Determination of the turbulent parameter in the accretion disks: effects of self-irradiation in 4U 1543-47 during the 2002 outburst

G. V. Lipunova, K. L. Malanchev

Published 2016-10-05Version 1

The accretion disk around black hole in 4U 1543-47, a binary system with the orbital period of 1.116 day, can have the size of about $4 \mathrm{R}_\odot$. An outburst of 4U 1543-47 in 2002 has a characteristic exponential decay time of about 15 days. Such fast decay cannot be explained by the viscous evolution in the whole disk, and the evolution of the inner hot disk with changing size should be considered. Accretion rate evolution of this burst is obtained from spectral modelling of the archival RXTE/PCA data. Estimates on $\alpha$ are derived by fitting observed $\dot M(t)$ to the numerical results of the code Freddi for a range of black hole masses and Kerr parameters. If the self-irradiation of the disk by the emission from its center, which is parametrized by factor $C_\mathrm{irr}$, was as high as suggested for other X-ray transients then the disk was completely ionized and the short time of the decay required huge $\alpha$. Different scenarios are possible depending on the degree of irradiation. If irradiation factor $C_\mathrm{irr}$ was about $5\times10^{-4}$, a decade lower than suggested for X-ray transients, the disk could be viscously evolving with the hot zone size controlled by irradiation. For even weaker irradiation, the burst decline proceeded as in normal outbursts of dwarf novae and $\alpha_\mathrm{hot}\sim 0.1-0.3$. The analytic approximations are derived to estimate $\alpha$ in X-ray novae using $\dot M(t)$. Resulting $\alpha$ can vary remarkably depending on the unknown black hole Kerr parameter and the self-irradiation degree.