Speaker
Description
AGN are known to show flux variability over all observable timescales and across the entire electromagnetic spectrum. Over the past decade, a growing number of sources have been observed to show dramatic flux and spectral changes, both in the X-rays and in the optical/UV. Such events, commonly described as “changing-look AGN”, can be divided into two well-defined classes. Changing-obscuration objects show strong variability of the line-of-sight column density, mostly associated with clouds or outflows eclipsing the central engine of the AGN. Changing-state AGN are instead objects in which the optical/UV continuum emission and broad emission lines appear or disappear, and are typically triggered by strong changes in the accretion rate of the supermassive black hole. In addition to these, other rare classes of AGN transients have been discovered, including AGN flares potentially associated with extreme accretion events, or tidal disruption events occurring in active nuclei. The upcoming era of LSST is expected to significantly expand the discovery space for all these phenomena, thanks to its unparalleled cadence and depth. In my talk I will review our current understanding of Changing-state AGN, and then focus on future developments with LSST, particularly in combination with new-generation optical spectroscopic follow-up surveys (e.g. 4MOST).