SHAO Astrophysics Colloquium

Title: Self-consistent calculations of Comptonised spectra of extended AGN coronae in Kerr spacetime

Speaker: Dr. Wenda Zhang (Astronomical Institute, Czech Academy of Sciences)

Time: 3 pm, March 7 (Thursday)

Location: Lecture Hall, 3rd floor

Abstract: The X-ray radiation of the AGNs and black hole X-ray binaries is originating from the innermost region of the accretion flow in the vicinity of the black hole, where the strong gravitational field plays an important role. Therefore, the X-ray emission contains information of the strong gravitational field as well as the accretion flow, and by analyzing the X-ray emission we can potentially put constraints on the properties of the black holes. One of the best examples is measuring the black hole spin by fitting the broad iron K fluorescent line profile. In some AGNs, especially narrow-line Seyfert 1 galaxies, to fit the broad iron line profile steep radial emissivity is required. Therefore in many studies, people make the simplification that the corona, which is generally believed to be responsible for the hard X-ray emission in AGNs by Comptonising the soft seed photons, is an isotropic, point-like source on the black hole rotation axis; this is known as the lamp-post scenario. In this scenario, the general relativistic calculations are greatly simplified. The energy spectrum of the corona is usually modeled by a powerlaw with low- and high-energy cutoffs. To perform more self-consistent and realistic calculations of Comptonised spectra of extended coronae, we develop a Monte Carlo radiative transfer code, MONK. We assume the Klein-Nishina cross section and include all general relativistic effects. In this talk, I will show that according to our calculations, the angular distribution and energy spectra may be distinct with an isotropic source with simple powerlaw spectrum, which will affect the size estimation of the corona as well as modeling of the reflection spectrum.