Transient fading X-ray emission detected during the optical rise of a tidal disruption event

Journal Article · 02 April 2024 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/stae927 · OSTI ID:2352508

Malyali, A. ; Rau, A.; Bonnerot, C.; Goodwin, A. J.; Liu, Z.; Anderson, G. E. ; Brink, J.; Buckley, D. A. H. ; Merloni, A.; Miller-Jones, J. C. A. ; Grotova, I.; Kawka, A.

ABSTRACT We report on the SRG/eROSITA detection of ultra-soft ($$kT=47^{+5}_{-5}$$ eV) X-ray emission (LX =$$2.5^{+0.6}_{-0.5} \times 10^{43}$$ erg s−1) from the tidal disruption event (TDE) candidate AT 2022dsb ∼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 ∼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 Å emission complex with respect to the pre-outburst spectrum. Despite the early drop in the observed X-ray flux, the He ii 4686  Å complex is still detected for ∼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 α emission lines in a pre-peak optical spectrum, (ii) transient radio emission, and (iii) blueshifted Ly α absorption lines. The joint evolution of this early-time X-ray emission, the He ii 4686 Å 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.

• Sponsoring Organization: USDOE
• OSTI ID: 2352508
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 1 Vol. 531; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English