| Name: | Tathagata Saha |
| Affiliation: | Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences |
| Conference ID : | ASI2023_188 |
| Title : | Multiwavelength follow-up studies of eROSITA detected AGN transients |
| Authors : | Tathagata Saha , Alex G. Markowitz, David Homan, Mirko Krumpe, Matthew Graham , Steven Hammerich, Sara Frederick, Mariuz Gromadzki, Joern Wilms, Hartmut Winkler, Suvi Gezari, Arne Rau, Adam Malyali, Zhu Liu, Iullia Grotova |
| Mode of Presentation: | Oral |
| Abstract Category : | Extragalactic Astronomy |
| Abstract : | Active galactic nuclei (AGNs) accrete persistently over a long timescale (105-106 years). During its lifetime, an AGN exhibits stochastic variability up to a few percent. However, there are sources where variability of orders of magnitude (>~10) accompanied by a Seyfert type change has been observed. Extreme variability is often associated with either a change in accretion structure (a changing state event) or due to occultation by a cloud from the torus or the BLR (a changing obscuration event). In most cases, detection of such extremely variable AGN transients have been serendipitous. But with the advent of eROSITA the search for extreme transients has become more systematic. The eROSITA X-ray telescope aboard Spectrum X/Gamma is conducting all-sky scans every six months. Using these scans, we detect extreme extragalactic AGN transients as they are happening. Subsequently, we trigger multiple follow-up X-ray observations using XMM-Newton, Swift, NICER, SALT and optical spectroscopic and photometric follow-up observations, to carry out extensive long term monitoring. Here, we present a few candidate ignition and shutdown events detected with eROSITA and followed up by our multiwavelength observation campaigns. In these sources, we track the changes in emission from various AGN substructures like the accretion disk, corona, broad line region and the torus in real time as they respond to significant changes in the accretion flow or torus eclipse events. Our research thus helps discern the various modes of accretion onto supermassive black holes, the properties of the broad line emitter and in general, the morphology of the circumnuclear gas. |
