Evolution of relativistic thin discs with a finite ISCO stress: II. Late time behaviour

Abstract

We present solutions to the relativistic thin disc evolutionary equation using a modified description of the mean fluid flow within the disc. The model takes into account the effects of sub-circular velocities in the innermost disc regions, and resolves otherwise unsustainable behaviour present in simple finite ISCO stress disc models. We show that the behaviour of a relativistic thin disc evolving with a finite ISCO stress is comprised of three distinct stages which join the ordinarily distinct finite and vanishing ISCO stress solutions into a fully continuous model parameterisation. The most important prediction of our model is the existence of an intermediate stage of "stalled accretion", controlled by a single dimensionless parameter. The hallmarks of this evolutionary phase appear to have been seen in GRMHD simulations as well as in the late time X-ray observations of tidal disruption events, but dedicated simulations and extended observations are needed for a deeper understanding.

arXiv comment10 pages, 8 figures. Accepted for publication in MNRAS

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• Accretion Disc Winds in Tidal Disruption Events: Ultraviolet Spectral Lines as Orientation Indicators
• A maximum X-ray luminosity scale of disc-dominated tidal disruption events
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• Asymptotic Green's function solutions of the general relativistic thin disc equations
• Wind-mediated Eddington-limited emission in a $10^4{M}_{\odot }$ Black Hole Tidal Disruption Event