Now You See It, Now You Don't: The Disappearing Central Engine of the
  Quasar J1011+5442
  We report the discovery of a new "changing-look" quasar, SDSS
J101152.98+544206.4, through repeat spectroscopy from the Time Domain
Spectroscopic Survey. This is an addition to a small but growing set of quasars
whose blue continua and broad optical emission lines have been observed to
decline by a large factor on a time scale of approximately a decade. The 5100
Angstrom monochromatic continuum luminosity of this quasar drops by a factor of
> 9.8 in a rest-frame time interval of < 9.7 years, while the broad H-alpha
luminosity drops by a factor of 55 in the same amount of time. The width of the
broad H-alpha line increases in the dim state such that the black hole mass
derived from the appropriate single-epoch scaling relation agrees between the
two epochs within a factor of 3. The fluxes of the narrow emission lines do not
appear to change between epochs. The light curve obtained by the Catalina Sky
Survey suggests that the transition occurs within a rest-frame time interval of
approximately 500 days. We examine three possible mechanisms for this
transition suggested in the recent literature. An abrupt change in the
reddening towards the central engine is disfavored by the substantial
difference between the timescale to obscure the central engine and the observed
timescale of the transition. A decaying tidal disruption flare is consistent
with the decay rate of the light curve but not with the prolonged bright state
preceding the decay, nor can this scenario provide the power required by the
luminosities of the emission lines. An abrupt drop in the accretion rate onto
the supermassive black hole appears to be the most plausible explanation for
the rapid dimming.
