In 2015 the advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO) detected the first ever gravitational event, gravitational wave event GW150914, with multiple new gravitational wave events, originating from both binary neutron stars and binary black hole (BBH) mergers, detected in subsequent years. In light of these detections, we simulate the dynamics of ambient test particles...
We present the results of a detailed investigation of the prompt and afterglow emission in the High Energy Stereoscopic System(H.E.S.S.)-detected GRB190829A. Swift and Fermi observations of the prompt phase of this gamma-ray burst(GRB) reveal two isolated sub bursts or episodes, separated by a quiescent phase. The energetic and the spectral properties of the first episode are in stark contrast...
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...
Blazars are extremely variable sources showing flux variations on time scales from minutes to years. To study typical variability time scales of few hours to one day, continuous observations are crucial. Furthermore, studying the temporal evolution of the spectral energy distribution is a key to discriminate between different theoretical models for the emission mechanisms and processes...
I will present the interesting case of GRB 190114C, the first GRB ever detected by MAGIC at Very High Energy (VHE). We analyzed the spectral evolution of its gamma-ray emission as detected by the Fermi Gamma-Ray Burst Monitor (GBM) up to∼60 s. We revealed the presence of an extra component starting on ∼4 s post-trigger. This extra component rises and decays quickly (peaking at∼6 s) and it is...
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...
GRB 171205A was one of the closest GRBs that we have ever detected and one of the best-followed events. In this talk I will present the result of several studies of this event, its afterglow, associated supernova SN2017iuk, and host galaxy. Optical spectroscopy ranges from one hour after the event to more than 7 months later. These data served to identify cocoon signatures during the first 3...
Two classes of gamma-ray bursts (GRBs), short and long, have been confidently identified thus far and are prescribed to different physical scenarios. A third class, intermediate in duration, was suggested to be present in various catalogues based on a mixture-modelling with two or three Gaussian distributions of the log-durations, log(T90). This might not be an adequate model. An analysis of...
The second Fermi LAT GRB catalog presents the results for 186 Gamma Ray Bursts (GRBs) detected by the Fermi Large Area Telescope (LAT) between 2008 and 2018. Out of these, we select the GRBs with significant detection in the LAT and GBM during the T90 time interval. We further subdivide this population into four quartiles based on the fluence from the GBM and carry out joint GBM-LAT spectral...
TeV emissions from Gamma-ray bursts (GRBs) are very important to study the origin and the radiation mechanisms in detail. Recent discoveries of TeV photons in some of the GRBs are challenging to be explained by Synchrotron mechanism. In this work, we present the results of a detailed investigation of the prompt and afterglow emission of recently discovered TeV GRBs (GRB 180720B, GRB 190114C...
For research, our group uses an installation with an area of 55 m2, consisting of two recording levels, gamma and hadron blocks, separated by a two-meter gap, located at the Tien Shan high-altitude scientific station. The main idea is to select interactions that are only observed in the gamma block, and not observed in the hadron block.
The upgraded ionization calorimeter with a field of...
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...
Operational since October 2011, the First G-APD Cherenkov Telescope
(FACT) has been monitoring TeV-blazars. An unbiased observing strategy,
robotic operation and the usage of solid state photo sensors (SiPM, aka
G-APDs) increase the instrument's duty cycle and minimize observational
gaps, making FACT an ideal instrument for long-term monitoring. In more
than eight years, an unprecedented...
We perform three-dimensional (3D) general-relativistic magnetohydrodynamic sim-
ulations to model the jet break-out from the ejecta expected to be produced in a
binary neutron-star merger. The structure of the relativistic outflow from the 3D sim-
ulation confirms our previous results from 2D simulations, namely, that a relativistic
magnetized outflow breaking out from the merger ejecta...
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...
We present the observations of the first unambiguous magnetar giant flare from outside of our galactic neighborhood. At the beginning, GRB 200415A was identified as a short GRB, but upon further investigation and observations from additional instruments, we concluded this event was a giant flare from a magnetar located in the Sculptor galaxy, 3.5 Mpc away. The GBM lightcurve shows very fast...
The nature of the gamma-ray burst (GRB) central engine remains an enigma. Entities widely considered to be capable of powering the extreme jets are: (i) a hyper-accreting stellar-mass black hole, and (ii) a rapidly spinning, highly magnetized, neutron star (NS) or fast magnetar. The maximum rotational energy that is feasible in a millisecond magnetar to form a jet is ~10^52 erg and hence...
