Galactic X-ray transients in the first eROSITA all sky survey

ABSTRACT Although a multitude of studies have focused on targeted observations of Galactic X-ray transients, blind surveys, and population studies have been limited. We have used the ROSAT, eROSITA, and Gaia source catalogues to find Galactic X-ray transients having time-scales $<$30 yr. We report the properties of 738 transients found in our search, majority of which are active stars or interacting binaries. We have also found $\sim$40 compact object systems among which are at least 8 newly identified white-dwarf systems, 3 known X-ray binaries, and 1 known pulsar. We use eROSITA (soft X-ray) spectra of the Galactic transients to show that two distinct types of flaring systems are prevalent: one having peak around 1 keV, well fit by thermal models, and another having peak below 0.2 keV and requiring a power-law component. Our study also reveals that single star or interacting binary systems (X-ray transients) involving giant stars exhibit significantly higher X-ray luminosities than systems involving only main-sequence stars or young stellar objects. Finally, we discuss the properties of the transients in the context of their putative emission mechanisms, the fraction of transients with respect to the total population, and the rates of Galactic transients expected in blind searches of the X-ray sky.