Astrophys. J., 909, 102-102 (2021/March-2)
A luminous X-ray transient in SDSS J143359.16+400636.0 a likely tidal disruption event.
BRIGHTMAN M., WARD C., STERN D., MOOLEY K., DE K., GEZARI S., VAN VELZEN S., ANDREONI I., GRAHAM M., MASCI F.J., RIDDLE R. and ZOLKOWER J.
Abstract (from CDS):
We present the discovery of a luminous X-ray transient, serendipitously detected by Swift's X-ray Telescope on 2020 February 5, located in the nucleus of the galaxy SDSS J143359.16+400636.0 at z = 0.099 (luminosity distance DL = 456 Mpc). The transient was observed to reach a peak luminosity of ∼1044 erg s–1 in the 0.3-10 keV X-ray band, which was ∼20 times more than the peak optical/UV luminosity. Optical, UV, and X-ray light curves from the Zwicky Transient Facility and Swift show a decline in flux from the source consistent with t–5/3, and observations with NuSTAR and Chandra show a soft X-ray spectrum with photon index Γ = 2.9 ± 0.1. The X-ray/UV properties are inconsistent with well-known active galactic nucleus properties and have more in common with known X-ray tidal disruption events (TDEs), leading us to conclude that it was likely a TDE. The broadband spectral energy distribution can be described well by a disk blackbody model with an inner disk temperature of 7.3–0.8+0.3×105 K, with a large fraction (>40%) of the disk emission upscattered into the X-ray band. An optical spectrum taken with Keck/LRIS after the X-ray detection reveals LINER line ratios in the host galaxy, suggesting low-level accretion onto the supermassive black hole prior to the event, but no broad lines or other indications of a TDE were seen. The stellar velocity dispersion implies that the mass of the supermassive black hole powering the event is log(MBH/M☉) = 7.41 ± 0.41, and we estimate that at peak the Eddington fraction of this event was ∼50%. This likely TDE was not identified by wide-field optical surveys or optical spectroscopy, indicating that more events like this would be missed without wide-field UV or X-ray surveys.
© 2021. The American Astronomical Society. All rights reserved.
Tidal disruption - X-ray transient sources - Transient sources - X-ray sources - Supermassive black holes
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