Speaker
Description
The broad-band emission (optical/UV to X-ray) of luminous active galactic nuclei (AGNs) is believed to be powered by accretion onto central supermassive black holes, with the optical/UV emission generally explained as from the standard accretion disc, and the X-ray emission often explained as the inverse Compton scattering of the soft photons from the accretion disc in a hot corona above. This talk contains mainly two topics. Firstly, we performed a detailed study on the physical origin of the optical/UV-to-X-ray emission of luminous AGNs based on a sample composed of 23 type I Seyfert galaxies. Our work reveal that the optical/UV emission can be well fitted by a modified disc model with the radial temperature profile Teff(R) ∝ R^{-p} (with p~0.5-0.75, and a median of 0.63), deviating from the predication of the standard disk model of p=0.75 (2) the simultaneous optical/UV-to-X-ray emission can be well fitted by our refined disc-corona model with the corona heated by the magnetic reconnection. Secondly, we will present a recent study on a highly variable low-luminosity AGN NGC 7589, which showed a very strong X-ray variability with flux varied by a factor of over 100 within several months. Multi-epoch optical spectroscopic observations reveal no signs of Seyfert type change, however. The physical origin of the extreme variability remains mysterious and requires further, in-depth investigations.
