The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Disk-Corona System

Yao Y, Lu W, Guolo M, Pasham DR, Gezari S, Gilfanov M, Gendreau KC, Harrison F, Cenko SB, Kulkarni SR, Miller JM, Walton DJ, Garcia J, Van Velzen S, Alexander KD, Miller-Jones JCA, Nicholl M, Hammerstein E, Medvedev P, Stern D, Ravi V, Sunyaev R, Bloom JS, Graham MJ, Kool EC, Mahabal AA, Masci FJ, Purdum J, Rusholme B, Sharma Y, Smith R, Sollerman J (2022)

Publication Type: Journal article

Publication year: 2022

Journal

Book Volume: 937

Journal Issue: 1

DOI: 10.3847/1538-4357/ac898a

Abstract

We present X-ray, UV, optical, and radio observations of the nearby (approximate to 78 Mpc) tidal disruption event AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy hosting a approximate to 10(7) M-circle dot black hole (M-BH 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 -> hard transition and then suddenly turns soft again within 3 days at delta t approximate to 272 days during which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (delta 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(-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 -> 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 (similar to a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger column density-the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the thermal-viscous instability in the inner accretion flow, leading to a much thinner disk.

Authors with CRIS profile

Involved external institutions

Princeton University United States (USA) (US) Russian Academy of Sciences / Росси́йская акаде́мия нау́к (RAS) Russian Federation (RU) Johns Hopkins University (JHU) United States (USA) (US) California Institute of Technology (Caltech) United States (USA) (US) Stockholm University / Stockholms universitet Sweden (SE) University of California, Berkeley United States (USA) (US) University of Birmingham United Kingdom (GB) Leiden University Netherlands (NL) Curtin University Australia (AU) University of Maryland United States (USA) (US) University of Hertfordshire United Kingdom (GB) National Aeronautics and Space Administration (NASA) United States (USA) (US) University of Michigan United States (USA) (US) Northwestern University United States (USA) (US) Massachusetts Institute of Technology (MIT) United States (USA) (US) Space Telescope Science Institute (STScI) United States (USA) (US)

How to cite

APA:

Yao, Y., Lu, W., Guolo, M., Pasham, D.R., Gezari, S., Gilfanov, M.,... Sollerman, J. (2022). The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Disk-Corona System. Astrophysical Journal, 937(1). https://dx.doi.org/10.3847/1538-4357/ac898a

MLA:

Yao, Yuhan, et al. "The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflection, and Rapid Evolution of the Disk-Corona System." Astrophysical Journal 937.1 (2022).

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