The High Altitude Water Cherenkov (HAWC) observatory is highly suitable for large-scale survey work. The high duty time (95+%), large instantaneous FoV (2 sr), and sensitivity over the 300 GeV to more than 100 TeV energy range make it ideal for creating a catalog of very high energy (VHE) sources. Over the lifetime of the HAWC observatory, 4 catalogs have been produced 3 of which were...
The fourth release of the Fourth Catalog of Fermi-LAT Sources (4FGL-DR4), based on 14 years of data between 50 MeV and 1 TeV, is presented. Improvements in the analysis method relative to the original 4FGL catalog and new features are reviewed. The 4FGL-DR4 includes about 500 more sources than the previous release (4FGL-DR3, obtained with 12 years of data) and about 2100 more sources than...
The Crab pulsar (PSR J0534+2200), whilst being among the best studied objects in the sky, still challenges our understanding of the very-high-energy (VHE) emission processes in pulsars. Pulsed gamma rays are detected beyond 1 TeV, with a phase-folded lightcurve that presents two characteristic peaks joint by a "bridge". The trailing peak progressively becomes more dominant as energy increases...
The next generation ground-based instrument for very-high-energy gamma-ray observations will be the Cherenkov Telescope Array Observatory (CTAO). At one of the two planned sites, La Palma (Canary Islands, Spain), the first prototype of a Large-Sized Telescope, LST-1, is already operational and is currently under commissioning. The two MAGIC Cherenkov telescopes have been operating in...
The Crab pulsar wind nebula is one of the best-studied objects in the gamma-ray sky. Recently, its angular extension in the gamma-ray domain could be resolved in separate analyses of Fermi-LAT and H.E.S.S. data, which provides crucial information about the spatial distribution of relativistic particles in the nebula. In this contribution we provide, for the first time, a measurement of the...
Reverberation starts when the PWN is reached by the reverse shock of the supernova remnant. Depending on the internal to the outer pressure balance, it might induce a compression of the PWN. This period has a large (even huge) effect on the subsequent dynamical and spectral evolution.
In this talk, we shall present numerical evidence for that the shell accumulated at the PWN boundary is far...
The luminous pulsar wind nebula (PWN) HESS J1825-137 was the first object in gamma-ray astronomy that was discovered to have energy-dependent morphology. In addition to its detection and this discovery by H.E.S.S., J1825-137 and the region around it have been explored and characterized also using the VERITAS, Fermi-LAT, HAWC, and LHAASO instruments. Its exceptional TeV luminosity has been...
W44 is a middle-aged Supernova Remnant (SNR) largely investigated to probe acceleration of Cosmic Rays (CRs). Previous studies already showed the presence of gamma-ray emission not only from the remnant, but also from its surroundings, thought to be due to high-energy CRs escaping from the forward shock of the remnant.
We present a detailed morphological and spectral analysis of Fermi-LAT...
Galactic pulsars, such as Geminga, are surrounded by a bright and extended TeV emission. This radiation is compatible with multi-TeV electrons scattering off low-energy photons via the inverse-Compton scattering process. To date, about 10 TeV halos have been observed around known pulsars. Next-generation gamma-ray detectors, such the Cherenkov Telescope Array (CTA), will have unprecedented...
Observations by the HAWC and HESS telescopes have found extended TeV emission consistent with a handful of young and middle-aged pulsars. In this talk, I will show that these detections have significant implications for our understanding of both pulsar emission and TeV astrophysics. Most importantly, the high-luminosity and spatial extension of TeV halos indicate that cosmic-ray diffusion on...
The 𝛾-ray emission from stars is induced by the interaction of cosmic rays with stellar atmospheres and photon fields. This emission is expected to come in two main components: a stellar disk emission, where 𝛾-rays are mainly produced in atmospheric showers generated by hadronic cosmic rays, and an extended halo emission, where the high density of soft photons in the surroundings of stars...
Although supernova remnants are thought to be responsible for the bulk of the flux of cosmic rays in our Galaxy, their ability to produce the highest-energy Galactic cosmic rays is challenged by observations. Measurements of TeV gamma rays from several supernova remnants suggest cut-offs in the underlying particle spectra significantly below PeV energies. On theoretical grounds, young massive...
In the last decades, several young massive star clusters (YMSC) have been associated with extended $\gamma$-ray sources, suggesting that some acceleration process, able to produce particles at least up to hundreds of TeV, is at work. The number of YMSCs exhibiting $\gamma$-ray emission is around ten, while the possible sources amount to a significantly higher number, potentially reaching...
Novae have been recently established as prompt gamma-ray sources in the GeV energies, and also in one case in the TeV energies (RS Oph), lasting for a few days up to a month after the nova optical outburst. We consider a scenario in which electrons, accelerated continuously in the expending nova shell, escape into the surrounding medium forming an extended nebula around recurrent nova....
Gamma-ray observation in the sub-PeV range provides a method of investigating accelerators of the Galactic PeV cosmic rays, so-called PeVatrons. However, the detection of PeVatrons has not been established yet, and a large fraction of sub-PeV gamma-ray sources still has an unknown origin, which requires detailed studies for individual gamma-ray sources. A TeV gamma-ray source HESS J1843-033 is...
The Galactic Center is one of the most studied regions of the sky. Of particular interest is the supermassive black hole Sagittarius A*, whose proximity provides an opportunity for morphological investigations into the acceleration of cosmic rays in an extreme environment. Previous observations with very-high-energy gamma rays, in particular the detection of a diffuse emission component on a...
Supernova Remnants (SNRs) are the primary suspect among Galactic sources to accelerate particles via diffusive shock acceleration up to the necessary PeV energies.The gamma-ray emission of SNRs can provide direct evidence of leptonic (inverse Compton and bremsstrahlung) and hadronic (pion-decay from proton-proton interactions) processes.
Puppis A is a middle-aged SNR interacting with...
A new supernova remnant (SNR) was recently detected at radio frequencies with ASKAP at (l, b) = (288.8, -6.3) by Filipovic et al. 2023 (submitted), partly coincident with a Fermi-LAT extended source that was provisionally associated with a molecular cloud. We reanalysed the region around the SNR using Fermipy, taking 14.5 years of data in a ROI of 12°.
Extended emission from the region was...
The region corresponding to the Centaurus Galactic spiral arm tangent of our galaxy, within 1 deg radius around Galactic longitude 312º, harbours a rich environment with candidate sources for gamma-ray astronomy. In particular, it contains five pulsars, with spin-down powers ranging between 10^35 and 10^37 erg.s−1, and characteristic ages between 13.6 and 62.8 kyr. The possible presence of...
The SNR G106.3+2.7, with its associated molecular cloud complex, is one of the candidate TeV counterparts of LHAASO J2226+6057, one of the 12 LHAASO Galactic Pevatrons. The other candidate is the Boomerang PWN, associated with the PSR J2229+6114. Different gamma-ray facilities have detected this VHE region with an elongated morphology: the SNR is located in the "tail" of the VHE emission and...
The recent detection of 12 gamma-ray Galactic sources well above $E>100$ TeV by the LHAASO observatory has been a breakthrough in the context of Cosmic Ray (CR) origin search.
Although most of these sources are unidentified, they are often spatially correlated with leptonic accelerators, like pulsar and pulsar wind nebulae (PWNe). This dramatically affects the paradigm for which a gamma-ray...
The detection of 14 ultra-high-energy (UHE, photon energy above 100 TeV) gamma-ray sources by LHAASO has opened up new avenues for investigating Galactic PeVatrons. We present the status of a VERITAS study of three intriguing LHAASO sources: J2108+5157, J0341+5158, and J0621+3755. J2108+5157 and J0341+5158 are "dark PeVatrons" without any source association. J0621+3755 is a TeV halo candidate...
Gamma-Ray Bursts (GRBs) are among the brightest and most energetic events in the Universe, in the form of violent extragalactic explosions of gamma rays, which are detected at the top of the Earth’s atmosphere by high-energy photon detectors. Although not specifically designed for gamma-ray detection, the High-Energy Particle Detector (HEPD-01), operational since 2018 on a low-Earth orbit,...
The detection of GRBs at very high energy (> 100 GeV) was a long-awaited result, and many observations by multiple instruments were needed before achieving this goal. The study presented here for the first time is based on a complete re-analysis of 15 years of H.E.S.S. GRBs observations, aiming to understand the reasons behind the previous lack of detections.
Through the utilisation of...
High-energy gamma rays are extremely important for the interpretation of explosive cosmic events related to the formation of neutron stars and black holes. The long-duration gamma-ray burst GRB 221009A was a recent powerful event that - with its remarkable intensity, spectral features, and duration - was clearly detected also by the AGILE satellite in the MeV-GeV energy range. Through its...
Starting from the first unequivocal detection of very high energy (VHE) emission from the luminous gamma-ray burst (GRB) GRB 190114C by the MAGIC telescopes, five detections of VHE emission from GRBs by ground-based instruments were reported as of today. Such new energetic components have become a new probe to explore GRB physics. GRB 201015A was a long GRB detected by the Swift/BAT and we...
In gamma-ray bursts, X-ray afterglows frequently show a shallow decaying emission in their first few thousand seconds. Possible models for the shallow decay phase are continuous energy injection, late catch-up of lately launched ejecta, the evolution of microscopic parameters, thin wind profile of the circumstellar medium, and so on. Depending on the models, the TeV emission of the early...
Gamma-ray bursts (GRBs) are the most luminous explosions in the Universe. Thanks to the recent observations by ground-based gamma-ray telescopes, we now know that at least a class of GRBs are able to emit very-high-energy (VHE) gamma-ray emission. Starting from GRB 190114C detected by the MAGIC telescopes, in total there are five reports of VHE detection so far from MAGIC, H.E.S.S. and LHAASO....
The search for multi-wavelength counterparts to fast radio bursts (FRBs) remains critical for understanding the underlying emission mechanisms of these interesting cosmological probes. The deepest limits come from telescopes with the fastest sampling rates in every band, meaning Imaging Atmospheric Cherenkov Telescopes (IACTs) are some of the most effective instruments to investigate these...
Gamma-ray flares from Active Galactic Nuclei (AGN) show substantial variability on ultrafast timescales (i.e. shorter than the light crossing time of the AGN's supermassive black hole). I will show that ultrafast variability is a byproduct of the turbulent dissipation of the jet Poynting flux. Due to the intermittency of the turbulent cascade, the dissipation is concentrated in a set of...
SST-1M is a single-mirror Small Size Telescope prototype developed by a consortium of institutes from Poland, Switzerland and the Czech Republic. The design of the SST-1M follows the Davies-Cotton design, with a 9.42m$^2$ multi-segment mirror. With a wide field of view of 9 degrees, SST-1M is designed to detect gamma rays in the energy range between 1 and 300 TeV. The two SST-1Ms that have...
Jetted AGNs, also called blazars when the jet is oriented toward the observer, are the brightest persistent γ-ray sources in the extragalactic sky.
The next generation Cherenkov Telescope Array Observatory (CTAO) will include telescopes with three different size to cover the full range of energy (from 20 GeV up to 300 TeV) in order to reach unpreceded capabilities in the observation of the...
The next generation facility for gamma-ray ground-based observations is the Cherenkov Telescope Array (CTA) observatory, which encompasses three distinct sizes of imaging atmospheric Cherenkov telescopes (IACTs). Among these, the Large-Sized Telescopes (LSTs) of CTA, featuring a mirror dish with a diameter of 23 meters, are engineered to detect the faint atmospheric showers from the lowest...
The most recent catalog of extragalactic gamma-ray sources, based on data collected over a period of 10 years by the Fermi satellite, double its cataloge the number of blazars with respect to the previous catalog.
In this contribution, we study the updated blazar sequence built with this extended dataset and investigate the properties of the TeV-detected subsample of sources.
This study...
The Spectral Energy Distribution (SED) of blazars consists of two components. The low-energy emission, extending from radio to X-rays, is interpreted as synchrotron radiation from accelerated electrons, while the high-energy radiation, which can reach TeV energies, is produced via inverse Compton scattering of the electrons by lower-frequency photons. The latter can come either from the...
Observational studies have revealed correlations between the fluxes of X-rays and TeV gamma-rays in blazars, particularly in the context of the leptonic Synchrotron Self-Compton (SSC) model. The HBL blazar Mrk 421 exhibits a linear correlation between these two energy ranges, although it breaks down at the highest gamma-ray fluxes, suggesting the involvement of additional mechanisms like...
Blazars are among the most intensively studied sources in high-energy astrophysics. Nevertheless, the exact acceleration processes of high-energy particles and emission mechanisms remain unclear. The recently launched IXPE satellite allows for the first time the measurement of polarisation in the X-ray band, hence opening a new window to the cosmos. The two TeV archetypical blazars Mrk421 and...
Relativistic outflows or jets with more than 99% of the light speed emerge in pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei. Such relativistic jets are thought to be launched through magnetic processes, which implies magnetically dominated outflows. However, a multi-wavelength spectrum suggests that jets must be kinetically dominated at the gamma-ray emission region. This...
M87 was discovered as a very-high-energy gamma-ray emitter (VHE, E > 100 GeV) with HEGRA in 2003, even before its high-energy gamma-ray emission (HE, E > 100 MeV) was detected. These observations established M87 as the first extragalactic source with a tilted jet detected up to the TeV energies. After the major VHE flares in 2005, 2008, and 2010, M87 has been mainly observed in a quiescent low...
The emission mechanisms and regions of multi-wavelength photons from radio galaxies are unknown. The emission from Magnetically Arrested Disks (MADs) with strong magnetic fields at the center of radio galaxies can explain the high-energy gamma-ray data, but the MAD model cannot explain the observational X-ray data. One possible scenario to explain radio to X-ray data is the emission from jets....
NGC1068 is a Seyfert II starburst galaxy emitting in a very broad range of frequencies, from radio up until gamma-ray energies. Since the observed high-energy neutrinos and gamma-rays fluxes are different by at least 2 orders of magnitude, it becomes necessary to account for a multi-component model to describe the multimessenger emission by NGC1068. The neutrinos signal can be explained...
PKS 1510-089 is the only known flat spectrum radio quasar with persistent very-high-energy (E>100GeV) gamma-ray emission. It also showed varying and complex variability and correlation patterns, which were hard to explain within a single-zone emission model. Here, we present recent observations with H.E.S.S., Fermi, Swift, ATOM and SALT. These suggest that PKS 1510-089 used to have at least...
In this study, we systematically studied the X-ray to GeV gamma-ray spectra of 61 Fermi/LAT-detected radio galaxies. We found an anticorrelation between peak frequency and peak luminosity in the high-energy spectral component of radio galaxies, similar to blazars. With this sample, we also constructed a gamma-ray luminosity function (GLF) of gamma-ray-loud radio galaxies. We found it is a...
The catalog of TeV-emitting sources (TeVCat) comprises six Fanaroff-Riley type I (FR I) radio galaxies. Unlike blazars, the jets of radio galaxies point away from the observer’s line of sight. Therefore, despite their small number, these sources, not entirely dominated by the jet component, offer a unique opportunity to investigate high-energy processes from a different perspective.
Among...
Standard models of the large-scale interstellar emission officially adopted so far for studies of the Fermi-LAT data are very uncertain and show some discrepancies with respect to the data especially in the inner Galaxy where the degeneracy with the various components is large, underlining the necessity of more realistic models.
We focus here on the large-scale Inverse Compton (IC) component...
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 structures within the bubbles. One prominent region, the cocoon, has recently been associated with gamma-ray emissions from the Sagittarius dwarf...
We estimated the contribution from clusters of galaxies to the diffuse neutrino and $\gamma-$ray background. Due to their unique magnetic-field configuration, CRs with energy $\leq10^{17}$ eV can be confined within these structures over cosmological time scales, and generate secondary particles, including neutrinos and gamma-rays, through interactions with the background gas and photons. We...
Particle physics is at a crossroads: new physics is there, but we do not know where to search for it. Astrophysics and cosmology offer many opportunities to reduce the parameter space for new physics. In this talk, I will focus on a potential relic that could bring us invaluable information about processes in the early universe and, thus, about new physics. Strong hints from gamma-ray...
The binary system is an idea astrophysical laboratory to test physical laws at very extreme environment. With the improvement of sensitivity for gamma ray telescopes, gamma ray signals from high mass binary systems have also been detected. However, the detection of gamma rays from binary system is difficult due to the low flux and instability of signal, and the mechanism for emission is under...
A robust spectrum of gamma-ray emissions from solar disk reaches up to 200 GeV with no cutoff has been reported with Fermi-LAT. Recent results from HAWC also extended the energy up to 1 TeV. Many startling mysteries and open questions have shown up along with the unknown mechanism to understand its spectrum, time variability, and morphology. Any significant observation signals or a strong...
Despite its very close proximity to Earth, there are still many unsolved puzzles about the Sun. One such example of significant recent interest relates to the gamma-ray emission (in the GeV-TeV range) from the solar disk. A major contribution to the solar emission in this energy range is believed to be caused by the interaction of galactic cosmic rays (GCRs) with the solar atmosphere: the...
The Sun emits gamma rays ranging from several hundred MeV to 1 TeV through hadronic cosmic ray interactions with the solar atmosphere. A critical factor influencing this phenomenon is the reflection of cosmic rays by solar magnetic fields in the photosphere and the upper convection zone. In this talk, I will present a simplified solar magnetic flux tube structure that combines network elements...
In this contribution, we present the latest updates introduced to agnpy - an open-source python package for modeling broadband spectra of blazars.
Among the significant updates, we discuss the implementation of hadronic radiative processes. The agnpy software now implements proton synchrotron radiation and we are working also to implement the photohadronic process. Additionally, we...
We will given an overview of recent developments in numerical modelling of cosmic-ray transport and ensuing gamma-ray emission within our Galaxy using the Picard code. Picard is a cosmic-ray propagation code allowing for efficient solution of spatially three-dimensional models. We will discuss challenges at arriving at the necessary three-dimensional models of our Galaxy that determine the...
About one third of the Fermi-LAT sources have no high probability associations. Some of the sources may have no observable counterparts at other frequencies, such as pulsars with misaligned radio jets. For these sources probabilistic classification, e.g., with machine learning (ML), may be the only possibility to understand their nature. One of the main problems in using ML for classification...
The IceCube Neutrino Observatory is situated at the geographic South Pole. IceCube is composed of two detectors. One is an in-ice optical array that is sensitive to high-energy muons from air showers as well as particle cascades that are induced by high-energy neutrino interactions in the ice. The other detector, called IceTop, is an array of ice-cherenkov tanks on the surface above the in-ice...
We started a new air shower observation experiment, ALPACA, to observe cosmic gamma rays and cosmic rays of several TeV or more from the southern sky of the galaxy.
The ALPACA’s location is at an altitude of 4,740 m on the hillside in Chacaltaya, Bolivia,
The ALPACA consists of a ground-based air shower detector array of 401 scintillation detectors and a large-area water Cherenkov-type...
The Southern Wide-field Gamma-ray Observatory (SWGO), currently in the R&D phase, is the project to design and build the first wide-field ground-based observatory in the Southern hemisphere, for the detection of gamma-rays from a few hundred GeV to a few PeV. The extensive air shower array, planned for deployment at an altitude greater than 4400 m a.s.l., will be primarily based on water...
The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel concept for a next-generation telescope covering the MeV band. We will present the potential and importance of this approach that bridges the observational gap between the keV and GeV energy range. With the unprecedented angular resolution of the coded-mask telescope combined with the sensitive Compton...
The Compton Spectrometer and Imager (COSI) is a Small Explorer satellite mission selected by NASA and scheduled to launch in 2027. COSI employs a novel Compton telescope consisting of a compact array of cross-strip germanium detectors. Owing to its wide field-of-view and excellent energy resolution, COSI will achieve an unprecedented sensitivity in the MeV range, especially for gamma-ray...
