Prototyping non-equilibrium viscous-timescale accretion theory using LMC X-3

TL;DR

This paper investigates the physical mechanisms behind variability in the accretion flows of LMC X-3, a black hole X-ray binary, highlighting the need for complex physics beyond standard models to explain observed patterns.

Contribution

It introduces a simplified yet broad approach to study various mechanisms affecting accretion variability, emphasizing the importance of physics beyond traditional models.

Findings

Additional physics like winds and irradiation are needed to explain variability.

Evaporation--condensation processes may influence accretion behavior.

Current models are limited and require refinement for better accuracy.

Abstract

Explaining variability observed in the accretion flows of black hole X-ray binary systems remains challenging, especially concerning timescales less than, or comparable to, the viscous timescale but much larger than the inner orbital period despite decades of research identifying numerous relevant physical mechanisms. We take a simplified but broad approach to study several mechanisms likely relevant to patterns of variability observed in the persistently high-soft Roche-lobe overflow system LMC X-3. Based on simple estimates and upper bounds, we find that physics beyond varying disk/corona bifurcation at the disk edge, Compton-heated winds, modulation of total supply rate via irradiation of the companion, and the likely extent of the partial hydrogen ionization instability is needed to explain the degree, and especially the pattern, of variability in LMC X-3 largely due to viscous dampening. We then show how evaporation--condensation may resolve or compound the problem given the uncertainties associated with this complex mechanism and our current implementation. We briefly mention our plans to resolve the question, refine and extend our model, and alternatives we have not yet explored.