An Active Galactic Nucleus Caught in the Act of Turning Off and On
  We present the discovery of an active galactic nucleus (AGN) that is turning
off and then on again in the z=0.06 galaxy SDSS J1354+1327. This episodic
nuclear activity is the result of discrete accretion events, which could have
been triggered by a past interaction with the companion galaxy that is
currently located 12.5 kpc away. We originally targeted SDSS J1354+1327 because
its Sloan Digital Sky Survey spectrum has narrow AGN emission lines that
exhibit a velocity offset of 69 km s$^{-1}$ relative to systemic. To determine
the nature of the galaxy and its velocity-offset emission lines, we observed
SDSS J1354+1327 with Chandra/ACIS, Hubble Space Telescope/Wide Field Camera 3,
Apache Point Observatory optical longslit spectroscopy, and Keck/OSIRIS
integral-field spectroscopy. We find a ~10 kpc cone of photoionized gas south
of the galaxy center and a ~1 kpc semi-spherical front of shocked gas, which is
responsible for the velocity offset in the emission lines, north of the galaxy
center. We interpret these two outflows as the result of two separate AGN
accretion events; the first AGN outburst created the southern outflow, and then
$<10^5$ yrs later the second AGN outburst launched the northern shock front.
SDSS J1354+1327 is the galaxy with the strongest evidence for an AGN that has
turned off and then on again, and it fits into the broader context of AGN
flickering that includes observations of AGN light echoes.
