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