The Calibration and Data Products of Galex

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 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 FUVand NUV, respectively. We have detected a long-term drift of order 1% FUVand 6% NUVover the mission. Astrometric precision is of order 0.500 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. Subject headingg s: space vehicles — surveys — telescopes — ultraviolet: general Online material: color figures