gPhoton: The GALEX Photon Data Archive

TL;DR

gPhoton is a comprehensive, Python-based database and software package that allows detailed analysis of GALEX ultraviolet photon data at high temporal resolution, enabling new time-domain astrophysics research.

Contribution

It introduces a new calibration pipeline, a large photon database, and analysis tools that improve access and analysis of GALEX UV data at the photon level, diverging from prior mission pipelines.

Findings

Database contains ~1.1 trillion photons with 5 ms resolution

Calibration pipeline reproduces original mission data reduction

Demonstrated new flare detection from M dwarf CR Draconis

Abstract

gPhoton is a new database product and software package that enables analysis of GALEX ultraviolet data at the photon level. The project's stand-alone, pure-Python calibration pipeline reproduces the functionality of the original mission pipeline to reduce raw spacecraft data to lists of time-tagged, sky-projected photons, which are then hosted in a publicly available database by the Mikulski Archive at Space Telescope (MAST). This database contains approximately 130 terabytes of data describing approximately 1.1 trillion sky-projected events with a timestamp resolution of five milliseconds. A handful of Python and command line modules serve as a front-end to interact with the database and to generate calibrated light curves and images from the photon-level data at user-defined temporal and spatial scales. The gPhoton software and source code are in active development and publicly available under a permissive license. We describe the motivation, design, and implementation of the calibration pipeline, database, and tools, with emphasis on divergence from prior work, as well as challenges created by the large data volume. We summarize the astrometric and photometric performance of gPhoton relative to the original mission pipeline. For a brief example of short time domain science capabilities enabled by gPhoton, we show new flares from the known M dwarf flare star CR Draconis. The gPhoton software has permanent object identifiers with the ASCL (ascl:1603.004) and DOI (doi:10.17909/T9CC7G). This paper describes the software as of version v1.27.2.