Related papers: AGN's UV and X-ray luminosities in clumpy accretio…
It is established that the ultraviolet (UV) and X-ray emissions in active galactic nuclei (AGN) are tightly correlated. This correlation is observed both in low- and high-redshift sources. In particular, observations of large samples of…
It is commonly believed that the optical/UV and X-ray emissions in luminous AGN are produced in an accretion disk and an embedded hot corona respectively. The inverse Compton scattering of disk photons by hot electrons in the corona can…
Within the standard accretion disk theory for active galactic nuclei (AGN), the observed X-rays are often modeled by Compton up-scattering of ultraviolet (UV) disk photons inside a hot disk corona. Here, we point out that for many AGN,…
We discuss accretion flows on massive black holes in which different elements of the flow (clumps) have velocities that may differ substantially. We estimate the consequence of collisions between these clumps as they come close to the…
The UV/optical and X-ray variability of active galactic nuclei (AGN) have long been expected to be well correlated as a result of the X-ray illumination of the accretion disk. Recent monitoring campaigns of nearby AGN, however, found that…
To provide insight into the apparent mismatch between the optical and X-ray absorption properties observed in 10-30 % of Active Galactic Nuclei (AGN), we have conducted a detailed study of two X-ray unabsorbed AGN with a type-2 optical…
We report that moderately eccentric flows around supermassive black holes (SMBHs), formed via either circumnuclear gas accretion or tidal disruption events, generate eccentricity cascades (from >0.8 to 0.2 outward), explaining…
We propose that the X--ray emission from radio quiet AGN and galactic black holes is due to Comptonization of soft thermal photons emitted by the underlying accretion disk in localized structures (blobs). The power per unit area produced by…
Accretion flows toward black holes can be of a quite different nature, described as an optically thick cool gas flow in a disk for high accretion rates or as a hot coronal optically thin gas flow for low accretion rates, possibly affected…
More than half of all low-redshift AGN exhibit UV and X-ray absorption by highly ionized gas. The observed UV and X-ray absorption lines are almost always blue-shifted at velocities of hundreds of km/s, indicating that the absorbing gas is…
By comparing the ratio of flux densities in the X-ray and UV wavebands by way of the spectral optical-X-Ray index, $\alpha_{ox}$, we explore the relation between the emissions in the respective wavebands for a number of ULXs with known…
The discovery of changing-look active galactic nuclei (CL AGNs), with appearance and disappearance of broad emission lines and/or with strong variation of line-of-sight column density within a few years, challenges the AGN unification…
We study the relation of optical/UV and X-ray emission in the low luminosity active galactic nuclei (LLAGNs), using a sample of 49 sources including 28 local Seyfert galaxies and 21 low-ionization nuclear emission-line regions (LINERs) with…
Active Galactic Nuclei (AGN) are believed to be powered by accretion of matter onto a supermassive black hole. A fundamental ingredient in shaping our understanding of AGN is their variability across the entire electromagnetic spectrum.…
We investigate the observed correlation between the 2--10 keV X-ray luminosity (in unit of the Eddington luminosity; $l_X \equiv L_X/L_{Edd}$) and the photon index ($\Gamma$) of the X-ray spectrum for both black hole X-ray binaries (BHBs)…
Observed spectra of Active Galactic Nuclei (AGN) and luminous X-ray binaries in our Galaxy suggest that both hot (~10^9 K) and cold (~10^6 K) plasma components exist close to the central accreting black hole. Hard X-ray component of the…
The luminous electromagnetic emission from distant active galactic nuclei (AGNs) including quasars is believed to be powered by accretion onto super-massive black holes (SMBHs). In the standard unification model for AGNs a dusty torus…
Despite their factor of ~10^8 difference in black hole mass, several lines of evidence suggest possible similarities between black hole accretion flows in active galactic nuclei (AGN) and Galactic X-ray binaries. However, it is still…
The physical origin of optical changing-look AGNs (CLAGNs), characterized by the appearance or disappearance of broad emission lines, is thought to be mainly driven by the variation of the black-hole (BH) accretion rate. In this work, we…
Radiation emitted from an accretion disk around a massive black hole is a widely discussed model for the UV/soft X-ray excess emission observed in the spectra of many AGN. A self-consistent calculation of the structure and the emerging…