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Free keywords:
BLACK-HOLES; RADIO OBSERVATIONS; LIGHT CURVES; FOLLOW-UP; E PLUS;
STELLAR; ABSORPTION; OUTFLOW; MODEL; DISCOVERYAstronomy & Astrophysics; accretion, accretion discs; black hole physics; galaxies: nuclei;
transients: tidal disruption events;
Abstract:
We report on the SRG/eROSITA detection of ultra-soft kT=47(-5)(+5)eVX-ray emission (LX=2.5(-0.5)(+0.6)x10(43)ergs(-1)) from the tidal disruption event (TDE) candidate AT 2022dsb similar to 14 d before peak optical brightness. As the optical luminosity increases after the eROSITA detection, then the 0.2-2 keV observed flux decays, decreasing by a factor of similar to 39 over the 19 d after the initial X-ray detection. Multi-epoch optical spectroscopic follow-up observations reveal transient broad Balmer emission lines and a broad He ii 4686 & Aring; emission complex with respect to the pre-outburst spectrum. Despite the early drop in the observed X-ray flux, the He ii 4686 & Aring; complex is still detected for similar to 40 d after the optical peak, suggesting the persistence of an obscured hard ionizing source in the system. Three outflow signatures are also detected at early times: (i) blueshifted H alpha emission lines in a pre-peak optical spectrum, (ii) transient radio emission, and (iii) blueshifted Ly alpha absorption lines. The joint evolution of this early-time X-ray emission, the He ii 4686 & Aring; complex, and these outflow signatures suggests that the X-ray emitting disc (formed promptly in this TDE) is still present after optical peak, but may have been enshrouded by optically thick debris, leading to the X-ray faintness in the months after the disruption. If the observed early-time properties in this TDE are not unique to this system, then other TDEs may also be X-ray bright at early times and become X-ray faint upon being veiled by debris launched shortly after the onset of circularization.
