Wind-Driven Extreme X-ray Variability Events in Weak-Line Quasars

This is a recording of a talk titled "Wind-Driven Extreme X-ray Variability Events in Weak-Line Quasars" prepared for the "Black Hole Accretion Disk Winds" conference (2021 September; talk presented virtually owing to COVID-19). The speaker is Prof. W.N. Brandt from the Department of Astronomy & Astrophysics at the Pennsylvania State University. The talk has been prepared in collaboration Bin Luo (Nanjing University) and Qingling Ni (Penn State), who have made fundamental contributions to the work described. We also acknowledge our other helpful collaborators on this work, as listed in the talk itself.
Here is the relevant abstract: Investigations of the extraordinary properties of weak-line quasars (WLQs) have led us to put forward a model where a thick inner accretion disk, associated with a high Eddington ratio, is responsible for both their weak lines and varied X-ray properties. Such high-Eddington-ratio accretion is predicted to launch fast, wide-angle, disk winds, and WLQs show clear signatures of such winds; e.g., dramatic C IV emission-line shifts of thousands of km/s. I will describe how we have recently discovered extreme X-ray variability behavior from a few luminous WLQs (with billion solar-mass black holes) involving variations between X-ray weak and X-ray normal states with little accompanying optical/UV continuum or emission-line variability. This variability can be best understood via absorption by a rotating, azimuthally asymmetric disk wind observed near its launching radius. In one case, we have found large-amplitude variability within just two rest-frame days, requiring wind transverse motion at a significant fraction of the speed of light. WLQs seem to preferentially show extreme wind-driven variability events relative to matched typical radio-quiet quasars, and I will describe how ongoing multi-year Chandra monitoring is now exploring this behavior systematically.

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So incredibly glad to see you active and making content. That lecture on Active Galactic Nuclei is the best resource I have ever found on the topic. This work is appreciated.