Spectral evolution of 4U 1543-47 in 2002

The observed dM(t)/dt is obtained from spectral modelling of the archival Proportional Counter Array aboard the RXTE observatory (RXTE/PCA) data. Different scenarios of disc decay evolution are possible depending on a degree of self-irradiation of the disc by the emission from its centre.

If the self-irradiation, which is parametrized by factor C_irr_, had been as high as ~5x10^-3^, then the disc would have been completely ionized up to the tidal radius and the short time of the decay would have required the turbulent parameter {alpha}~3. We find that the shape of the \dot M(t) curve is much better explained in a model with a shrinking high-viscosity zone. If C_irr_~(2-3)x10^-4^, the resulting {alpha} lie in the interval 0.5-1.5 for the black hole masses in the range 6-10M_{sun}_, while the radius of the ionized disc is variable and controlled by irradiation.