arXiv subjects

Santabrata Das

Publications and source records attributed to Santabrata Das.

At least 55 records · Page 3Linked to original sources

arXiv2022

Study of general relativistic magnetohydrodynamic accretion flow around black holes

We present a novel approach to study the global structure of steady, axisymmetric, advective, geometrically thin, magnetohydrodynamic (MHD) accretion flow around black holes in full general relativity (GR). Considering ideal MHD conditions and relativistic equation of state (REoS), we solve the governing equations to obtain all possible smooth global accretion solutions. We examine the dynamical and thermodynamical properties of accreting matter in terms of the flow parameters, namely energy (${\cal E}$), angular momentum (${\cal L}$), and local magnetic fields. For a thin GRMHD flow, we observe that toroidal component ($b^ϕ$) of the magnetic fields generally dominates over radial component ($b^r$) at the disk equatorial plane. This evidently suggests that toroidal magnetic field indeed plays important role in regulating the disk dynamics. We further notice that the disk remains mostly gas pressure ($p_{\rm gas}$) dominated ($β= p_{\rm gas}/p_{\rm mag} > 1$, $p_{\rm mag}$ refers magnetic pressure) except at the near horizon region, where magnetic fields become dynamically important ($β\sim 1$). We observe that Maxwell stress is developed that eventually yields angular momentum transport inside the disk. Towards this, we calculate the viscosity parameter ($α$) that appears to be radially varying. In addition, we examine the underlying scaling relation between $α$ and $β$, which clearly distinguishes two domains coexisted along the radial extent of the disk. Finally, we discuss the utility of the present formalism in the realm of GRMHD simulation studies.

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arXiv2022

On the origin of core radio emissions from black hole sources in the realm of relativistic shocked accretion flow

We study the relativistic, inviscid, advective accretion flow around the black holes and investigate a key feature of the accretion flow, namely the shock waves. We observe that the shock-induced accretion solutions are prevalent and such solutions are commonly obtained for a wide range of the flow parameters, such as energy (${\cal E}$) and angular momentum ($λ$), around the black holes of spin value $0\le a_{\rm k} < 1$. When the shock is dissipative in nature, a part of the accretion energy is released through the upper and lower surfaces of the disc at the location of the shock transition. We find that the maximum accretion energies that can be extracted at the dissipative shock ($Δ{\cal E}^{\rm max}$) are $\sim 1\%$ and $\sim 4.4\%$ for Schwarzschild black holes ($a_{\rm k}\rightarrow 0$) and Kerr black holes ($a_{\rm k}\rightarrow 1$), respectively. Using $Δ{\cal E}^{\rm max}$, we compute the loss of kinetic power (equivalently shock luminosity, $L_{\rm shock}$) that is enabled to comply with the energy budget for generating jets/outflows from the jet base ($i.e.$, post-shock flow). We compare $L_{\rm shock}$ with the observed core radio luminosity ($L_R$) of black hole sources for a wide mass range spanning $10$ orders of magnitude with sub-Eddington accretion rate and perceive that the present formalism seems to be potentially viable to account $L_R$ of $16$ Galactic black hole X-ray binaries (BH-XRBs) and $2176$ active galactic nuclei (AGNs). We further aim to address the core radio luminosity of intermediate-mass black hole (IMBH) sources and indicate that the present model formalism perhaps adequate to explain core radio emission of IMBH sources in the sub-Eddington accretion limit.

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arXiv2022

Wide-band view of High Frequency QPOs of GRS 1915+105 in 'softer' variability classes observed with AstroSat

We present a comprehensive temporal and spectral analysis of the 'softer' variability classes ($i.e.$, $θ$, $β$, $δ$, $ρ$, $κ$, $ω$ and $γ$) of the source GRS 1915+105 observed by AstroSat during $2016-2021$ campaign. Wide-band ($3-60$ keV) timing studies reveal the detection of High Frequency Quasi-periodic Oscillations (HFQPOs) with frequency of $68.14-72.32$ Hz, significance of $2.75-11 σ$, and rms amplitude of $1.48-2.66\%$ in $δ$, $κ$, $ω$ and $γ$ variability classes. Energy dependent power spectra impart that HFQPOs are detected only in $6-25$ keV energy band and rms amplitude is found to increase ($1-8\%$) with energy. The dynamical power spectra of $κ$ and $ω$ classes demonstrate that HFQPOs seem to be correlated with high count rates. We observe that wide-band ($0.7-50$ keV) energy spectra can be described by the thermal Comptonization component (nthComp) with photon index ($Γ_{\rm nth}$) of $1.83-2.89$ along with an additional steep ($Γ_{\rm PL}\sim3$) powerlaw component. The electron temperature ($kT_e$) of $1.82 -3.66$ keV and optical depth ($τ$) of $2-14$ indicate the presence of a cool and optically thick corona. In addition, nthComp components ($1.97 \lesssim Γ_{\rm nth} \lesssim 2.44$, $1.06 \times 10^{-8} \lesssim F_{\rm nth} ~({\rm erg} {\rm ~cm}^{-2} {\rm ~s}^{-1}) \lesssim 4.46\times 10^{-8}$) are found to dominate in presence of HFQPOs. Overall, these findings infer that HFQPOs are possibly resulted due to the modulation of the 'Comptonizing corona'. Further, we find that the bolometric luminosity ($0.3-100$ keV) of the source lies within the sub-Eddington ($3-34\%$ $L_{\rm Edd}$) regime. Finally, we discuss and compare the obtained results in the context of existing models on HFQPOs.

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arXiv2021

Relativistic viscous accretion flow model for ULX sources: A case study for IC 342 X-1

In this letter, we develop a model formalism to study the structure of a relativistic, viscous, optically thin, advective accretion flow around a rotating black hole in presence of radiative coolings. We use this model to examine the physical parameters of the Ultra-luminous X-ray sources (ULXs), namely mass ($M_{\rm BH}$), spin ($a_{\rm k}$) and accretion rate (${\dot m}$), respectively. While doing this, we adopt a recently developed effective potential to mimic the spacetime geometry around the rotating black holes. We solve the governing equations to obtain the shock induced global accretion solutions in terms of ${\dot m}$ and viscosity parameter ($α$). Using shock properties, we compute the Quasi-periodic Oscillation (QPO) frequency ($ν_{\rm QPO}$) of the post-shock matter (equivalently post-shock corona, hereafter PSC) pragmatically, when the shock front exhibits Quasi-periodic variations. We also calculate the luminosity of the entire disc for these shock solutions. Employing our results, we find that the present formalism is potentially promising to account the observed $ν_{\rm QPO}$ and bolometric luminosity ($L_{\rm bol}$) of a well studied ULX source IC 342 X-1. Our findings further imply that the central source of IC 342 X-1 seems to be rapidly rotating and accretes matter at super-Eddington accretion rate provided IC 342 X-1 harbors a massive stellar mass black hole ($M_{\rm BH} < 100 M_\odot$) as indicated by the previous studies.

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arXiv2020

AstroSat view of GRS 1915+105 during the Soft State: Detection of HFQPOs and estimation of Mass and Spin

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 $\sim 0.83 - 1.90$ % 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 (kT$_{\rm e}$) of $2.07 - 2.43$ keV and photon-index ($Γ_{\rm nth}$) between $1.73-2.45$ with an additional powerlaw component of photon-index ($Γ_{\rm PL}$) between $2.94 - 3.28$. The norm of nthComp component is high ($\sim 8$) during the presence of strong HFQPO and low ($\sim 3$) 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 $12.44 - 13.09~M_{\odot}$ 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.

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arXiv2020

Study of relativistic accretion flow in Kerr-Taub-NUT spacetime

We study the properties of the relativistic, steady, axisymmetric, low angular momentum, inviscid, advective, geometrically thin accretion flow in a Kerr-Taub-NUT (KTN) spacetime which is characterized by the Kerr parameter ($a_{\rm k}$) and NUT parameter ($n$). Depending on $a_{\rm k}$ and $n$ values, KTN spacetime represents either a black or a naked singularity. We solve the governing equations that describe the relativistic accretion flow in KTN spacetime and obtain all possible global transonic accretion solutions around KTN black hole in terms of the energy $({\cal E})$ and angular momentum $(λ)$ of the flow. We identify the region of the parameter space in $λ-{\cal E}$ plane that admits the flow to possess multiple critical points for KTN black hole. We examine the modification of the parameter space due to $a_{\rm k}$ and $n$ and find that the role of $a_{\rm k}$ and $n$ in determining the parameter space is opposite to each other. This clearly indicates that the NUT parameter $n$ effectively mitigates the effect of black hole rotation in deciding the accretion flow structure. Further, we calculate the maximum disc luminosity ($L_{\rm max}$) corresponding to the accretion solutions around the KTN black hole and for a given set of $a_{\rm k}$ and $n$. In addition, we also investigate all possible flow topologies around the naked singularity and find that there exists a region around the naked singularity which remains inaccessible to the flow. We study the critical point properties for naked singularities and find that the flow possesses maximum of four critical points. Finally, we obtain the parameter space for multiple critical points for naked singularity and find that parameter space is shrunk and shifted to lower $λ$ and higher ${\cal E}$ side as $a_{\rm k}$ is increased which ultimately disappears.

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arXiv2020

Properties of two-temperature magnetized advective accretion flow around rotating black hole

We study the two-temperature magnetized advective accretion flow around the Kerr black holes. During accretion, ions are heated up due to viscous dissipation, and when Coulomb coupling becomes effective, they transfer a part of their energy to the electrons. On the contrary, electrons lose energy due to various radiative cooling processes, namely bremsstrahlung, synchrotron, and Comtonization processes, respectively. To account for the magnetic contribution inside the disc, we consider the toroidal magnetic fields which are assumed to be dominant over other components. Moreover, we adopt the relativistic equation of state to describe the thermal characteristics of the flow. With this, we calculate the global transonic accretion solutions around the rotating black holes. We find that accretion solution containing multiple critical points may harbor shock wave provided the standing shock conditions are satisfied. Further, we investigate the shock properties, such as shock location ($x_s$) and compression ratio ($R$) that delineate the post-shock corona (hereafter PSC) and find that the dynamics of PSC is controlled by the flow parameters, such as accretion rate (${\dot m}$) and magnetic fields ($β$, defined as the ratio of gas pressure to the magnetic pressure), etc. Finally, we calculate the emission spectra of the accretion flows containing PSC and indicate that both ${\dot m}$ and $β$ play the pivotal roles in explaining the spectral state transitions commonly observed for black hole X-ray binaries.

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arXiv2019

Shocks in relativistic viscous accretion flows around Kerr black holes

We study the relativistic viscous accretion flows around the Kerr black holes. We present the governing equations that describe the steady state flow motion in full general relativity and solve them in 1.5D to obtain the complete set of global transonic solutions in terms of the flow parameters, namely specific energy (${\cal E}$), specific angular momentum (${\cal L}$) and viscosity ($α$). We obtain a new type of accretion solution which was not reported earlier. Further, we show for the first time to the best of our knowledge that viscous accretion solutions may contain shock waves particularly when flow simultaneously passes through both inner critical point ($r_{\rm in}$) and outer critical point ($r_{\rm out}$) before entering into the Kerr black holes. We examine the shock properties, namely shock location ($r_s$) and compression ratio ($R$, the measure of density compression across the shock front) and show that shock can form for a large region of parameter space in ${\cal L}-{\cal E}$ plane. We study the effect of viscous dissipation on the shock parameter space and find that parameter space shrinks as $α$ is increased. We also calculate the critical viscosity parameter ($α^{\rm cri}$) beyond which standing shock solutions disappear and examine the correlation between the black hole spin ($a_k$) and $α^{\rm cri}$. Finally, the relevance of our work is conferred where, using $r_s$ and $R$, we empirically estimate the oscillation frequency of the shock front ($ν_{QPO}$) when it exhibits Quasi-periodic (QP) variations. The obtained results indicate that the present formalism seems to be potentially viable to account for the QPO frequency in the range starting from milli-Hz to kilo-Hz as $0.386~{\rm Hz}\le ν_{QPO} \left(\frac{10M_\odot}{M_{BH}} \right) \le 1312$ Hz for $a_k=0.99$, where $M_{BH}$ stands for the black hole mass.

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arXiv2019

A Possible Model for the Long-Term Flares of Sgr A*

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*.

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arXiv2019

Accretion-ejection in rotating black holes: a model for `outliers' track of radio-X-ray correlation in X-ray binaries

We study the global accretion-ejection solutions around a rotating black hole considering three widely accepted pseudo-Kerr potentials that satisfactorily mimic the space-time geometry of rotating black holes. We find that all the pseudo potentials provide standing shock solutions for large range of flow parameters. We identify the effective region of the shock parameter space spanned by energy ($\mathcal{E}_{\text{in}}$) and angular momentum ($λ_{\text{in}}$) measured at the inner critical point ($x_{\text{in}}$) and find that the possibility of shock formation becomes feeble when the viscosity parameter ($α$) is increased. In addition, we find that shock parameter space also depends on the adiabatic index ($γ$) of the flow and the shock formation continues to take place for a wide range of $γ$ as $1.5 \le γ\le 4/3$. For all the pseudo potentials, we calculate the critical viscosity parameter ($α_{\text{shock}}^{\text{cri}}$) beyond which standing shock ceases to exist and compare them as function of black hole spin ($a_k$). We observe that all the pseudo potentials under consideration are qualitatively similar as far as the standing shocks are concerned, however, they differ both qualitatively and quantitatively from each other for rapidly rotating black holes. Further, we compute the mass loss from the disc using all three pseudo potentials and find that the maximum mass outflow rate ($R^{\rm max}_{\dot m}$) weakly depends on the black hole spin. To validate our model, we calculate the maximum jet kinetic power using the accretion-ejection formalism and compare it with the radio jet power of low-hard state of the black hole X-ray binaries (hereafter XRBs). The outcome of our results indicate that XRBs along the `outliers' track might be rapidly rotating.

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arXiv2019

Low angular momentum relativistic hot accretion flow around Kerr black holes with variable adiabatic index

We study the relativistic, time-independent, low angular momentum, inviscid, advective accretion flow around Kerr black hole. Considering the relativistic equation of state (REoS), we examine the transonic properties of the flow and find that there exists an upper bound of the location of the physically accepted critical point ($r^{\rm max}_{\rm out}$). However, no such limit exists when an ideal gas equation of state (IEoS) is assumed to describe the flow. Further, we calculate the global accretion solutions that contain shock waves and separate the domain of parameter space in angular momentum ($λ$) and energy (${\cal E}$) plane. We find ample disagreement between the shock parameter spaces obtained for REoS and IEoS, respectively. In general, post-shock flow (equivalently post-shock corona, hereafter PSC) is characterized by shock location ($r_s$) and compression ratio ($R$, measure of density compression across the shock front) which are uniquely determined for flow with given input parameters, namely $({\cal E}, λ)$. Using $r_s$ and $R$, we empirically compute the oscillation frequency ($ν_{QPO}$) of the shock front which is in general quasi-periodic (QP) in nature and retrace the domain of shock parameter space in the $r_s-R$ plane in terms of $ν_{QPO}$ for REoS around the weakly as well as rapidly rotating black holes. Finally, we indicate the relevance of the present work to explain the plausible origin of high frequency QPO (HFQPO) and its connection with the spin ($a_k$) of the Galactic black hole sources.

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arXiv2018

Limitations of Pseudo-Newtonian approach in studying the accretion flow around Kerr black hole

We study the relativistic accretion flow around a generic stationary axisymmetric space-time and obtain an effective potential ($Φ^{\rm eff}$) that accurately mimics the general relativistic features of Kerr black hole having spin $0\le a_k <1$. Considering the accretion disc confined around the equatorial plane of a rotating black hole and using the relativistic equation of state, we examine the properties of the relativistic accretion flow and compare it with the same obtained form semi-relativistic as well as non-relativistic accretion flows. Towards this, we first investigate the transonic properties of the accretion flow around the rotating black hole where good agreement is observed for relativistic and semi-relativistic flows. Further, we study the non-linearities such as shock waves in accretion flow. Here also we find that the shock properties are in agreement for both relativistic and semi-relativistic flows irrespective of the black hole spin ($a_k$), although it deviates significantly for non-relativistic flow. In fact, when the particular shocked solutions are compared for flows with identical outer boundary conditions, the positions of shock transition in relativistic and semi-relativistic flows agree well with deviation of $6-12\%$ for $0 \le a_k \le 0.99$, but vast disagreement is observed for non-relativistic flow. In addition, we compare the parameter space for shock to establish the fact that relativistic as well as semi-relativistic accretion flow dynamics do show close agreement irrespective of $a_k$ values, whereas non-relativistic flow fails to do so. With these findings, we point out that semi-relativistic flow including $Φ^{\rm eff}$ satisfactorily mimics the relativistic accretion flows around Kerr black hole. Finally, we discuss the possible implications of this work in the context of dissipative advective accretion flow around Kerr black holes.

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arXiv2018

Standing shocks in magnetized advection accretion flows onto a rotating black hole

We present the global structure of magnetized advective accretion flow around the rotating black holes in presence of dissipation. By considering accretion flow to be threaded by toroidal magnetic fields and by assuming synchrotron radiative mechanism to be the dominant cooling process, we obtain global transonic accretion solutions in terms of dissipation parameters, such as viscosity ($α_B$), accretion rate (${\dot m}$) and plasma-$β$, respectively. In the rotating magnetized accretion flow, centrifugal barrier is developed in the nearby region of the black hole that triggers the discontinuous shock transition in the flow variables. Evidently, the shock properties and the dynamics of the post-shock flow (hereafter post-shock corona (PSC)) are being governed by the flow parameters. We study the role of dissipation parameters in the formation of standing shock wave and find that global shocked accretion solutions exist both in gas pressure dominated flows and in magnetic pressure dominated flows. In addition, we observe that standing shock continues to form around the rapidly rotating black holes as well. We identify the range of dissipation parameters that permits shocked accretion solutions and find that standing shocks continue to form even in presence of high dissipation limit, although the likelihood of shock formation diminishes with the increase of dissipation. Further, we compute the critical accretion rate (${\dot m}^{\rm cri}$) that admits shock and observe that standing shock exists in a magnetically dominated accretion flow when the accretion rate lies in general in the sub-Eddington domain. At the end, we calculate the maximum dissipated energy that may be escaped from the PSC and indicate its possible implication in the astrophysical context.

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arXiv2018

Advective accretion flow properties around rotating black holes - application to GRO J1655-40

We examine the properties of the viscous dissipative accretion flow around rotating black holes in presence of mass loss. Considering thin disc approximation, we self-consistently calculate the inflow-outflow solutions and observe that the mass outflow rates decreases with the increase of viscosity parameter ($α$). Further, we carry out the model calculation of Quasi-periodic Oscillation frequency ($ν_{\rm QPO}$) that is frequently observed in black hole sources and observe that $ν^{\rm max}_{\rm QPO}$ increases with the increase of black hole spin ($a_k$). Then, we employ our model in order to explain the High Frequency Quasi-periodic Oscillations (HFQPOs) observed in black hole source GRO J1655-40. While doing this, we attempt to constrain the range of $a_k$ based on observed HFQPOs ($\sim$ 300 Hz and $\sim$ 450 Hz) for the black hole source GRO J1655-40.

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arXiv2017

Standing Shocks in Magnetized Dissipative Accretion Flow around Black Holes

We explore the global structure of the accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. The accretion flow is optically thin and advection dominated. Synchrotron radiation is considered to be the active cooling mechanism in the flow. With this, we obtain the global transonic accretion solutions and show that centrifugal barrier in the rotating magnetized accretion flow causes a discontinuous transition of the flow variables in the form of shock waves. The shock properties and the dynamics of the post-shock corona are affected by the flow parameters such as viscosity, cooling rate and strength of the magnetic fields. The shock properties are investigated against these flow parameters. We further show that for given set of boundary parameters at the outer edge of the disc, accretion flow around a black hole admits shock when the flow parameters are tuned for a considerable range.

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arXiv2017

Properties of Two-Temperature Dissipative Accretion Flow Around Black Holes

We study the properties of two-temperature accretion flow around a non-rotating black hole in presence of various dissipative processes where pseudo-Newtonian potential is adopted to mimic the effect of general relativity. The flow encounters energy loss by means of radiative processes acted on the electrons and at the same time, flow heats up as a consequence of viscous heating effective on ions. We assumed that the flow is exposed with the stochastic magnetic fields which leads to Synchrotron emission of electrons and these emissions are further strengthen by Compton scattering. We obtain the two-temperature global accretion solutions in terms of dissipation parameters, namely, viscosity ($α$) and accretion rate (${\dot m}$), and find for the first time in the literature that such solutions may contain standing shock waves. Solutions of this kind are multi-transonic in nature as they simultaneously pass through both inner critical point ($x_{\rm in}$) and outer critical point ($x_{\rm out}$) before crossing the black hole horizon. We calculate the properties of shock induced global accretion solutions in terms of the flow parameters. We further show that two-temperature shocked accretion flow is not a discrete solution, instead such solution exists for wide range of flow parameters. We identify the effective domain of the parameter space for standing shock and observe that parameter space shrinks as the dissipation is increased. Since the post-shock region is hotter due to the effect of shock compression, it naturally emits hard X-rays and therefore, the two-temperature shocked accretion solution has the potential to explain the spectral properties of the black hole sources.

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arXiv2017

Properties of magnetically supported dissipative accretion flow around black holes with cooling effects

We investigate the global structure of the advection dominated accretion flow around a Schwarzschild black hole where the accretion disc is threaded by toroidal magnetic fields. We consider synchrotron radiative process as an effective cooling mechanism active in the flow. With this, we obtain the global transonic accretion solutions by exploring the variety of boundary conditions and dissipation parameters, namely accretion rate (${\dot m}$) and viscosity ($α_B$). The fact that depending on the initial parameters, steady state accretion flows can possess centrifugally supported shock waves. These global shock solutions exist even when the level of dissipation is relatively high. We study the properties of shock waves and observe that the dynamics of the post-shock corona (hereafter, PSC) is regulated by the flow parameters. Interestingly, we find that shock solution disappears completely when the dissipation parameters exceed their critical values. We calculate the critical values of viscosity parameter ($α^{\rm cri}_B$) adopting the canonical values of adiabatic indices as $γ=4/3$ (ultra-relativistic) and $1.5$ (semi-non-relativistic) and find that in the gas pressure dominated domain, $α^{\rm cri}_B \sim 0.4$ for $γ=4/3$ and $α^{\rm cri}_B \sim 0.27$ for $γ=1.5$, respectively. We further show that global shock solutions are relatively more luminous compared to the shock free solutions. Also, we have calculated the synchrotron spectra for shocked solutions. When the shock is considered to be dissipative in nature, it would have an important implication as the available energy at PSC can be utilized to power the outflowing matter escaped from PSC. Towards this, we calculate the maximum shock luminosity and discuss the observational implication of our present formalism.

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arXiv2017

Estimation of mass outflow rates from dissipative accretion disc around rotating black holes

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 self-consistently. 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 ($λ_{\rm in}$) and the energy (${\cal E}_{\rm in}$) at the inner sonic point ($x_{\rm in}$), 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 $R_{\dot m}$ (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 ($R_{\dot{m}}^{\rm max}$) in terms of viscosity parameter ($α$) as well as black hole spin ($a_k$) and obtain the limiting range as $3\% \le R_{\dot{m}}^{\rm max} \le 19\%$. Moreover, we calculate the viable range of $α$ that admits the coupled inflow-outflow solutions and find that $α\lesssim 0.25$ for $R_{\dot m} \ne 0$. 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 ($\sim 450$ Hz), we constrain the spin value of the source as $a_k \ge 0.57$.

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