A Time-Tagged Database Of Every GALEX Photon Event ("gPhoton")

The Galaxy Evolution Explorer (GALEX) mission surveyed the sky in the ultraviolet for approximately ten years between April 2003 and June 2013. Its two microchannel plate (MCP) detectors recorded the position and time-of-arrival of incident photons ("photon events") with a time resolution of 5 thousandths of a second. Due to storage space and processing limitations, however, these data have previously been released and archived almost exclusively as integrated images (with visit- and coadd-level depths of minutes or more). The gPhoton database and associated software tools now give researchers the means to use photon-level GALEX data up through General Release (GR) 6/7.

The corpus of GR 6/7 photon data is composed of more than 79 billion FUV and over a trillion NUV photon events. On disk, the gPhoton database is approximately 130 TB. The gPhoton command line tools permit users to search for coverage within this database and create calibrated light curves, images, or movies (image cubes), with the flexibility to set time and spatial ranges or cuts across the entire mission. This enables studies of variability at timescales shorter than the GALEX visit files, customization or refinement of the calibration, and simplifies the fusion of data across mission phases, surveys and modes. When imported as Python modules, gPhoton permits even more detailed work with the data, including analysis at the level of individual photons.

星系演化探测器（Galaxy Evolution Explorer, GALEX）任务于2003年4月至2013年6月间开展了约十年的紫外波段巡天观测。其搭载的两台微通道板（microchannel plate, MCP）探测器以千分之五秒的时间分辨率，记录了入射光子的位置与到达时间，即“光子事件”。然而受限于存储空间与处理能力，此前该数据集几乎仅以积分图像的形式发布并归档，观测时段与叠加层级的积分时长可达数分钟甚至更久。如今gPhoton数据库及配套软件工具，为研究人员提供了调用通用发布版6/7（General Release 6/7, GR 6/7）级光子级GALEX数据的途径。

GR 6/7级光子数据集包含超过790亿个远紫外（FUV）光子事件与逾万亿个近紫外（NUV）光子事件。gPhoton数据库的磁盘占用约为130 TB。该工具的命令行版本支持用户在数据库中检索观测覆盖范围，并生成经过校准的光变曲线、图像或图像立方体（image cubes），可灵活设定时间与空间范围，或针对整个任务周期进行筛选。这一功能支持对短于GALEX观测时段的时间尺度上的天体光变开展研究，可自定义或优化校准流程，同时简化了不同任务阶段、巡天项目与观测模式间的数据融合工作。若将gPhoton作为Python模块（Python modules）导入，则可实现更精细化的数据处理，包括针对单个光子的分析。