Location: Seminar room, Prague

X-ray binaries hosting compact objects exhibit often characteristic variability patterns in their lightcurves, attributed to thermoviscous instabilities within their accretion disks. In particular, the short-term limit-cycle oscillations are believed to arise from radiation pressure induced (RPI) instabilities, operating in the inner regions of the disk, where radiation pressure is dominant. A model investigating such RPIs in accretion disks was developed by Janiuk et al. (2002) and has since been applied to several black hole X-ray binaries. In the talk, I plan to elaborate on our efforts to study how irradiation from the central source affects the evolution of an unstable disk around a black-hole, within the framework of the disk-instability model. In recent years, irradiation has been recognized as an important factor in the disk evolution e.g. by Dubus et al (1999). The central compact region can be a hot corona in case of black hole accretors, or a hot boundary layer, between the disk and the stellar surface, in case of accreting neutron stars. For our study, we employ the code GLADIS, which computes a 1D, vertically averaged, global hydrodynamical model of the disk. We include the extra flux in our energy balance equation, whose net contribution to the cells depends strongly on the geometry of the system. We then explore different types of oscillations an irradiated, unstable disk can produce, and use them to model the “heartbeat” oscillations observed in the X-ray binary 4U 1630-47 by Fan et al. (2025). I’ll attempt to briefly present our results, showing how irradiation significantly changes the evolution of the disk and what more physics can we include in our models.

Location: ASU-Praha, Spořilov