Seminars take place in the lecture room of the Spořilov building (see contacts) unless noted otherwise.

Scheduled seminars

Joint Journal Club


Location: Zoom

From the X-rays to the optical/UV: clues about the nature of the central source in AGN.

Iossif Papadakis

Active Galactic Nuclei are powered by accretion of matter to the supermassive black holes that reside at their center. The optical/UV "Big Blue Bump" component in their spectra is commonly interpreted as optically thick thermal radiation which arises in the region of steeply falling potential region near the black hole, and strongly supports the "accretion-powered" model. AGN are also strong X-ray emitters, but standard accretion disc models cannot account for them. The X-ray source must be powered by the mass accretion to the black hole, but we still do not know how or where the X-ray source is located. Monitoring X-ray/UV/optical observations the last few decades (as well as by the study of the reflection signatures in the X-ray spectra) have provided important clues regarding the disc/X-ray source geometry in AGN. I will discuss recent results from intense X-ray/UV/optical monitoring campaigns of bright AGN the last few years, and I will argue that proper treatment of the X-ray illumination of a "standard" accretion disc can explain them (contrary to what was believed in the past). I will also address the implication of X-ray illuminated disc models to the results from other challenging observations (like the "disc-size" problem implied by microlensing observations of lensed quasars etc).

Location: Zoom

If you would like to give a seminar, please contact Georgios Loukes-Gerakopoulos or Vladimír Karas.