Indranil Chattopadhyay

Computation of outflow rates from accretion disks around black holes

We self-consistently estimate the outflow rate from the accretion rates of an accretion disk around a black hole in which both the Keplerian and the sub-Keplerian matter flows simultaneously. While Keplerian matter supplies soft-photons, hot sub-Keplerian matter supplies thermal electrons. The temperature of the hot electrons is decided by the degree of inverse Comptonization of the soft photons. If we consider only thermally-driven flows from the centrifugal pressure-supported boundary layer around a black hole, we find that when the thermal electrons are cooled down, either because of the absence of the boundary layer (low compression ratio), or when the surface of the boundary layer is formed very far away, the outflow rate is negligible. For an intermediate size of this boundary layer the outflow rate is maximal. Since the temperature of the thermal electrons also decides the spectral state of a black hole, we predict that the outflow rate should be directly related to the spectral state.

STANDING SHOCKS AROUND BLACK HOLES: AN ANALYTICAL STUDY

We compute locations of sonic points and standing shock waves in a thin, axisymmetric, adiabatic flow around a Schwarzschild black hole. We use a completely analytical method to achieve our goal. Our results are compared with those obtained numerically, and good agreement is seen. Our results prove the existence of shocks in centrifugal pressure-dominated flows. We indicate how our results can be used to obtain spectral properties and frequencies of shock oscillations, which may be directly related to the quasi-periodic oscillations of hard X-rays.

Radiatively driven plasma jets around compact objects

Matter accreting on to black holes may develop shocks due to the centrifugal barrier. Some of the inflowing matter in the post-shock flow is deflected along the axis in the form of jets. Post-shock flow which behaves likea Compton cloud has hot electrons emitting high-energy photons. We study the effect of these hot photons on the outflowing matter. Radiation from this region could accelerate the outflowing matter, but radiation pressure should also slow it down. We show that the radiation drag restricts the flow from attaining a very high velocity. We introduce the concept of an equilibrium velocity (u e q ∼ 0.5c), which sets the upper limit of the terminal velocity achieved by a cold plasma due to radiation deposition force in the absence of gravity. If the injection energy is E i n , then we find that the terminal velocity v ∞ satisfies a relation u 2 ∞ ≤ u2 e q + 2E i n .

EFFECTS OF THE COMPOSITION ON TRANSONIC PROPERTIES OF ACCRETION FLOWS AROUND BLACK HOLES

We study the properties of a steady, multi-species, low angular momentum accretion flow around a Schwarzschild black hole. Each species is described by a relativistic equation of state. We find that the transonic properties depend strongly on the composition of the flow. We find that an electron-positron pair plasma is the least relativistic one. This flow produces only one sonic point very close to the event horizon and does not show multiple critical points for any angular momentum or energy. When the baryons are present, the number of critical points depend on the specific energy content. Since the number of critical points decide whether the flow will have nonlinearities or shock waves, our results imply that whether standing shocks will form or not depends on the flow composition. Thus, for instance, a pure electron-positron pair plasma will never undergo a shock transition, while mixing it with some baryons (common in outflows and jets, for example) as in a completely ionized gas, will have shocks. We study in detail how the baryon loading affects the shock properties and discuss the implications in astrophysical observations.

General relativistic study of astrophysical jets with internal shocks

We explore the possibility of formation of steady internal shocks in jets around black holes. We consider a fluid described by a relativistic equation of state, flowing about the axis of symmetry (

INVESTIGATION OF RADIATIVE OUTFLOWS AROUND COMPACT OBJECTS

theta=0

A COMPARATIVE STUDY OF BONDI-TYPE AND RADIATIVE OUTFLOWS AROUND COMPACT OBJECTS

) in a Schwarzschild metric. We use two models for the jet geometry, (i) a conical geometry and (ii) a geometry with non-conical cross-section. Jet with conical geometry is smooth flow. While the jet with non-conical cross section undergoes multiple sonic point and even standing shock. The jet shock becomes stronger, as the shock location is situated further from the central black hole. Jets with very high energy and very low energy do not harbour shocks, but jets with intermediate energies do harbour shocks. One advantage of these shocks, as opposed to shocks mediated by external medium is that, these shocks have no effect on the jet terminal speed, but may act as possible sites for particle acceleration. Typically, a jet with energy

Radiatively driven relativistic jets in Schwarzschild space-time

1.8~c^2

Mass loss from a viscous accretion disc in presence of cooling

, will achieve a terminal speed of

On radiative acceleration of jets and outflows from advective disks

v_infty=0.813c