eRO-ExTra catalog

When possible, transients are associated with optical LS10 counterparts. The properties of these counterparts are used to exclude stars and known active galaxies. The sample is additionally cleaned from known AGN using pre-eROSITA SIMBAD and the Million Quasars Catalog (Milliquas) classifications, archival optical spectra, and archival X-ray data.

We explore archival X-ray variability, long-term (2-2.5 years) eROSITA light curves, and peak X-ray spectra to characterize the X-ray properties of the sample. Sources with radio counterparts are identified using the Rapid ASKAP Continuum Survey (RACS) and Karl G. Jansky Very Large Array Sky Survey (VLASS). We present a catalog of 304 extragalactic eROSITA transients and variables not associated with known AGN, called eRO-ExTra.

More than 90% of sources are associated with reliable LS10 optical counterparts. For each source, we provide archival X-ray data from Swift, ROSAT, and XMM-Newton, the eROSITA long-term light curve with light curve classification, as well as the best power law fit spectral results at the peak eROSITA epoch. Reliable spectroscopic and photometric redshifts, both archival and from follow-up data, are provided for more than 80% of the sample.

Several sources in the catalog are eROSITA discovered known TDE candidates. In addition, 31 sources are radio detected. The origin of radio emission needs to be further identified.

The eRO-ExTra transients constitute a relatively clean parent sample of non-AGN variability phenomena associated with massive black holes. The eRO-ExTra catalog includes more than 95% of sources discovered in X-rays with eROSITA for the first time, making it a valuable resource for studying unique nuclear transients.