We report the results of AstroSat observations of GRS 1915+105 obtained using 100 ks guaranteed-time (GT) during the soft state. The Color-Color Diagram (CCD) indicates a variability class of δ with the detection of High Frequency QPO (HFQPO) in the power density spectra (PDS). The HFQPO is seen to vary in the frequency range of 67.96 − 70.62 Hz with percentage rms ∼0.83 − 1.90 % and significance varying from 1.63 − 7.75. The energy dependent power spectra show that the HFQPO features are dominant only in 6 − 25 keV energy band. The broadband energy spectra (0.7 − 50 keV) of SXT (Soft X-ray Telescope) and LAXPC (Large Area X-ray Proportional Counter) modelled with nthComp and powerlaw imply that the source has an extended corona in addition to a compact ‘Comptonizing corona’ that produces high energy emission and exhibits HFQPOs. The broadband spectral modelling indicates that the source spectra are well described by thermal Comptonization with electron temperature (kTe) of 2.07 − 2.43 keV and photon-index (Γnth) between 1.73 − 2.45 with an additional powerlaw component of photon-index (ΓPL) between 2.94 − 3.28. The norm of nthComp component is high (∼8) during the presence of strong HFQPO and low (∼3) during the absence of HFQPO. Further, we model the energy spectra with the kerrbb model to estimate the accretion rate, mass and spin of the source. Our findings indicate that the source accretes at super-Eddington rate of $1.17-1.31~ \dot{M}_{\rm Edd}$. Moreover, we find the mass and spin of the source as 12.44 − 13.09 M⊙ and 0.990 − 0.997 with $90\%$ confidence suggesting that GRS 1915+105 is a maximally rotating stellar mass X-ray binary black hole source.
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.
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