Microquasar IGR J-17091-3624 – simulations of the unstable accretion disk

Microquasar IGR-J-17091-3624 is an object, which is emitting the X-ray outbursts with period between 5 and 70 seconds.The plot below presents its X-ray lightcurve, where the characteristic pattern of oscillations (‘heartbeat’) is seen. (Data from RXTE satellite. Reduction: Wojtek Kowalski).


Using our own hydrodynamical code GLADIS (GLobal Accretion Disk InStability) we created a model which simulates the behaviour of an accretion disk around IGR-J-17091. Code GLADIS is an 1,5 – dimensional hydrodynamical code, which models a geometrically thin, Keplerian alpha-disk with the energy dissipation rate that scales with the total (including radiation) pressure. The disk is surrounding a central object, i.e. a black hole, which attracts the matter with a force described using the pseudo-Newtonian Paczyński-Wiita potential.


In the plots above, and in the animations we show the changes of the temperature and density of the accretion disk during its outbursts. They are produced due to the thermal-viscous instability because of a dominant radiation pressure. Coloured contour presents the profile of the disk in a log-scale, in the r-z plane. The distance is expressed in the Schwarzschild radius units. The calculation was carried for the mass of black hole equal to 6 solar mass, accretion rate 0.1 Eddington rate and the viscosity parameter alpha equal to 0.1. Also, a wind, with dimensionless strength coefficient A=15, was assumed, and it takes away a part of energy flux dissipated locally in the disk. The presence of this wind is important to regulate the amplitudes of disk oscillations, to the level that reproduce the observed X-ray variability. Is has been also confirmed by the spectroscopic observations of the microquasar IGR J17091 taken by Chandra satellite.

Click on the movie to see how the accretion disk oscillates. (Simulations with code GLADIS. Author: Mikołaj Grzędzielski).


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