The upper limits from the Milky Way (MW) dwarf spheroidal galaxies remain one of the most important constraints on dark matter (DM) annihilation, and specifically, they are crucial for DM interpretations of the Galactic center excess. The last detailed analysis by the Fermi-LAT Collaboration dedicated to studying the dwarfs was published in 2017, using roughly 6 years of data. Now, with over...
ΛCDM predicts the existence of dark matter (DM) subhalos, most of them not massive enough to retain gas (i.e., baryons) and become visible. If DM is composed of Weakly Interacting Massive Particles (WIMPs), we expect them to annihilate in subhalos, producing gamma rays which can be detected with the Large Area Telescope (LAT) onboard the Fermi satellite, and appearing as unidentified sources...
Microquasars, the local siblings of extragalactic quasars, are binary systems comprising a compact object and a companion star. By accreting matter from their companions, microquasars launch powerful winds and jets, influencing the interstellar environment around them. Steady gamma-ray emission is expected to rise from their central objects, or from interactions between their outflows and the...
Gamma-ray binaries are a small but growing class of sources which comprises of binary systems where the spectral energy distribution peaks above 1 MeV. Gamma-ray photons emitted in binary systems are subject to gamma-gamma absorption as they travel through a photon field created by a massive star. Moreover, gamma-gamma absorption might be the main reason for the characteristic decrease of the...
Dark matter particles in the Galactic halo could interact with the nuclei in the solar environment and be then gravitationally trapped by the Sun. In this framework, the overdensity of dark matter particles in the Sun core or in external orbits will result in annihilations of these particles producing gamma rays outside the Sun, either directly or via long-lived intermediate states.
We...
The Fermi LAT Fourth Source Catalog (4FGL) contains over 5000 gamma-ray sources detected using 8 years of LAT data. Among these sources, over 3000 are associated with known blazars, 239 are associated with pulsars, and over 1300 are classified as 'unassociated' sources, meaning they have no known plausible counterpart at any other wavelength. Following on our previous work on the 3FGL Catalog...
QSO B0218+357 is currently the only gravitationally lensed source from which both high-energy (HE, >~100 MeV) and very-high-energy (VHE,>~100GeV) gamma-ray emission has been detected.
We report the Fermi/LAT and multiwavelength monitoring observations of this source in radio interferometry, optical and X-rays performed between 2016 and 2020. During the monitoring, individual flares in the...
TeV DM candidates are gradually earning more and more attention within the community. Among others, extra-dimensional brane-world models may produce thermal DM candidates with masses up to 100 TeV, which could be detected with the next generation of very-high-energy gamma-ray observatories such as the Cherenkov Telescope Array (CTA).
In this work, we study the sensitivity of CTA to branon DM...
The flat-spectrum radio quasar QSO B1420+326 underwent an enhanced gamma-ray flux state seen by Fermi-LAT at the turn of 2019/2020. Compared to the low state both the position and luminosity of the two spectral energy distribution peaks changed by at least two orders of magnitude. The high state resulted in the discovery of the very-high-energy (>100 GeV) gamma-ray emission from the source by...
An accurate estimate of the interstellar gas density distribution is crucial to understanding the interstellar medium (ISM) and Galactic cosmic rays (CRs). However, a significant amount of gas not traced properly by standard radio line surveys (``dark gas") has been preventing accurate measurement of the total neutral gas column density and CR intensity. To overcome this difficulty, we...
In recent work, we have developed a self consistent two-zone model of
time-dependent diffusive shock acceleration in the relativistic jets of
blazars and the resulting multi-wavelength spectral and variability
features. In this paper, we report the results of detailed fitting of
this model to recent multi-wavelength data from two blazars detected
during bright gamma-ray flares by...
The Large Area Telescope onboard the Fermi Gamma-ray Space Telescope has collected more than 15 millions of cosmic-ray electron and positron (CRE) events in the energy range from 42 GeV to 2 TeV in about 7.5 years since its launch in 2008. We have searched for possible features in the energy spectrum of Galactic CREs, which could be interpreted as a signature of the presence of a nearby dark...
Despite the enormous efforts done in very recent years, both theoretically and experimentally, the basic three questions about the CR origin remain without clear answers: what are their sources, how are they accelerated, how do they propagate?
Gamma-ray astronomy plays a fundamental role in this field. Both relativistic protons and electrons can emit in the gamma-ray band with different...
Fast radio bursts (FRBs) are millisecond-duration radio flashes of unknown physical origin. We now know that they originate at cosmological distances and hence must be exceptionally luminous. As such, FRBs promise to provide a new view of extreme astrophysics in action. At the same time, FRBs also promise to be unique probes of the ionised material within and between galaxies. Though only...
PSR J2021+4026 in the Cygnus region is one of the most interesting radio-quiet pulsars detected by Fermi-LAT. This source, thought to be associated with the Gamma Cygni supernova remnant, is the first isolated gamma-ray pulsar that exhibited clear evidence of variability, with a simultaneous flux and spindown change first occurred in October 2011. After a long recovery phase, in August 2015...
γ-ray bursts (GRBs) are cataclysmic events, whose role became central in the new multi-messenger era. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. In the present work I propose a novel investigation of the GRB emission mechanism, via time-resolved...
Over the past few years, evidence has been accumulated in support of the existence of a thermal-like component during the GRB prompt phase. This component--often associated with the GRB jet's photosphere--is usually subdominant compared to a much stronger non-thermal one. The prompt emission of GRB 131014A detected by Fermi provides a unique opportunity to trace the history of this...
Short gamma-ray burst are, as we now know, produced as the result of the coalescence of two compact objects. These objects are also known to release large amounts of energy in gravitational waves during the merger. We present our first results on the study of GRB 160410A, an undoubtedly short GRB at z=1.717, making it one of the farthest short GRBs to date. We observed the afterglow emission...
The gamma-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 components: a stellar disk emission, where gamma-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...
The Cherenkov Telescope Array (CTA) will be the next generation very high-energy (VHE) gamma-ray observatory. It will improve the sensitivity of current VHE instruments up to an order of magnitude and will cover the energy range from 20 GeV to at least 300 TeV. With its sensitivity, it will explore high redshift sources and extreme accelerators and will give access to the shortest timescale...
Supernova remnants (SNRs) are widely believed to be one of the main candidates for the origin of Galactic cosmic rays. Very-high-energy gamma-ray emission observed from a number of SNRs suggests that particles are indeed accelerated to high energies by shock in remnants. However, it is extremely difficult to discriminate which particles are responsible for this emission as both protons...
On January 14th 2019, MAGIC, a stereoscopic system of two 17m diameter Imaging Atmospheric Cherenkov Telescopes located on the Canary island of La Palma, observed for the first time a gamma-ray burst (GRB) at TeV energies, namely GRB 190114C. MAGIC measurements started ~60s after the onset of GRB 190114C, predominantly in the featureless smooth afterglow phase. Nevertheless, in the first 30s...
The Fermi data imply that the gamma-ray observables, i.e., the gamma-ray luminosity, spectral cut-off energy, stellar surface magnetic field, and spin-down power obey a relation that represents a 3D plane in the 4D log-space. This observed fundamental plane (FP) is remarkably close to the theoretical relation that is obtained, assuming that the pulsar gamma-ray emission is due to curvature...
The Cherenkov Telescope Array (CTA) will be the next generation very high-energy (VHE) gamma-ray observatory. It will improve the sensitivity of current VHE instruments up to an order of magnitude and will cover the energy range from 20 GeV to at least 300 TeV. With its sensitivity, it will explore high redshift sources and extreme accelerators and will give access to the shortest timescale...
γ-ray bursts (GRBs) are cataclysmic events, whose role became central in the new multi-messenger era. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. In the present work I propose a novel investigation of the GRB emission mechanism, via time-resolved...
TeV DM candidates are gradually earning more and more attention within the community. Among others, extra-dimensional brane-world models may produce thermal DM candidates with masses up to 100 TeV, which could be detected with the next generation of very-high-energy gamma-ray observatories such as the Cherenkov Telescope Array (CTA).
In this work, we study the sensitivity of CTA to branon DM...
On January 14th 2019, MAGIC, a stereoscopic system of two 17m diameter Imaging Atmospheric Cherenkov Telescopes located on the Canary island of La Palma, observed for the first time a gamma-ray burst (GRB) at TeV energies, namely GRB 190114C. MAGIC measurements started ~60s after the onset of GRB 190114C, predominantly in the featureless smooth afterglow phase. Nevertheless, in the first 30s...
Over the past few years, evidence has been accumulated in support of the existence of a thermal-like component during the GRB prompt phase. This component--often associated with the GRB jet's photosphere--is usually subdominant compared to a much stronger non-thermal one. The prompt emission of GRB 131014A detected by Fermi provides a unique opportunity to trace the history of this...
The Fermi LAT Fourth Source Catalog (4FGL) contains over 5000 gamma-ray sources detected using 8 years of LAT data. Among these sources, over 3000 are associated with known blazars, 239 are associated with pulsars, and over 1300 are classified as 'unassociated' sources, meaning they have no known plausible counterpart at any other wavelength. Following on our previous work on the 3FGL Catalog...
Short gamma-ray burst are, as we now know, produced as the result of the coalescence of two compact objects. These objects are also known to release large amounts of energy in gravitational waves during the merger. We present our first results on the study of GRB 160410A, an undoubtedly short GRB at z=1.717, making it one of the farthest short GRBs to date. We observed the afterglow emission...
The IceCube neutrino observatory at the geographic South Pole has been operating at full capacity for the past ten years. In 2013, IceCube reported first evidence of an isotropic flux of astrophysical neutrinos in the TeV-PeV energy range. While the flux is by now observed with high significance, its astrophysical origin is unknown. Only recently, IceCube was able to report first compelling...
Multi-messenger astrophysics experienced a tremendous boost, after the first detection of astrophysical neutrinos was reported eight years ago. Despite having uncovered a large variety of gamma-ray emitting source classes up to today, a firm identification of the dominant source population responsible for the detected high-energy neutrino all-sky flux is, however, still lacking.
In this...
With the completion of the first decade of operation, Fermi-GBM has been longer in orbit than its predecessor experiment BATSE on-board CGRO. It is capable to detect almost the same number of GRBs (~240 GBM GRBs compared ~300 BATSE GRBs per year) resulting in 2357 triggers on cosmic GRBs during the first ten years. The GBM GRB catalog series is now continued by the latest releases of the GBM...
The simultaneous detection of a high energy neutrino event during a gamma-ray flare from TXS 0506+056 played an essential role in its identification as an astrophysical neutrino source in 2017. This highlights the current importance of electromagnetic follow-up by gamma-ray instruments for finding new sources in the field of high-energy neutrino astronomy where many of the sources and source...
Cosmic rays are mostly composed by protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions which in turn decay into gamma rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum was detected in the gamma-ray spectra of four Supernovae Remnants (SNRs), IC 443, W44,...
The Fermi Flare Advocate (also known as Gamma-ray Sky Watcher, FA-GSW) service provides for a quick look and review of the gamma-ray sky observed daily by the Fermi Large Area Telescope (LAT) through on-duty LAT Flare Advocates and high level software pipelines like the LAT Automatic Science Processing (ASP), the Fermi All-sky Variability Analysis (FAVA), a dedicated suite of software and,...
Supernova Remnants (SNRs) emitting gamma rays in the GeV-TeV energy range are fundamental for identifying the accelerators of Galactic cosmic rays. In 2018 H.E.S.S. has revealed at TeV energies three extended shell-like sources: HESS J1534-571, HESS J1614-518 and HESS J1912+101. A radio Supernova Remnant (SNR) candidate has been identified as a counterpart to HESS J1534-571, therefore it is...
VERITAS, an array of atmospheric-Cherenkov telescopes sensitive to gamma rays in the very-high-energy range (VHE, E > 100 GeV), carries out an extensive multimessenger program focused on the search for electromagnetic counterparts to high-energy neutrinos and gravitational waves. As both neutrinos and gamma rays are expected to be produced in hadronic interactions near cosmic ray accelerators,...
Blazars can show variability on a wide range of timescales. However, the search for periodicity in the gamma-ray emission of blazars remains an on-going challenge. This contribution will show the results obtained when a systematic pipeline is used to implement ten well-established methods for searching for periodicity. We analyze the most promising candidates selected from our previous work,...
We report on the observations by Fermi and Swift of gamma-ray burst (GRB) 190114C detected at very high energy by MAGIC. The prompt gamma-ray emission was detected by the Fermi/GBM, the Fermi/LAT, and the Swift/BAT and the long-lived afterglow emission was subsequently observed by the GBM, LAT, Swift/XRT, and Swift/UVOT. The early-time observations reveal multiple emission components that...
The Fermi Large Area Telescope (LAT) has detected ~250 gamma-ray pulsars in its > 10 years of operation. The gamma-ray emission from most of these pulsars peaks in the GeV range, where the LAT is most sensitive; perhaps not surprisingly, only a handful of them fall in the "soft" gamma-ray category. While Fermi pulsars are teaching us much about the pulsar mechanism, the full picture is still...
We report the modelling of the optical polarized emission of the white dwarf pulsar in the binary system AR Scorpii (AR Sco) in the framework of the striped pulsar wind model constrained by optical photopolarimetric data. One of the main goals of this work is to constrain the parameters, which describe the white dwarf pulsar magnetic field geometry. Besides, we determine the location of the...
Axion-like particles (ALPs) are hypothetical very light neutral spin-zero bosons predicted by superstring theory which can oscillate into photons in the presence of external magnetic fields. ALPs are attracting increasing interest in the high- and very-high-energy (VHE) astrophysics, since they can explain several issues: they mitigate Universe transparency at VHE, explain why flat spectrum...
The asteroid 1I/’Oumuamua (A/2017 U1) and the cometary-like object 2I/Borisov (C/2019 Q4) are the first two objects of interstellar origin discovered in our Solar system. They approached the Earth in October 2017 and in December 2019 respectively.
We searched for gamma-ray emission with the Fermi Large Area Telescope (LAT) data for energies above 56 MeV, focusing on the period before...
PSR J2021+4026 in the Cygnus region is one of the most interesting radio-quiet pulsars detected by Fermi-LAT. This source, thought to be associated with the Gamma Cygni supernova remnant, is the first isolated gamma-ray pulsar that exhibited clear evidence of variability, with a simultaneous flux and spindown change first occurred in October 2011. After a long recovery phase, in August 2015...
QSO B0218+357 is currently the only gravitationally lensed source from which both high-energy (HE, >~100 MeV) and very-high-energy (VHE,>~100GeV) gamma-ray emission has been detected.
We report the Fermi/LAT and multiwavelength monitoring observations of this source in radio interferometry, optical and X-rays performed between 2016 and 2020. During the monitoring, individual flares in the...
The gamma-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 components: a stellar disk emission, where gamma-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...
Supernova remnants (SNRs) are widely believed to be one of the main candidates for the origin of Galactic cosmic rays. Very-high-energy gamma-ray emission observed from a number of SNRs suggests that particles are indeed accelerated to high energies by shock in remnants. However, it is extremely difficult to discriminate which particles are responsible for this emission as both protons...
The Fermi data imply that the gamma-ray observables, i.e., the gamma-ray luminosity, spectral cut-off energy, stellar surface magnetic field, and spin-down power obey a relation that represents a 3D plane in the 4D log-space. This observed fundamental plane (FP) is remarkably close to the theoretical relation that is obtained, assuming that the pulsar gamma-ray emission is due to curvature...
PSR J2021+4026 in the Cygnus region is one of the most interesting radio-quiet pulsars detected by Fermi-LAT. This source, thought to be associated with the Gamma Cygni supernova remnant, is the first isolated gamma-ray pulsar that exhibited clear evidence of variability, with a simultaneous flux and spindown change first occurred in October 2011. After a long recovery phase, in August 2015...
The Cherenkov Telescope Array (CTA) will be the next generation very high-energy (VHE) gamma-ray observatory. It will improve the sensitivity of current VHE instruments up to an order of magnitude and will cover the energy range from 20 GeV to at least 300 TeV. With its sensitivity, it will explore high redshift sources and extreme accelerators and will give access to the shortest timescale...
The gamma-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 components: a stellar disk emission, where gamma-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...
γ-ray bursts (GRBs) are cataclysmic events, whose role became central in the new multi-messenger era. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. In the present work I propose a novel investigation of the GRB emission mechanism, via time-resolved...
On January 14th 2019, MAGIC, a stereoscopic system of two 17m diameter Imaging Atmospheric Cherenkov Telescopes located on the Canary island of La Palma, observed for the first time a gamma-ray burst (GRB) at TeV energies, namely GRB 190114C. MAGIC measurements started ~60s after the onset of GRB 190114C, predominantly in the featureless smooth afterglow phase. Nevertheless, in the first 30s...
Over the past few years, evidence has been accumulated in support of the existence of a thermal-like component during the GRB prompt phase. This component--often associated with the GRB jet's photosphere--is usually subdominant compared to a much stronger non-thermal one. The prompt emission of GRB 131014A detected by Fermi provides a unique opportunity to trace the history of this...
Supernova remnants (SNRs) are widely believed to be one of the main candidates for the origin of Galactic cosmic rays. Very-high-energy gamma-ray emission observed from a number of SNRs suggests that particles are indeed accelerated to high energies by shock in remnants. However, it is extremely difficult to discriminate which particles are responsible for this emission as both protons...
The Fermi data imply that the gamma-ray observables, i.e., the gamma-ray luminosity, spectral cut-off energy, stellar surface magnetic field, and spin-down power obey a relation that represents a 3D plane in the 4D log-space. This observed fundamental plane (FP) is remarkably close to the theoretical relation that is obtained, assuming that the pulsar gamma-ray emission is due to curvature...
Short gamma-ray burst are, as we now know, produced as the result of the coalescence of two compact objects. These objects are also known to release large amounts of energy in gravitational waves during the merger. We present our first results on the study of GRB 160410A, an undoubtedly short GRB at z=1.717, making it one of the farthest short GRBs to date. We observed the afterglow emission...
The High Energy Stereoscopic System (H.E.S.S.) has conducted a survey of the Milky Way, discovering 78 sources of very-high-energy (VHE, E > 100 GeV) gamma-ray emission. A total of 28 sources are firmly identified as being Pulsar Wind Nebulae (PWNe), Supernova Remnants (SNRs) or composite SNRs. Correlating the H.E.S.S. sources with other catalogues shows that 21 objects are firmly or plausibly...
The Fermi Large Area Telescope (LAT) has caused a revolution in the field of high-energy pulsar science. The number of known pulsars has sky-rocketed from a mere handful prior to its launch to more than 250, and the accumulation of statistics has yielded superior quality light curves in some cases. These developments have stimulated and enabled a flurry of theoretical activity, substantially...
The Cherenkov Telescope Array (CTA) is a next generation facility for ground-based gamma-ray astronomy operating in the very high energy (20 GeV to 300 TeV) range. It will consist of two telescope arrays, one on the island of La Palma in the Canary Islands, and the other near Paranal, Chile. CTA will provide order of magnitude improvements in sensitivity over current instrunments, together...
Astronomy plays a major role in the scientific landscape of Namibia and Southern Africa. Considerable progress has been achieved scientifically as well as in terms of human capacity development in the field. In all wavelength regimes accessible with ground-based instruments, the largest of those instruments are situated in Southern Africa: MeerKAT, the Southern African Large Telescope, and the...
TeV DM candidates are gradually earning more and more attention within the community. Among others, extra-dimensional brane-world models may produce thermal DM candidates with masses up to 100 TeV, which could be detected with the next generation of very-high-energy gamma-ray observatories such as the Cherenkov Telescope Array (CTA).
In this work, we study the sensitivity of CTA to branon DM...
QSO B0218+357 is currently the only gravitationally lensed source from which both high-energy (HE, >~100 MeV) and very-high-energy (VHE,>~100GeV) gamma-ray emission has been detected.
We report the Fermi/LAT and multiwavelength monitoring observations of this source in radio interferometry, optical and X-rays performed between 2016 and 2020. During the monitoring, individual flares in the...
The Fermi LAT Fourth Source Catalog (4FGL) contains over 5000 gamma-ray sources detected using 8 years of LAT data. Among these sources, over 3000 are associated with known blazars, 239 are associated with pulsars, and over 1300 are classified as 'unassociated' sources, meaning they have no known plausible counterpart at any other wavelength. Following on our previous work on the 3FGL Catalog...
At GeV energies, the sky is dominated by the interstellar emission from the Galaxy. With limited statistics and spatial resolution, accurate separation of point sources is therefore challenging. In this presentation I will describe the first application of deep learning based algorithms to detect and classify point sources from raw gamma-ray data. To detect point sources we utilise U-shaped...
Black widow (BW) and redback (RB) systems are compact binaries in which the pulsar heats or ablates its low-mass companion by its intense wind of relativistic particles and emission. Radio, optical and X-ray follow-up of unidentified Fermi Large Area Telescope (LAT) sources has expanded the number of these systems from four to nearly 30. Orbital modulation in X-rays suggests that in many...
Modeling of the NICER X-ray waveform of the pulsar PSR J0030+0451 aimed to constrain the neutron star mass and radius has inferred surface hot spots (i.e., the magnetic polar caps) that imply significantly non-dipolar magnetic fields. We investigate magnetic field configurations that comprise offset dipole plus quadrupole components using static vacuum field and force-free global magnetosphere...
We will present our follow-up studies of candidate TeV sources. Instead of a blind scan, we searched for significant multi-TeV emission from previously identified targets. Using data from the most recent HAWC sky map (1132 days), we followed up two lists of proposed sources: the sources flagged as good TeV candidates in the Third Catalog of Hard Fermi-LAT Sources (3FHL); and the unassociated...
The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space mission concept currently under Phase A study by ESA as candidate M5 mission, aiming at exploiting Gamma-Ray Bursts for investigating the early Universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. Through an unprecedented combination of X-/gamma-rays monitors, an...
The polarimetry of gamma rays converting to an e+e- pair would open a new window on the high-energy sky with, among other things, providing insight into the radiation mechanism in young pulsars (curvature or synchrotron) or deciphering the composition of the gamma-ray emitting jets in blazars (leptonic or lepto-hadronic).
The performance of polarimeters based on homogeneous active targets...
