MG11 
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Numerical Studies of the Standing and Oscillating Shocks in Accretion Flows in a pseudo-Kerr Geometry

When matter with a constant angular momentum accretes on a black hole, the tug-of-war between the inward pointing gravitational force and the outward pointing cenrifugal force causes the formation of standing and oscillating shock waves. We use a pseudo-Newtonian approach (which we device) in which Newtonian equations are used around an object having such a potential that the geometry external to it is similar to that around a Kerr black hole. We present theoretical work based on sonic point analysis and divide the entire parameter space spanned by energy and angular momentum in terms of flow topologies. We carry out numerical simulations using SPH and show that these shocks really form. Some of them could be oscillatory and radiations from them could explain the quasi-periodic oscillations observed in black hole candidates.

Standing Shocks in Pseudo-Kerr Geometry

We devise a pseudo-Kerr potential which is such that a particle moving in this potential behaves as though it is moving around a Kerr black hole. Our potential is valid for off the equatorial plane and gives satisfactory results for -1<a<0.8. We apply this to study standing shocks in Kerr geometry in accretion and winds. We find that as the rotation parameter is increased the shock forms closer to the black hole. We also perform numerical simulations of these shock waves with cooling taken into account and show that high frequency QPOs may be explained by shock-oscillations around a Kerr black hole.

Anlytical and numerical studies of accretion shocks in Pseudo-Kerr Geometry

We devise a pseudo-Kerr potential which is such that a particle moving in this potential behaves as though it is moving around a Kerr black hole. Our potential is valid for off the equatorial plane and gives satisfactory results for -1<a<0.8. We apply this to study standing shocks in Kerr geometry in accretion and winds. We find that as the rotation parameter is increased the shock forms closer to the black hole. We also perform numerical simulations of these shock waves with cooling taken into account and show that high frequency QPOs may be explained by shock-oscillations around a Kerr black hole.