| Abstract : | The spectral and temporal properties of X-ray/ultraviolet (UV)/optical emission from active galactic nuclei (AGNs) are key to understanding the nature of inflow toward their central super-massive black hole (SMBH). While the optical-UV emission is from the accretion disk the X-rays are presumably through inverse-Compton scattering of disk photons by a compact energetic particle distribution, termed "corona", located near the disk. AstroSat, India's first multi-wavelength space telescope, has been observing several AGNs simultaneously at X-ray and UV wave bands. Similar observations at different wave bands have been carried out by other observing facilities in the past. In order to interpret the spectral and temporal data accumulated by those observations, we present a theoretical model of the AGN accretion disk-corona system, in which fluctuations propagate down the accretion disk towards the central SMBH, resulting in the intrinsic variability of the disk emission. In addition, part of the coronal X-rays heats the disk and gives rise to additional optical-UV emission, in a process termed "reprocessing". The amount of reprocessed emission depends on the geometry of the disk-corona system. We compare the emission spectrum and variability simulated in our model to the observed data in order to put meaningful and stringent constraints on the structure and emission mechanisms of the accretion disk-corona system in Seyfert galaxies. |
