Speaker
Description
Recent years have seen broad observational support for the
circumnuclear gas around supermassive black holes to contain a clumpy
component. In the X-ray band, individual clouds can manifest
themselves when they transit the line of sight to the X-ray corona,
temporarily obscuring the X-ray continuum, and indicating the
characteristics and location of these clouds.
The eROSITA X-ray telescope aboard Spectrum X/Gamma is performing
multiple all-sky X-ray surveys, including monitoring a vast sample of
AGN and galaxies. Such monitoring can amplify rare cloud occultation
events, allowing us to accumulate observational constraints for
clumpy-torus models, including cloud distribution and composition
parameters.
Here, we discuss the first cloud occultation events detected in a
Seyfert 1 galaxy by eROSITA: in this Seyfert, the soft X-ray flux
dipped abruptly for $\sim$ 10-18 months during 2020-2021, recovered,
but then dropped a second time by Spring 2022. Our two-year
multi-wavelength follow-up campaign included X-ray/UV and ground-based
optical photometric and spectroscopic observations, and confirmed that
the soft X-ray flux dips were caused by partial-covering obscuration
by two separate, single compact clouds near the black hole.
The two transiting clouds are consistent with neutral or lowly-ionized
gas, residing at radial distances commensurate with the optical Broad
Line Region and the inner dusty torus, respectively.
