Speaker
Description
eROSITA has so far completed four all-sky X-ray surveys, detecting around one million AGN in each survey. We conduct a large-scale and systematic search among all individual surveys, to identify the most extreme X-ray variability events in extra-galactic objects. Among those are significant ignition and shut-down events associated with large changes in accretion rate or line-of-sight absorption. The most significant events are followed-up in a multi-wavelength campaign, which includes optical photometry & spectroscopy and observations in UV, and X-rays.
In this talk, I will cover the results of our search covering the first four eROSITA all-sky surveys. I will introduce our sample of extremely variable sources by detailing our selection methods. In total our sample consists of ~2,000 vetted sources, of which approximately 10% have additional multi-wavelength follow-up data. I will provide an overview of some of the most interesting sources detected (extreme ignition and shutdown events in AGN), which are currently published in several papers. I will also discuss our results in the context of the link between extreme X-ray and optical variability, specifically 'changing-look' behaviour in AGN, and the time-scales involved in large-scale accretion changes around SMBHs. Finally, I will introduce the first statistical study of the largest X-ray selected changing-look AGN sample to date. From this sample conclusions can be drawn on the occurrence rate of changing-look events, as well as their preferred AGN parameter space.
