MG14 - Talk detail

Back to previous page

 Participant

Institution

Session

Accepted

Order

Time

Talk

Title

Abstract

In the present work, we study the properties of standing and dissipative accretion shocks around a Kerr black hole. We consider accretion flows around a stellar-mass black holes which emit hard X-rays from the post-shock region, also known as Compton cloud, located close to the inner edge of the disc. The radiative loss primarily comes from the thermal and kinetic energy of the flow during its pre-shock to post-shock transition phase and takes place via Comptonization process. To explain the temporal variation of this radiative loss, we study the dynamical properties of the dissipative shocks as well as the standing shocks in a self-consistent way and compare the results. We quantitatively show how the energy loss at the shock affects the location of the shock itself around a rotating black hole. We find that for a suitable range of input parameters, the upper limit of the maximum release of energy at shock could be close enough to the total available energy. However, as the energy remove is significant, shock moves forward towards the black hole. We also compute the region of the parameter space (Energy vs. Angular momentum) and find that the effective area of parameter space is enhanced significantly as the dissipation is increased. The implication of this could be profound in studying the QPOs observed in several black hole candidates, such as XTE J1550−564 and GRO J1655−40, during their outbursts. The QPOs evolve rapidly and the frequency changes from several mHz to a few tens of Hz in its rising phase. This could be explained with the help of dissipative shock oscillation as the size of the post-shock region varies according to the energy released from it.

Pdf file

Session

Accepted

Order

Time

Talk

Title

Abstract

In the present study, we investigate the possibilities of shocks in the accretion/wind flows. For the constant ultra-relativistic adiabatic index $\!\gamma (=\!\frac{4}{3})$, shocks are possible because of the presence of the two saddle type sonic points in the flow. However, in the case accretion flows matter remains cool (non-relativistic i.e., $\gamma=\frac{5}{3}$) at the outer boundary and becomes very hot (extreme relativistic and $\gamma=\frac{4}{3}$) at the inner edge, the smooth variation of from $\frac{5}{3} \leq \gamma \leq \frac{4}{3}$ (outer to inner) needs to be taken into account while solving the hydrodynamic equations. In our recent study, we find that except for the region very nearby the compact object, does not change significantly from its non-relativistic value ( which was opposite to the previous study ) and therefore, the EOS mostly remains non-relativistic in nature. Employing this relativistic equation of state(EOS) (Synge 1957) in which the adiabatic index varies ( $\frac{5}{3} \to \frac{4}{3}$ ) from the non relativistic to relativistic regime with temperature we notice that number of the saddle type sonic point reduces to one indicating that the formation of shocks in the flow becomes unlikely.

Pdf file

Back to previous page