The eROSITA Final Equatorial-Depth Survey (eFEDS): The variability catalogue and multi-epoch comparison

TL;DR

This paper presents a comprehensive analysis of X-ray variability in the eFEDS survey, identifying significantly variable sources and characterizing their properties across multiple epochs and energy bands.

Contribution

It introduces a detailed variability catalog for eFEDS sources, applying multiple statistical methods and providing multi-epoch comparison data for the first time.

Findings

65 sources significantly variable in soft band

Only one source varies significantly in hard band

Detection of extreme stellar flare events and variable AGN

Abstract

The 140 square degree Final Equatorial-Depth Survey (eFEDS) field, observed with the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) aboard the Spectrum-Roentgen-Gamma (SRG) mission, provides a first look at the variable eROSITA sky. We analyze the intrinsic X-ray variability of the eFEDS sources, provide X-ray light curves and tables with variability test results in the 0.2-2.3 keV (soft) and 2.3-5.0 keV (hard) bands. respectively. We perform variability tests using the normalized excess variance and maximum amplitude variability methods as performed for the 2RXS catalogue and add results from the Bayesian excess variance and the Bayesian block methods. In total 65 sources have been identified as being significantly variable in the soft band. In the hard band only one source is found to vary significantly. For the most variable sources fits to stellar flare events reveal extreme flare properties. A few highly variable AGN have also been detected. About half of the variable eFEDS sources have been detected at X-rays with eROSITA for the first time. Comparison with 2RXS and XMM observations provide variability information on timescales of years to decades.