We describe the calibration status and data products pertaining to the GR2
and GR3 data releases of the Galaxy Evolution Explorer (GALEX). These releases
have identical pipeline calibrations that are significantly improved over the
GR1 data release. GALEX continues to survey the sky in the Far Ultraviolet
(FUV, ~154 nm) and Near Ultraviolet (NUV, ~232 nm) bands, providing
simultaneous imaging with a pair of photon counting, microchannel plate, delay
line readout detectors. These 1.25 degree field-of-view detectors are
well-suited to ultraviolet observations because of their excellent red
rejection and negligible background. A dithered mode of observing and photon
list output pose complex requirements on the data processing pipeline,
entangling detector calibrations and aspect reconstruction algorithms. Recent
improvements have achieved photometric repeatability of 0.05 and 0.03 mAB in
the FUV and NUV, respectively. We have detected a long term drift of order 1%
FUV and 6% NUV over the mission. Astrometric precision is of order 0.5" RMS in
both bands. In this paper we provide the GALEX user with a broad overview of
the calibration issues likely to be confronted in the current release.
Improvements are likely as the GALEX mission continues into an extended phase
with a healthy instrument, no consumables, and increased opportunities for
guest investigations.Comment: Accepted to the ApJS (a special GALEX issue