The time-variable ultraviolet sky: Active Galactic Nuclei, Stars and White Dwarfs

TL;DR

This paper introduces the 1UVA catalog of 4202 time-variable UV sources from 10 years of GALEX data, highlighting the discovery of UV variability in White Dwarfs and the development of a new analysis pipeline, VASCA.

Contribution

The paper presents a novel analysis pipeline, VASCA, and the first comprehensive catalog of time-variable UV sources, including the detection of variability in White Dwarfs.

Findings

4202 UV variable sources detected.

UV variability observed in four White Dwarfs.

One White Dwarf shows unexpected flux variability.

Abstract

Here, we present the 1UVA catalog of time variable ultraviolet (UV) sources. We describe a new analysis pipeline, the VAriable Source Clustering Analysis (VASCA). We apply the pipeline to 10 years of data from the GALaxy Evolution eXplorer (GALEX) satellite. We analyse a sky area of 302 deg$^2$ , resulting in the detection of 4202 time-variable UV sources. We cross correlate these sources with multi-frequency data from the Gaia satellite and the SIMBAD database, finding an association for 3655 sources. The source sample is dominated by Active Galactic Nuclei ($\approx$73 %) and stars ($\approx$24 %). We look at UV and multi-frequency properties of these sources, focusing on the stellar population. We find UV variability for four White Dwarfs. One of them, WD J004917.14-252556.81, has recently been found to be the most massive pulsating White Dwarf. Its Spectral Energy Distribution shows no sign of a stellar companion. The observed flux variability is unexpected and difficult to explain.