Abstract
ABSTRACT We comprehensively model the X-ray luminosity emergent from time-dependent relativistic accretion discs, developing analytical models of the X-ray luminosity of thermal disc systems as a function of black hole mass M, disc mass Md, and disc α-parameter. The X-ray properties of these solutions will be directly relevant for understanding tidal disruption event (TDE) observations. We demonstrate an extremely strong suppression of thermal X-ray luminosity from large mass black holes, LX ∼ exp (− m7/6), where m is a dimensionless mass, roughly the black hole mass in unity of 106M⊙. This strong suppression results in upper observable black hole mass limits, which we demonstrate to be of order Mlim ≃ 3 × 107M⊙, above which thermal X-ray emission will not be observable. This upper observable black hole mass limit is a function of the remaining disc parameters, and the full dependence can be described analytically (equation 82). We demonstrate that the current population of observed X-ray TDEs is indeed consistent with an upper black hole mass limit of order M ∼ 107M⊙, consistent with our analysis.
Highlights
There is good observational and theoretical evidence that the dominant emission components of many tidal disruption event (TDE) light curves come from evolving thin discs
14li was detected at X-ray energies for almost 1000 days (Bright et al 2018). This light curve was well-described by thermal emission from a stable accretion disc (Mummery & Balbus 2020a), despite having an Eddington ratio of ∼ 0.85, which would be formally unstable by way of the usual α-disc modelling
When a relativistic accretion disc is observed at an inclined angle, substantial Doppler blue shifting of photons emitted from the inner disc material moving with large line-of-sight velocities can overcome the gravitational red-shift
Summary
There is good observational and theoretical evidence that the dominant emission components of many tidal disruption event (TDE) light curves come from evolving thin discs (van Velzen et al 2019, Mummery & Balbus 2020a, b). Late time UV observations of six well-observed TDEs show transitions to disc-dominated states after ∼ 100 days (van Velzen et al 2019), and the spectra of a large sample of X-ray TDEs show properties which are analogous to the high-luminosity spectrally-soft accretion state of X-ray binaries (e.g., Saxton et al 2012; Miller et al 2015; Lin et al 2015; Holoien et al 2016a; Gezari et al 2017; Wevers et al 2019b; Jonker et al 2020, Wen et al 2020) Motivated by these findings, the authors recently developed and applied time-dependent relativistic thin disc theory (Balbus 2017, Balbus & Mummery 2018) to the light curves of the well-observed TDE ASASSN-14li (Holoein et al 2016a, Mummery & Balbus 2020a).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
