We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter, PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (E) and specific angular momentum (λ) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole (a k ) plays an important role in deciding the outflow rate Rṁ (ratio of mass flux of outflow and inflow), in particular, Rṁ is directly correlated with a k for the same set of inflow parameters. It is found that a large range of the inflow parameters allows global accretion-ejection solutions and the effective area of the parameter space (E, λ) with and without outflow decreases with black hole spin (a k ). We compute the maximum outflow rate (R maẋ m ) as function of black hole spin (a k ) and observe that R maẋ m weakly depends on a k that lies in the range ∼ 10% − 18% of the inflow rate for the adiabatic index (γ) with 1.5 γ 4/3. We present the observational implication of our approach while studying the steady/persistent Jet activities based on the accretion states of black holes. We discuss that our formalism seems to have the potential to explain the observed Jet kinetic power for several Galactic Black Hole sources (GBHs) and Active Galactic Nuclei (AGNs).

We study the properties of the dissipative accretion flow around rotating black holes in presence of mass loss. We obtain the complete set of global inflow-outflow solutions in the steady state by solving the underlying conservation equations selfconsistently. We observe that global inflow-outflow solutions are not the isolated solution, instead such solutions are possible for wide range of inflow parameters. Accordingly, we identify the boundary of the parameter space for outflows, spanned by the angular momentum (λ in ) and the energy (E in ) at the inner sonic point (x in ), as function of the dissipation parameters and find that parameter space gradually shrinks with the increase of dissipation rates. Further, we examine the properties of the outflow rate Rṁ (defined as the ratio of outflow to inflow mass flux) and ascertain that dissipative processes play the decisive role in determining the outflow rates. We calculate the limits on the maximum outflow rate (R maẋ m ) in terms of viscosity parameter (α) as well as black hole spin (a k ) and obtain the limiting range as 3% R maẋ m 19%. Moreover, we calculate the viable range of α that admits the coupled inflow-outflow solutions and find that α 0.25 for Rṁ = 0. Finally, we discuss the observational implication of our formalism to infer the spin of the black holes. Towards this, considering the highest observed QPO frequency of black hole source GRO J1655-40 (∼ 450 Hz), we constrain the spin value of the source as a k 0.57.

We examine the effects of magnetic field on low angular momentum flows with standing shock around black holes in two dimensions. The magnetic field brings change in behavior and location of the shock which results in regularly or chaotically oscillating phenomena of the flow. Adopting fiducial parameters like specific angular momentum, specific energy and magnetic field strength for the flow around Sgr A*, we find that the shock moves back and forth in the range 60 -170R g , irregularly recurring with a time-scale of ∼ 5 days with an accompanying more rapid small modulation with a period of 25 hrs without fading, where R g is the Schwarzschild radius. The time variability associated with two different periods is attributed to the oscillating outer strong shock, together with another rapidly oscillating inner weak shock.As a consequence of the variable shock location, the luminosities vary roughly by more than a factor of 3. The time-dependent behaviors of the flow are well compatible with luminous flares with a frequency of ∼ one per day and bright flares occurring every ∼ 5 -10 days in the latest observations by Chandra, Swift and XMM-Newton monitoring of Sgr A*.

We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (∼ 166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3−150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasiperiodic Oscillation (QPO) frequencies using the twocomponent advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (ṁ d ), sub-Keplerian accretion rate (ṁ h ), shock location (r s ) and black hole mass (M bh ) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as L obs jet ∼ 3 − 6 × 10 37 erg s −1 during one of the observed radio flares which indicates that jet power corresponds to 8 − 16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (∼ 14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2 − 7.9M ⊙ with 90% confidence.

We study two-dimensional low angular momentum flow around a black hole using the resistive magnetohydrodynamic module of PLUTO code. Simulations have been performed for the flows with parameters of specific angular momentum, specific energy and magnetic field which may be expected for the flow around Sgr A*. For flows with lower resistivity η = 10−6 and 0.01, the luminosity and shock location on the equator vary quasi-periodically. The power density spectra of luminosity variation show peak frequencies which correspond to the periods of 5 × 105, 1.4 × 105 and 5 × 104 s. These quasi-periodic oscillations (QPOs) occur due to interaction between the outer oscillating standing shock and the inner weak shocks occurring at the innermost hot blob. While for cases with higher resistivity η = 0.1 and 1.0, the high resistivity considerably suppresses the magnetic activity such as MHD turbulence and the flows tend to be steady and symmetric with respect to the equator. The steady standing shock is formed more outward compared with the hydrodynamical flow. The low angular momentum flow model with the above flow parameters and with low resistivity has a possibility to explain long-term flares of Sgr A* with frequencies ∼ one per day and ∼ 5 – 10 days in the latest observations by Chandra, Swift and XMM-Newton monitoring of Sgr A*.