Related papers: A hadronic emission model for black hole-disc impa…
Monitoring of the narrow line Seyfert 1 galaxy Markarian 335 (Mrk 335) with the Swift satellite discovered an X-ray flare beginning 2014 August 29. At the peak, the 0.5-5keV count rate had increased from that in the low flux state by a…
We describe a set of simulations of super-critical accretion onto a non-rotating supermassive BH. The accretion flow is radiation pressure dominated and takes the form of a geometrically thick disk with twin low-density funnels around the…
An electron-positron cascade in the magnetospheres of Kerr Black Holes (BH) is a fundamental ingredient to fueling the relativistic $\gamma$-ray jets seen at the polar regions of galactic supermassive BHs (SMBH). This leptonic cascade…
We propose that TeV $\gamma$-ray emission from blazars is produced by collisions near the line of sight of high energy jet protons with gas targets (``clouds'') from the broad emission-line region (BLR). Intense TeV $\gamma$-ray flares…
Active galactic nuclei (AGNs) have been proposed as plausible sites for hosting a sizable fraction of the binary black hole (BBH) mergers measured through gravitational waves (GWs) by the LIGO-Virgo-Kagra (LVK) experiment. These GWs could…
Supermassive black hole binaries (SMBHBs) are natural by-products of galaxy mergers and are expected to be powerful multi-messenger sources. They can be powered by the accretion of matter and then radiate across the electromagnetic…
The blazar 3C 279 exhibited twin $\gamma$-ray flares of similar intensity in 2013 December and 2014 April. In this work, we present a detailed multi-wavelength analysis of the 2013 December flaring event. Multi-frequency observations reveal…
Sgr A*, the compact radio source, believed to be the counterpart of the massive black hole at the galactic nucleus, was observed to undergo rapid and intense flaring activity in X-rays with Chandra in October 2000. We report here the…
The spectral and temporal evolution during X-ray outbursts give important clues on the accretion process and radiation mechanism in black-hole X-ray binaries (BH XRBs). A set of Swift and RXTE observations were executed to monitor the 2008…
The physical mechanisms responsible for production of the non-thermal emission in accreting black holes (BH) should be imprinted in the observational apperances of the power law tails in the X-ray spectra from these objects. Different…
The detections of some long gamma-ray bursts (LGRBs) relevant to mergers of neutron star (NS)-NS or black hole (BH)-NS, as well as some short gamma-ray bursts (SGRBs) probably produced by collapsars, muddle the boundary of two categories of…
Flares from the supermassive black hole in our Galaxy, Sagittarius~A$^\star$ (Sgr A$^\star$), are routinely observed over the last decade or so. Despite numerous observational and theoretical efforts, the nature of such flares still remains…
Self-lensing flares (SLFs) are expected to be produced once or twice per orbit by an accreting massive black hole binary (MBHB), if the eclipsing MBHBs are observed close to edge-on. SLFs can provide valuable electromagnetic (EM) signatures…
Context. The blazar OJ 287 has been proposed as a binary black hole system based on its periodic optical outburst. Among blazars with parsec scale jets, the black hole binary systems are very rare and hence this source is very interesting…
Recent months have witnessed dramatic progress in our understanding of SGRBs. There is now general agreement that SGRBs can produce directed outflows of relativistic matter with a kinetic luminosity exceeding by many millions that of AGN.…
Observational signatures of accretion disc winds have been found in a significant number of low-mass X-ray binaries at either X-ray or optical wavelengths. The 2015 outburst of the black hole transient V404 Cygni provided a unique…
We employ a low angular momentum accretion-outflow scenario to model the flares emanating out from the central region of Sgr A$^*$. The primary donor for matter accreting onto the central SMBH of Sgr A$^*$ is assumed to be the WR star ISR…
We have recently proposed that supercritical colliding wind binaries (SCWBs) are suitable scenarios for particle acceleration and nonthermal radiation. In these X-ray binary systems (XRBs), the wind from the companion star collides with the…
We present a suite of the first 3D GRMHD collapsar simulations, which extend from the self-consistent jet launching by an accreting Kerr black hole (BH) to the breakout from the star. We identify three types of outflows, depending on the…
Black hole (BH) accretion disks are often coupled to ultramagnetized and tenuous plasma coronae close to their central BHs. The coronal magnetic field can exchange energy between the disk and the BH, power X-ray emission, and lead to jetted…