Abstract for Proposal 090251

Extreme AGN Fading from eROSITA

Spectrum-Roentgen Gamma (SRG) is, for the next two years, providing the unique ability to identify highly variable X-ray sources across the full sky at depths significantly fainter than Swift/BAT or MAXI. We propose here for six XMM-Newton + NuSTAR coordinated target-of opportunity (ToO) observations of AGN that have shown significant (>10x) fading between eROSITA passes. Broad-band data from XMM-Newton + NuSTAR will robustly determine whether the fading is due to variable extinction, which provides a probe of the clumpy torus structure, or a true decrease in the intrinsic X-ray emission due to fading or collapse of the central engine.

Details on Observing Strategy and Trigger Criteria
Our trigger criteria are: (1) an initial eROSITA soft X-ray flux of f(0.3-2.2 kev) > 1e-12 erg/cm2/s, and (2) a drop in this flux by a factor of >10× between eROSITA sky passes (i.e., 6 months). We request a reaction time within 14 days. The joint NuSTAR observations do not need to be strictly simultaneous.