Related papers: Accretion and emission processes in AGN
Rapid, large amplitude variability at optical to X-ray wavelengths is now seen in an increasing number of Seyfert galaxies and luminous quasars. The variations imply a global change in accretion power, but are too rapid to be communicated…
The disk corona evaporation model extensively developed for the interpretation of observational features of black hole X-ray binaries (BHXRBs) is applied to AGNs. Since the evaporation of gas in the disk can lead to its truncation for…
The central engines of active galactic nuclei (AGN) contain cold, dense material as well as hot X-ray emitting gas. The standard paradigm for the engine geometry is a cold thin disc sandwiched between hot X-ray coronae. Strong support for…
Popular models for the formation of X-ray spectra in AGN assume that a large fraction of the disk's angular momentum dissipation takes place in a hot corona that carries a small amount of the accreting mass. Here I discuss the formation of…
In the innermost regions of Active Galactic Nuclei (AGN), matter is understood to be flowing onto the Supermassive black hole (SMBH), which forms an accretion disk. This disk is responsible for the optical/UV continuum emission observed in…
We have calculated the relativistic reflection component of the X-ray spectra of accretion disks in active galactic nuclei (AGN). Our calculations have shown that the spectra can be significantly modified by the motion of the accretion flow…
X-ray reflection generates much of the spectral complexity in the X-ray spectra of AGN. It is argued that strong relativistic blurring of the reflection spectrum should commonly be expected from objects accreting at a high Eddington rate.…
Accretion states, which are universally observed in stellar-mass black holes in X-ray binaries, are also anticipated in active galactic nuclei (AGN). This is the case at low luminosities, when the jet-corona coupling dominates the energy…
An accretion flow onto a supermassive black hole is the primary process powering quasars. However, a geometry of this flow is not well constrained. Both global MHD simulations and observations suggest that there are several emission…
When Beppo-SAX measured the 0.1--12 keV spectrum of RE J1034+396, observations in the optical, UV and EUV were also taken within a few weeks. This multiwavelength spectrum placed very strong constraints on its unusually hot big blue bump…
We discuss the expected X-ray spectral and variability properties of black hole accretion discs at high luminosity, under the hypothesis that radiation pressure dominated discs are subject to violent clumping instabilities and, as a result,…
Active galactic nuclei (AGN) light curves observed with different wavebands show that the variability in longer wavelength bands lags the variability in shorter wavelength bands. Measuring these lags, or reverberation mapping, is used to…
The characteristic timescale ($\tau$) of continuum variability of the accretion disk in active galactic nuclei (AGNs) is known to be related to the thermal timescale, which is predicted to scale with AGN luminosity ($L$) and restframe…
Any cold, optically-thick matter in the vicinity of an accreting black hole, such as the accretion disk, can intercept and reprocess some fraction of the hard X-ray continuum emission, thereby imprinting atomic features into the observed…
Several active galactic nuclei show correlated variations in the ultraviolet/optical range, with time delays increasing at longer wavelengths. Thermal reprocessing of the X-rays illuminating the accretion disk has been proposed as a viable…
(abridged) The soft excess seen in the X-ray spectra of many high mass accretion rate AGN can be well modelled by reflection from a partially ionised accretion disc. However, the derived parameters are often extreme, both in terms of the…
Accretion disks in AGN should be subject to the same type of instability as in cataclysmic variables (CVs) or in low-mass X-ray binaries (LMXBs), which leads to dwarf nova and soft X-ray transient outbursts. It has been suggested that this…
Thermal reverberation in accretion discs of active galactic nuclei is thought to be the reason of the continuum UV/optical time lags seen in these sources. Recently, we studied thermal reverberation of a standard Novikov-Thorne accretion…
The non linear correlation between the UV and X-ray emission observed in Active Galactic Nuclei remains a puzzling question that challenged accretion models. While the UV emission originates from the cold disk, the X-ray emission is emitted…
We present an improved calculation of the vertical structure and ultraviolet spectrum of a dissipative accretion disk in an AGN. We calculate model spectra in which the viscous stress is proportional to the total pressure, the gas pressure…