Non-Steady State Accretion Disks in X-Ray Novae: Outburst Models for Nova Monocerotis 1975 and Nova Muscae 1991

TL;DR

This paper models the outbursts of two X-ray novae using a new time-dependent accretion disk model, deriving key parameters and comparing results with observed light curves to understand disk viscosity.

Contribution

It introduces a novel solution for a diffusion equation in non-steady-state accretion disks and applies it to real X-ray nova outbursts, estimating viscosity parameters.

Findings

Estimated turbulence parameter alpha: 0.2-0.4 for A 0620-00

Estimated turbulence parameter alpha: 0.45-0.65 for GS 1124-683

Derived distances to systems as functions of compact object masses

Abstract

We fit outbursts of two X-ray novae (Nova Monocerotis 1975=A0620-00 and Nova Muscae GS 1991=1124-683) using a time-dependent accretion disk model. The model is based on a new solution for a diffusion-type equation for the non-steady-state accretion and describes the evolution of a viscous alpha-disk in a binary system after the peak of an outburst, when matter in the disk is totally ionized. The accretion rate in the disk decreases according to a power law. We derive formulas for the accretion rate and effective temperature of the disk. The model has three free input parameters: the mass of the central object M, the turbulence parameter alpha, and the normalization parameter delta t. Results of the modeling are compared with the observed X-ray and optical B and V light curves. The resulting estimates for the turbulence parameter $\alpha$ are similar: 0.2-0.4 for A 0620-00 and 0.45-0.65 for GS 1124-683, suggesting a similar nature for the viscosity in the accretion disks around the compact objects in these sources. We also derive the distances to these systems as functions of the masses of their compact objects.