Fainter harder brighter softer: a correlation between αox, X-ray spectral state, and Eddington ratio in tidal disruption events. (22nd May 2020)

• Record Type: Journal Article
• Authors: Wevers, Thomas
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 497:Number 1(2020)
• Page Start: L1
• Page End: L6
• Publication Date: 2020-05-22
• Subjects: accretion, accretion disc -- black hole physics -- galaxies: active -- galaxies: nuclei -- transients: tidal disruption events; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slaa097
• Languages: English
• ISSNs: 1745-3933

Abstract

Abstract: We explore the accretion states of tidal disruption events (TDEs) using a sample of seven X-ray bright sources. To this end, we estimate the relative contribution of the disc and corona to the observed X-ray emission through spectral modelling, and assess the X-ray brightness (through αox, L $_{2\ \rm keV}$, and f Edd, X ) as a function of the Eddington ratio. We report strong positive correlations between αox and f Edd, bol ; f Edd, X and f Edd, UV ; and an anticorrelation for L $_{2\ \rm keV}$ and f Edd, UV . TDEs at high f Edd, bol have thermal dominated X-ray spectra and high (soft) αox, whereas those at low f Edd, bol show a significant power-law contribution and low (hard) αox . Similar to X-ray binaries and active galactic nuclei, the transition between X-ray spectral states occurs around f Edd, bol ≈ 0.03, although the uncertainty is large due to the small sample size. Our results suggest that X-ray surveys are more likely to discover TDEs at low f Edd, bol, whereas optical surveys are more sensitive to TDEs at high Eddington ratios. The X-ray and optical selected TDEs have different UV and X-ray properties, which should be taken into account when deriving rates, luminosity, and black hole mass functions.