundamental challenge for observations with Imaging Atmospheric Cherenkov Telescopes is the treatment of the dominant background of cosmic-ray initiated air showers. Traditional frequentist methods for signal estimation rely on gamma-hadron separation cuts to remove a large fraction of background events (reducing the efficiency of gamma-ray detection). In this work we adopt and extend a...
Microquasars are powerful cosmic particle accelerators within our galaxy, known for emitting gamma rays at energies beyond the multi-teraelectronvolt (TeV) range. Whether they can accelerate particles to PeV energies and qualify as PeVatrons remains an open question, with SS 433 being the only confirmed TeV-emitting microquasar. The High-Altitude Water Cherenkov (HAWC) Observatory has first...
Imaging atmospheric Cherenkov telescopes (IACTs) detect extended air showers (EASs) generated when very-high-energy (VHE) gamma rays or cosmic rays interact with the Earth's atmosphere. Cherenkov photons produced during an EAS are captured by fast-imaging cameras, which record both the spatial and temporal development of the shower, along with calorimetric data. By analyzing these recordings,...
Recently, LHAASO published its measurement of the Galactic diffuse gamma-ray emission in the $\rm{TeV}-\rm{PeV}$ range, which seemed to be $2$ to $3$ times higher than theoretical expectations. To explain the apparent discrepancy, an important contribution from a population of unresolved pulsars or important spatial variations in the cosmic-ray density have been proposed. We show through a...
Deep learning techniques have continued to evolve and find novel applications across scientific disciplines, and Graph Neural Networks (GNNs) have emerged as a high-performance architecture particularly suited for datasets with irregular topology. The MAGIC Telescope, comprising a pair of 17 m Imaging Atmospheric Cherenkov Telescopes (IACTs) located at Roque de Los Muchachos Observatory in La...
Cygnus X-3 is a microquasar consisting of a compact object of unknown nature and a Wolf-Rayet star, which orbit each other with a very short period of 4.8 hours. The compact object launches powerful jets that are an excellent site for particle acceleration up to relativistic energies. The presence of these relativistic particles, combined with the proximity to the star and its high luminosity,...
The study of gamma-ray binaries using LHAASO data provides crucial insights into high-energy astrophysics. These binaries, consisting of a massive star and a compact object, emit radiation primarily in the MeV to TeV range. LHAASOโs sensitivity enables detailed observations of key sources, including HESS J0632+057, PSR J2032+4127, GRS 1915+105, SS 433 (w1 & e1), and LS I +61 303, each...
While Supernova Remnants (SNRs) are widely considered the primary accelerators of cosmic rays (CRs) up to hundreds of TeV, they struggle to account for the CR flux at PeV energies, suggesting the existence of additional PeVatrons. Observations from LHAASO have identified several PeVatron candidates, including some SNRs, pulsar wind nebulae, TeV halos and young massive star clusters (YMSCs)....
LS 5039 is a High Mass X-ray Binary (HMXRB) comprising a compact object in an eccentric 3.9 day orbit around a massive O6.5V star. It is one of the most studied object in the field. A first HESS publication in 2004 established multi-TeV emission from the system (first ever TeV binary system). A second publication in 2006 , based on a deeper data set of โผ 70h of observation, established the TeV...
An international collaboration composed of Italian, Japanese, Spanish and Swiss institutes, is developing the advanced camera (AdvCam), the next-generation camera for Imaging Atmospheric Cherenkov Telescopes, designed specifically for the Large-Sized Telescopes (LST) of the Cherenkov Telescope Array Observatory. AdvCam incorporates cutting-edge Silicon Photomultipliers (SiPMs) and a fully...
The binary LS I +61$^{\circ}$ 303 was discovered as a gamma ray emitter nearly fifty years ago and has since been the subject of extensive observations across the electromagnetic spectrum. Composed of a primary Be star and a neutron star, LS I +61$^{\circ}$ 303 exhibits complex periodic behavior and variability from radio wavelengths to very-high-energy gamma rays (VHE, E>100 GeV), with...
The AdvCam is a next-generation camera for the Large-Sized Telescopes of the Cherenkov Telescope Array Observatory, based on silicon photomultipliers. Its fully digital readout system enables the design of new, sophisticated trigger logic.
The Large-Sized Telescopes aim to cover the low-energy range of the cosmic gamma-ray spectrum, with a threshold starting at about 20 GeV, using the...
HAWC and LHASSO reported very high energy (VHE) gamma rays with energies exceeding 100 TeV from five Galactic black hole binaries. The spatial extent of the VHE gamma rays is several tens of pc, which is much larger than the size of a black hole binary system. Some black hole binaries have different gamma-ray spectra, some of which are steeper than predicted by the standard shock acceleration...
We have built a prototype of stereoscopic water Cherenkov detector array (SWCDA) inside the Tibet ASgamma air-shower array (Tibet-III array) by the end of 2024. The SWCDA project is the next generation of innovative ground-based stereoscopic water Cherenkov detection array, its main scientific goal is to observe 100GeV-10TeV high-energy gamma-ray astronomy, such as observation of blazars,...
Microquasars are increasingly recognized as efficient particle accelerators, potentially contributing to the cosmic-ray flux up to the knee. Among them, SS 433 stands out as a unique system with precessing relativistic jets embedded within the W50 supernova remnant. Recent detections of very-high- and ultra-high-energy (UHE) gamma rays from SS 433 have solidified its role as a key laboratory...
The project Probing Extreme PeVatron Sources (PEPS) aims at measuring the most energetic $\gamma$-rays from our Galaxy in the energy range between $10^{15}$ eV and $5\times 10^{16}$ eV, opening a new energy window for multimessenger astroparticle physics. PEPS will consist of an array of 10 km$^2$ placed in the southern hemisphere, at the location of the Pierre Auger Observatory. It will be...
Since the recent detection of very-high-energy (VHE; $E>0.1$ TeV) gamma rays, microquasars have gained more and more attention as potential PeVatron candidates. Among them, the microquasar SS 433 and its nebula W50 stand out as the first to be detected in VHE gamma rays. HAWC and H.E.S.S. reported TeV gamma-ray emission from knot-like structures in the outer lobes, likely powered by jets...
By analyzing the radio emissions from air showers using interferometry, we can estimate their properties. In this contribution, we apply interferometry to reconstruct air-shower parameters based on measurements taken with the Auger Engineering Radio Array (AERA) at the Pierre Auger Observatory. This reconstruction method is achievable at AERA through precise clock synchronization with a beacon...
