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

Andrew Mummery
2021 Monthly Notices of the Royal Astronomical Society: Letters  
The physical sizes of 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 Letter 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
more » ... tting 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.
doi:10.1093/mnrasl/slab088 fatcat:m7lvyjok55a2rfexwead3afewq