Related papers: Correlations between X-ray spectral parameters of …

Short-term variability of X-ray continuum spectra has been reported for several Active Galactic Nuclei. Significant X-ray flux variations are observed within time scales down to 10^3-10^5 seconds. We discuss short variability time scales in…

We study the behaviour of the cyclotron resonant scattering feature (CRSF) of the high mass X-ray binary Vela X-1 using the long-term hard X-ray monitoring performed by the Burst Alert Telescope (BAT) on board Swift. High statistics,…

X-ray flares are generally supposed to be produced by the later central engine activities, and may share the similar physical origin with prompt emission of gamma-ray bursts (GRBs). In this paper, we have analyzed all significant X-ray…

We present the 0.5 - 78 keV spectral analysis of 18 broad line AGN belonging to the INTEGRAL complete sample. Using simultaneous Swift-XRT and NuSTAR observations and employing a simple phenomenological model to fit the data, we measure…

We present a detailed study of the spectral and temporal properties of the X-ray flares emission of several GRBs. We select a sample of GRBs which X-ray light curve exhibits large amplitude variations with several rebrightenings superposed…

We examine the long term (~10 years) gamma-ray variability of blazars observed by EGRET and Fermi and find that for six sources the average flux varied by more than an order of magnitude. For two of these sources (PKS 0208-512 and PKS…

As one of the most active blazars, Mrk421 is an excellent candidate for the study of the physical processes within the jets of AGN. Here we report on the extensive multi-wavelength observations of Mrk 421 over 4.5 years, from 2008 August to…

We study simultaneous soft ($0.7 - 7$ keV) and hard ($7 - 20$ keV) X-ray light curves at a total of eight epochs during $2016 - 2019$ of two TeV blazars Mrk 421 and 1ES 1959+650 observed by the SXT and LAXPC instruments onboard AstroSat.…

We present optical, X-ray, high energy ($\lessapprox 30$ GeV) and very high energy ($\gtrapprox 100$ GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high energy $\gamma$-ray signal…

We consider particle acceleration to high energy via diffusive shock acceleration in a simple, self-consistent shock in jet model for blazars. Electrons are assumed to be accelerated at a shock front in relativistic jets and radiate…

During a period of strong $\gamma$-ray flaring activity from BL Lacertae, we organized Swift, Neutron star Interior Composition Explorer (NICER), and Nuclear Spectroscopic Telescope Array (NuSTAR) follow-up observations. The source has been…

Blazars are a subclass of active galactic nuclei (AGN) that have a relativistic jet with a small viewing angle towards the observer. Recent results based on hadronic scenarios have motivated an ongoing discussion of how a blazar can produce…

We are performing an unprecedentedly long and dense monitoring of the multi-frequency (radio to TeV) emission from the classical TeV blazars Mkn 421 and Mkn 501. These objects are among the brightest X-ray/TeV blazars in the sky and among…

Blazars are highly variable, radio-loud active galactic nuclei with jets oriented at a small angle to the line of sight. The observed emission of these sources covers the whole electromagnetic spectrum from radio frequencies up to the high…

Short-term variability of X-ray spectra has been reported for several Active Galactic Nuclei. Significant X-ray flux variations are observed within time scales down to 10^4 -- 10^5 seconds. We discuss short variability time scales in the…

Context: The blazar Markarian 421 is one of the brightest TeV gamma-ray sources of the northern sky. From December 2007 until June 2008 it was intensively observed in the very high energy (VHE, E > 100 GeV) band by the single-dish Major…

A detailed study of the BL Lacertae PKS 0903-57 has been done for the first time with 12 years of Fermi Large Area Telescope data. We have identified two bright gamma-ray flares in 2018 and 2020. Many sub-structures were observed during…

We present X-ray spectra ($0.7-20$ keV) of two high synchrotron-peaked blazars Mrk 421 and 1ES 1959+650 from simultaneous observations by the SXT and LAXPC instruments onboard \textit{AstroSat} and the \textit{Swift}-XRT during multiple…

The nature of fast radio bursts (FRBs) is currently unknown. Repeating FRBs offer better opportunity than non-repeating FRBs since their simultaneous multi-wavelength counterparts might be identified. The magnetar flare model of FRBs is one…

We have been using the 0.76-m Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory to optically monitor a sample of 157 blazars that are bright in gamma rays, being detected with high significance ($\ge 10\sigma$) in one year by…