A systematic analysis of the X-ray emission in optically selected tidal disruption events: observational evidence for the unification of the optically and X-ray selected populations

2023/08/24 by Muryel Guolo, Guolo, Muryel, Suvi Gezari +11 · 15 citations
Biochemistry, Genetics and Molecular Biology · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics of Galaxies (astro-ph.GA) #Earthquake Detection and Analysis #FOS: Physical sciences #Geomagnetism and Paleomagnetism Studies #High Energy Astrophysical Phenomena (astro-ph.HE) #Solar and Space Plasma Dynamics

paper · pdf · doi:10.48550/arxiv.2308.13019

openalex publication_date 2023/08/24 · openalex created_date 2023/08/29 · openalex updated_date 2026/07/28

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 (L_{\rm BB}/L_{\rm X}) between the UV/optical and X-ray, shows a wide range L_{\rm BB}/L_{\rm X} ∈ (0.5, 3000) at early-times, and converges to disk-like values L_{\rm BB}/L_{\rm X} ∈ (0.5, 10) at late-times. We estimate the fraction of optically discovered TDEs with L_{\rm X} ≥ 10⁴²~\rmerg~\rms^-1 to be at least 40%, and show that X-ray loudness is independent of black hole mass. We argue that distinct disk formation time scales are unlikely to fully explain the diverse range of X-ray evolutions. We combine our sample with X-ray discovered ones to construct an X-ray luminosity function, best fitted by a broken power-law, with a break at L_{\rm X} ≈ 10⁴⁴~\rmerg~\rms^-1 . We show that there is no dichotomy between optically and X-ray selected TDEs, instead there is a continuum of early time L_{\rm BB}/L_{\rm X}, at least as wide as L_{\rm BB}/L_{\rm X} ∈ (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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