Related papers: A method for localizing energy dissipation in blaz…
We present results of variability study of a sample of 20 powerful blazars using Fermi/LAT (0.1--300 GeV) observations. We studied decade-long observations applying various analysis tools such as flux distribution, symmetry analysis, and…
Context. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components, spatially indistinguishable by gamma-ray instruments, but separated by a…
Fermi-LAT analyses show that the gamma-ray photon spectral indices Gamma_gamma of a large sample of blazars correlate with the vFv peak synchrotron frequency v_s according to the relation Gamma_gamma = d - k log v_s. The same function, with…
Rapid variability of the TeV emission in several blazars implies a central black hole mass $M_{BH}<10^8M_\odot$, appreciably smaller than the values estimated from the $M_{BH}-L_{bulg}$ relation, and Doppler factors for the $\gamma$-ray…
In external Compton scenario, we investigate the formation of the very hard electron spectrum in the fast-cooling regime, using a time-dependent emission model. It is shown that a very hard electron distribution $N'_{\rm…
Several high-frequency peaked BL Lac objects such as Mrk 501 are strong TeV emitters. However, a significant fraction of the TeV gamma rays emitted are likely to be absorbed in interactions with the diffuse IR background, yielding…
The currently developing space-based gamma-ray telescope GAMMA-400 will measure the gamma-ray and electron + positron fluxes using the main top-down aperture in the energy range from ~20 MeV to several TeV in a highly elliptic orbit…
The prompt GRB emission is thought to arise from electrons accelerated in internal shocks propagating within a highly relativistic outflow. The launch of Fermi offers the prospect of observations with unprecedented sensitivity in…
We examine the constraints on the luminosity-dependent density evolution model for the evolution of blazars given the observed spectrum of the diffuse gamma-ray background (DGRB), blazar source-count distribution, and the blazar spectral…
Context. Blazar flares provide a window into the extreme physical processes occurring in relativistic outflows. Most numerical codes used for modeling blazar emission during flares utilize a simplified continuous-loss description of…
Blazars are a sub-category of radio-loud active galactic nuclei with relativistic jets pointing towards the observer. They exhibit non-thermal variable emission, which practically extends over the whole electromagnetic spectrum. Despite the…
Models of quantum gravity suggest that the vacuum should be regarded as a medium with quantum structure that may have non-trivial effects on photon propagation, including the violation of Lorentz invariance. Fermi Large Area Telescope (LAT)…
Recent detections of GeV photons in a few GRBs by Fermi-LAT imply huge bulk Lorentz factors to avoid a large gamma gamma optical depth at high energy. Estimates can be as high as Gamma ~ 1000 in the most extreme cases. This puts severe…
High-energy gamma-ray emission from the Galactic plane above ~100 MeV is composed of three main contributions: diffuse emission from cosmic ray interactions in the interstellar medium, emission from extended sources, such as supernova…
The physics-determined broadband spectral energy distributions (SEDs) of blazars have been widely used to study the property during their flaring/outburst states, while the non-flaring state takes up most of their lifetime and the general…
Observations of very-high-energy (VHE, E > 250 GeV) gamma-ray emission from several blazars at z > 0.1 have placed stringent constraints on the elusive spectrum and intensity of the intergalactic infrared background radiation (IIBR).…
Radially inhomogeneous gamma-ray burst (GRB) jets release variable photospheric emission and can have internal shocks occurring above the photosphere. We generically formulate a photospheric emission model of GRBs including Compton…
We present total and linearly polarized 3 mm Global mm-VLBI Array images of a sample of blazars and radio galaxies from the VLBA-BU-BLAZAR 7 mm monitoring program designed to probe the innermost regions of active galactic nuclei (AGN) jets…
With their emission mainly coming from a relativistic jet pointing towards us, blazars are fundamental sources to study extragalactic jets and their central engines, consisting of supermassive black holes (SMBHs) fed by accretion discs.…
Since 2002, the number of detected blazars at gamma-ray energies above 100 GeV has more than doubled. I study 17 blazars currently known to emit E>100 GeV gamma rays. Their intrinsic energy spectra are reconstructed by removing…