SRG/erosita prospects for the detection of stellar tidal disruption flares

Abstract

We discuss the potential of the Extended ROentgen Survey with An Imaging Telescope Array (eROSITA) telescope on board the Spectrum-Roentgen-Gamma (SRG) observatory to detect stellar tidal disruption events (TDE) during its 4-year all-sky survey. These events are expected to reveal themselves as luminous flares of UV/soft X-ray emission associated with the centres of previously non-active galaxies and fading by a few orders of magnitude on time-scales of several months to years. Given that eROSITA will complete an all-sky survey every 6 months and a total of eight such scans will be performed over the course of the mission, we propose to distinguish TDEs from other X-ray transients using two criteria: (i) large (more than a factor of 10) X-ray variation between two subsequent 6-month scans and (ii) soft X-ray spectrum. The expected number of TDE candidates is ~103 per scan (with most of the events being new discoveries in a given scan), so that a total of several thousand TDE candidates could be found during the 4-year survey. The actual number may significantly differ from this estimate, since it is based on just a few TDEs observed so far. The eROSITA all-sky survey is expected to be nearly equally sensitive to TDEs occurring near supermassive black holes (SMBH) of mass between ~106 and ~107M⊙ and will thus provide a unique census of quiescent SMBHs and associated nuclear stellar cusps in the local Universe (z ≲ 0.15). Information on TDE candidates will be available within a day after their detection and localization by eROSITA, making possible follow-up observations that may reveal peculiar types of TDEs. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.