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Abstract We present a systematic analysis of the X-ray emission of a sample of 17 optically selected, X-ray-detected tidal disruption events (TDEs) discovered between 2014 and 2021. The X-ray light curves show a diverse range of temporal behaviors, with most sources not following the expected power-law decline. The X-ray spectra are mostly extremely soft and consistent with thermal emission from the innermost region of an accretion disk, which cools as the accretion rate decreases. Three sources show formation of a hard X-ray corona at late times. The spectral energy distribution shape, probed by the ratio (LBB/LX) between the UV/optical and X-ray, shows a wide range ofLBB/LX∈ (0.5, 3000) at early times and converges to disklike values ofLBB/LX∈ (0.5, 10) at late times. We estimate the fraction of optically discovered TDEs withLX≥ 1042erg s−1to be at least 40% and show that X-ray loudness is independent of black hole mass. We argue that distinct disk formation timescales are unlikely to be able to explain the diverse range of X-ray evolution. We combine our sample with X-ray-discovered ones to construct an X-ray luminosity function, best fit by a broken power law, with a break atLX≈ 1044erg s−1. We show that there is no dichotomy between optically and X-ray-selected TDEs; instead, there is a continuum of early-timeLBB/LX, at least as wide asLBB/LX∈ (0.1, 3000), with optical/X-ray surveys selecting preferentially, but not exclusively, from the higher/lower end of the distribution. Our findings are consistent with unification models for the overall TDE population.
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A Luminous Dust-obscured Tidal Disruption Event Candidate in a Star-forming Galaxy at 42 Mpc
Abstract While the vast majority of tidal disruption events (TDEs) have been identified by wide-field sky surveys in the optical and X-ray bands, recent studies indicate that a considerable fraction of TDEs may be dust obscured and thus preferentially detected in the infrared (IR) wave bands. In this Letter, we present the discovery of a luminous mid-IR nuclear flare (termed WTP14adbjsh), identified in a systematic transient search of archival images from the NEOWISE mid-IR survey. The source reached a peak luminosity ofL≃ 1043erg s−1at 4.6μm in 2015 before fading in the IR with a TDE-likeF∝t−5/3decline, radiating a total of more than 3 × 1051erg in the last 7 yr. The transient event took place in the nearby galaxy NGC 7392, at a distance of around 42 Mpc; yet, no optical or X-ray flare is detected. We interpret the transient as the nearest TDE candidate detected in the last decade, which was missed at other wavelengths due to dust obscuration, hinting at the existence of TDEs that have been historically overlooked. Unlike most previously detected TDEs, the transient was discovered in a star-forming galaxy, corroborating earlier suggestions that dust obscuration suppresses significantly the detection of TDEs in these environments. Our results demonstrate that the study of IR-detected TDEs is critical in order to obtain a complete understanding of the physics of TDEs and to conclude whether TDEs occur preferentially in a particular class of galaxies.
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- Award ID(s):
- 1828470
- PAR ID:
- 10495333
- Publisher / Repository:
- The Astrophysical Journal Letters
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 948
- Issue:
- 1
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L5
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/2041-8213/acc02f
