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February 8, 2019 | 3:30 p.m. - 4:30 p.m.
Category: Seminar
Location: Physics & Astronomy Department - Liberal Arts and Sciences #312 | Map
666 W. Hancock
Detroit, MI 48201
Cost: Free
Audience: Academic Staff, Current Graduate Students, Current Undergraduate Students, Faculty

Title: X-Ray Obscuration in Active Galactic Nuclei

Speaker: Dr. Elias Kammoun (University of Michigan)

Abstract: It is commonly thought that “type 2” active galactic nuclei (AGN) are usually obscured in X-rays by material with high column densities (NH), whose exact location and distribution remain an open question. The obscuring material is generally identified with dusty molecular “torus” at the parsec scale, within the “Unification Scenarios” of AGN. However, several pieces of evidence challenge this interpretation. In particular, a handful of AGN have shown rapid changes in column density that are in favor of a clumpy distribution of optically-thick clouds rather than a homogeneous structure. The NH-variability timescale suggests that the material is located closer distances to the supermassive black hole (SMBH) which are consistent with the broad line region (BLR). In this context, the passage of a BLR-gas cloud in our line of sight, that is orbiting the SMBH, will not affect only the AGN’s light curve but it shows also a strong impact on its spectroscopic and polarimetric properties. In fact, as the cloud moves in our line of sight it will shade different regions of the accretion disc, which will allow us to probe the innermost regions close to the SMBH. In my talk, I will present the X-ray spectral and polarimetric effects of such eclipsing events. Then, I will present the first results from a survey carried with the Nuclear Spectroscopic Telescope Array (NuSTAR) that aims to characterize the hard X-ray properties of obscured AGN in the local Universe. I will also discuss the role that future high-resolution X-ray observatories such as Athena and XARM will play in identifying and studying obscured AGN.

For more information about this event, please contact James Osborne at (313) 577-1409 or