PROFESSOR GULAB CHAND DEWANGAN

Active galactic nuclei (AGN) are the most powerful, continuously emitting objects in the Universe. They are powered by accretion onto super-massive black holes (SMBH) at the centres of active galaxies. The key ingredients of the AGN central engines - the accretion disk and the hot corona, emit in the UV to X-ray bands. The broadband UV/X-ray emission thus provides an opportunity to study complex processes occurring near the SMBH. X-rays arising from the compact, hot corona get reprocessed in the regions ranging from the vicinity of SMBH within a few Schwarzschild radii to outer accretion disks and the broad/narrow line regions. X-ray reflection from the innermost regions provides the direct probe of the strong gravity near the SMBH. The UV continuum emission either intrinsic or reprocessed and its connection with the X-ray emission can probe the nature of AGN disks, which have been assumed to be the standard Shakura-Sunyaev disks for the last 40 years. The speaker will discuss the X-ray/UV spectral and variability signatures that are used to unravel the AGN central engines, and the progress made based on recent X-ray/UV observations with XMM-Newton, Swift, NuStar, etc. He will also discuss the role of AstroSat X-ray/UV observations in understanding the AGN central engines.