The Optical Variability of SDSS Quasars from Multi-epoch Spectroscopy.
  III. A Sudden UV Cutoff in Quasar SDSS J2317+0005
  We have collected near-infrared to X-ray data of 20 multi-epoch heavily
reddened SDSS quasars to investigate the physical mechanism of reddening. Of
these, J2317+0005 is found to be a UV cutoff quasar. Its continuum, which
usually appears normal, decreases by a factor 3.5 at 3000{\AA}, compared to its
more typical bright state during an interval of 23 days. During this sudden
continuum cut-off, the broad emission line fluxes do not change, perhaps due to
the large size of the Broad Line Region (BLR), r > 23 / (1+z) days. The UV
continuum may have suffered a dramatic drop out. However, there are some
difficulties with this explanation. Another possibility is that the intrinsic
continuum did not change, but was temporarily blocked out, at least towards our
line of sight. As indicated by X-ray observations, the continuum rapidly
recovers after 42 days. A comparison of the bright state and dim states would
imply an eclipse by a dusty cloud with a reddening curve having a remarkably
sharp rise shortward of 3500{\AA}. Under the assumption of being eclipsed by a
Keplerian dusty cloud, we characterized the cloud size with our observations,
however, which is a little smaller than the 3000\AA\ continuum-emitting size
inferred from accretion disk models. Therefore, we speculate this is due to a
rapid outflow or inflow with a dusty cloud passing through our line-of-sight to
the center.
