2015ApJ...803L..28G

We report on the Swift discovery of a second high-amplitude (factor 100) outburst of the Seyfert 1.9 galaxy IC 3599, and discuss implications for outburst scenarios. Swift detected this active galactic nucleus (AGN) again in 2010 February in X-rays at a level of (1.50±0.11)x 10³⁶ W (0.2-2.0 keV), which is nearly as luminous as the first outburst detected with ROSAT in 1990. Optical data from the Catalina sky survey show that the optical emission was already bright 2 yr before the Swift X-ray high state. Our new Swift observations performed between 2013 and 2015 show that IC 3599 is currently in a very low X-ray flux state once again. This repeat optical and X-ray outburst, and its long optical duration, suggest that IC 3599 is likely not a tidal disruption event. Instead, we explore variants of AGN-related variability. The data are consistent with accretion disk instability around a black hole of mass on the order of 10⁶-10⁷ M_☉; a value estimated using several different methods.