The ionization instability driven outbursts in 4U 1630-472

Patrycja Bagińska, Agata Różańska, Bożena Czerny and Agnieszka Janiuk

We show that two outbursts observed in X-ray lightcurves of the transient source, 4U 1630-472, can be well explained by an accretion disk instability mechanism. The instability is caused by hydrogen partial ionisation in the outer part of the disk. When the unstable front moves toward the central object, classical outburst appears with duration from 30 up to 400 days.The shape of an outburst can be very regular like fast rise exponential decay profile (FRED) very characteristic for ionisation instability mechanism or irregular suggesting that, beside FRED, additional flickering occurs. We use the model which predicts time dependent evolution of ionisation instability in an accretion disk around black hole, assuming viscosity parameter to be proportional to the gas pressure. As a result, modelled lightcurves fit to the observed RXTE lightcurves, indicating that disk instability occurs in this source. For both outbursts we obtain the same black hole mass of the compact object M = 4 M_Sun.

Proceedings of the Polish Astronomical Society, vol. 3, 154-157 (2016)

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