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The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Diskâ€"Corona System.
- Source :
- Astrophysical Journal; 9/20/2022, Vol. 937 Issue 1, p1-25, 25p
- Publication Year :
- 2022
-
Abstract
- We present X-ray, UV, optical, and radio observations of the nearby (â‰78 Mpc) tidal disruption event AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy hosting aâ‰10<superscript>7</superscript> M <subscript>⊙</subscript> black hole (M <subscript>BH</subscript> inferred from host galaxy scaling relations). High-cadence Swift and Neutron Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first undergoes a gradual soft â†' hard transition and then suddenly turns soft again within 3 days at δ t â‰272 days during which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δ t = 264 days, harder state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of 6.0 â' 3.8 + 10.4 % L Edd when the X-ray spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical luminosity stays relatively constant, and the optical spectra are featureless. We propose the following interpretations: (i) the soft â†' hard transition may be caused by the gradual formation of a magnetically dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical depth (âĽa few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger column densityâ€"the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the thermalâ€"viscous instability in the inner accretion flow, leading to a much thinner disk. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 0004637X
- Volume :
- 937
- Issue :
- 1
- Database :
- Complementary Index
- Journal :
- Astrophysical Journal
- Publication Type :
- Academic Journal
- Accession number :
- 159137634
- Full Text :
- https://doi.org/10.3847/1538-4357/ac898a