Modeling of non-stationary accretion disks in X-ray novae A 0620-00 and GRS 1124-68 during outburst

TL;DR

This paper models the non-stationary accretion disks in X-ray novae during outbursts, incorporating relativistic effects and self-irradiation, to constrain black hole spin and disk viscosity parameters.

Contribution

It introduces an analytic model of viscous evolution of truncated accretion disks that accounts for relativistic effects and disk irradiation, applied to specific X-ray novae.

Findings

Constraints on black hole Kerr parameters: 0.3-0.6 for A 0620-00 and ≤0.4 for GRS 1124-68.

Estimated viscosity parameter : 0.7-0.95 for A 0620-00 and 0.55-0.75 for GRS 1124-68.

Disks are thicker than theoretical predictions by a factor of 1.5-2.

Abstract

We address the task of modeling soft X-ray and optical light curves of X-ray novae in the high/soft state. The analytic model of viscous evolution of an externally truncated accretion \alpha-disk is used. Relativistic effects near a Kerr black hole and self-irradiation of an accretion disk are taken into account. The model is applied to the outbursts of X-ray nova Monocerotis 1975 (A 0620-00) and X-ray nova Muscae 1991 (GRS 1124-68). Comparison of observational data with the model yields constraints on the angular momentum (the Kerr parameter) of the black holes in A 0620-00 and GRS 1124-68: 0.3-0.6 and \leq 0.4, and on the viscosity parameter \alpha of the disks: 0.7-0.95 and 0.55-0.75. We also conclude that the accretion disks should have an effective geometrical thickness 1.5-2 times greater than the theoretical value of the distance between the photometric layers.