The Sloan Digital Sky Survey Reverberation Mapping Project: Systematic
  Investigations of Short-Timescale CIV Broad Absorption Line Variability
  We systematically investigate short-timescale ($<$10-day rest-frame) CIV
broad absorption-line (BAL) variability to constrain quasar-wind properties and
provide insights into BAL-variability mechanisms in quasars. We employ data
taken by the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project,
as the rapid cadence of these observations provides a novel opportunity to
probe BAL variability on shorter rest-frame timescales than have previously
been explored. In a sample of 27 quasars with a median of 58 spectral epochs
per quasar, we have identified 15 quasars ($55^{+18}_{-14}$%), 19 of 37 CIV BAL
troughs ($51^{+15}_{-12}$%), and 54 of 1460 epoch pairs ($3.7 \pm 0.5$%) that
exhibit significant CIV BAL equivalent-width variability on timescales of less
than 10 days in the quasar rest frame. These frequencies indicate that such
variability is common among quasars and BALs, though somewhat rare among epoch
pairs. Thus, models describing BALs and their behavior must account for
variability on timescales down to less than a day in the quasar rest frame. We
also examine a variety of spectral characteristics and find that in some cases,
BAL variability is best described by ionization-state changes, while other
cases are more consistent with changes in covering fraction or column density.
We adopt a simple model to constrain the density and radial distance of two
outflows appearing to vary by ionization-state changes, yielding outflow
density lower limits consistent with previous work.
