PS1-13cbe: The Rapid "Turn on" of a Seyfert 1
  We present a nuclear transient event, PS1-13cbe, that was first discovered in
the Pan-STARRS1 survey in 2013. The outburst occurred in the nucleus of the
galaxy SDSS J222153.87+003054.2 at $z = 0.12355$, which was classified as a
Seyfert 2 in a pre-outburst archival Sloan Digital Sky Survey (SDSS) spectrum.
PS1-13cbe showed the appearance of strong broad H$\alpha$ and H$\beta$ emission
lines and a non-stellar continuum in a Magellan spectrum taken 57 days after
the peak of the outburst that resembled the characteristics of a Seyfert 1.
These broad lines were not present in the SDSS spectrum taken a decade earlier
and faded away within two years, as observed in several late-time MDM spectra.
We argue that the dramatic appearance and disappearance of the broad lines and
factor of $\sim 8$ increase in the optical continuum is most likely caused by
variability in the pre-existing accretion disk than a tidal disruption event,
supernova, or variable obscuration. The timescale for the turn-on of the
optical emission of $\sim 70$ days observed in this transient is among the
shortest observed in a "changing look" active galactic nucleus.
