The Calibration and Data Products of the Galaxy Evolution Explorer

TL;DR

This paper details the calibration processes, data products, and performance metrics of the GALEX ultraviolet space telescope, highlighting improvements over previous data releases and discussing ongoing calibration challenges.

Contribution

It provides a comprehensive overview of GALEX's calibration status, data products, and performance metrics, including recent improvements and future prospects.

Findings

Photometric repeatability of 0.05 and 0.03 mAB in FUV and NUV

Detected long-term drift of 1% in FUV and 6% in NUV

Astrometric precision of 0.5 arcseconds RMS

Abstract

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.