Estimation of alpha-viscosity coefficient from observations of nonstationary disk accretion

TL;DR

This paper models the optical and X-ray outbursts in a high-mass X-ray binary system using a nonstationary accretion disk framework, estimating the alpha-viscosity parameter from observational data.

Contribution

It introduces a quantitative model linking disk viscosity to observed outburst delays, providing an estimate of the alpha-viscosity coefficient from real observations.

Findings

Estimated alpha-viscosity coefficient as 0.1-0.3

Explained the delay between optical and X-ray peaks

Linked disk dynamics to observed luminosity variations

Abstract

The optical behaviour of the Be star in the high mass X-ray transient A0535+26/HDE245770 shows that at the periastron typically there is an enhancement in the luminosity of order 0.05 to few tenths mag, and the X- ray outburst happens about 8 days after the periastron. We construct a quantitative model of this event, basing on a nonstationary accretion disk behavior, connected with a high ellipticity of the orbital motion. We explain the observed time delay between the peaks of the optical and X-ray outbursts in this system by the time of radial motion of a matter in the accretion disk, after increase of the mass flux in the vicinity of a periastral point in the binary. This time is determined by the turbulent viscosity, with the parameter $ \alpha=0.1-0.3$, estimated from the comparison of the model with observational data