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

Monthly Notices of the Royal Astronomical Society. 2017. Vol. 468. No. 4. P. 4735–4747.

Lipunova G. V., Malanchev K. L.

We investigate the viscous evolution of the accretion disc in 4U 1543-47, a black hole binary system, during the first 30 d after the peak of the 2002 burst by comparing the observed and theoretical accretion rate evolution \dot{M}(t). The observed \dot{M}(t) 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 Cirr, had been as high as ˜5 × 10-3, 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 α ˜ 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 Cirr ≈ (2-3) × 10-4, the resulting α lie in the interval 0.5-1.5 for the black hole masses in the range 6-10 M⊙, while the radius of the ionized disc is variable and controlled by irradiation. For very weak irradiation, Cirr < 1.5 × 10-4, the burst decline develops as in normal outbursts of dwarf novae with α ˜ 0.08-0.32. The optical data indicate that Cirr in 4U 1543-47 (2002) was not greater than approximately (3-6) × 10-4. Generally, modelling of an X-ray nova burst allows one to estimate α that depends on the black hole parameters. We present the public 1D code freddi to model the viscous evolution of an accretion disc. Analytic approximations are derived to estimate α in X-ray novae using \dot{M}(t).

Keywords: астрофизика, black holes, двойные звезды, accretion disk, тесные двойные звезды, аккреция, аккреционные диски, accretion, binary star