GALEX observations of quasar variability in the ultraviolet
  Using archival observations recorded over a 5+ year timeframe with the NASA
Galaxy Evolution Explorer (GALEX) satellite, we present a study of the
ultraviolet (UV) variability of 4360 quasars of redshifts up to z=2.5 that have
optical counterparts in the Sloan Digital Sky Survey DR5 spectroscopic catalog.
The observed changes in both the far UV (FUV: 1350-1785A) and near UV (NUV:
1770-2830A) AB magnitudes as a function of time may help differentiate between
models of the emission mechanisms thought to operate in these active galaxies.
A list of NUV and FUV variable quasars was derived from the UV light-curves of
sources with 5 or more observational visits by GALEX that spanned a time-frame
greater than 3 months. By measuring the error in the derived mean UV magnitude
from the series of GALEX observations for each source, quasars whose UV
variability was greater than the 3-sigma variance from the mean observed value
were deemed to be (intrinsically) UV variable. This conservative selection
criterion (which was applied to both FUV and NUV observations) resulted in
identifying 550 NUV and 371 FUV quasars as being statistically significant UV
variable objects.
