Tidal disruption event discs are larger than they seem: removing systematic biases in TDE X-ray spectral modelling

Journal article

The physical sizes of tidal disruption event (TDE) accretion discs are regularly inferred, from modelling of the TDEs X-ray spectrum as a single-temperature blackbody, to be smaller than the plausible event horizons of the black holes which they occur around – a clearly unphysical result. In this Lltter, we demonstrate that the use of single-temperature blackbody functions results in the systematic underestimation of TDE accretion disc sizes by as much as an order of magnitude. In fact, the radial ‘size’ inferred from fitting a single-temperature blackbody to an observed accretion disc X-ray spectrum does not even positively correlate with the physical size of that accretion disc. We further demonstrate that the disc-observer inclination angle and absorption of X-ray photons may both lead to additional underestimation of the radial sizes of TDE discs, but by smaller factors. To rectify these issues, we present a new fitting function which accurately reproduces the size of an accretion disc from its 0.3−10 keV X-ray spectrum. Unlike traditional approaches, this new fitting function does not assume that the accretion disc has reached a steady-state configuration, an assumption which is unlikely to be satisfied by most TDEs.

Authors: Mummery, AP

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society: Letters
• Volume: 507
• Issue: 1
• Pages: L24-L28
• Publication date: 2021-07-30
• Acceptance date: 2021-07-22
• DOI: 10.1093/mnrasl/slab088
• EISSN: 1745-3933
• ISSN: 1745-3925
• Language: English
• Keywords: FFR