• Santabrata Das

      Articles written in Journal of Astrophysics and Astronomy

    • Standing shocks around black holes and estimation of outflow rates

      Santabrata Das Sandip K. Chakrabarti

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      We self-consistently obtain shock locations in an accretion flow by using an analytical method. One can obtain the spectral properties, quasi-periodic oscillation frequencies and the outflow rates when the inflow parameters are known. Since temperature of the CENBOL decides the spectral states of the black hole, and also the outflow rate, the outflow rate is directly related to the spectral states.

    • Editorial

      Samir Mandal Indranil Chattopadhyay Anuj Nandi Santabrata Das

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    • Standing shocks in magnetized dissipative accretion flow around black holes


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      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. The 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 a 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.

    • A comparative study of single-temperature and two-temperature accretion flows around black holes


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      We study the properties of sub-Keplerian accretion disk around a stationary black hole, considering bremsstrahlung, synchrotron and Comptonization of synchrotron photons as radiative cooling mechanisms active in the disk. We obtain the solutions of two-temperature global accretion flow (TTAF) and compare it with the results obtained from single-temperature (STAF) model.We observe that flow properties, in particular, the radial profile of electron and ion temperatures differ noticeably in the adopted models for flows with identical boundary conditions fixed at the outer edge of the disk. Since the electron temperature is one of the key factors to regulate the radiative processes, we argue that physically motivated description of electron temperature needsto be considered in studying the astrophysical phenomena around black holes.

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


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      We examine the properties of the viscous dissipative accretion flow around rotating black holes in the presence of mass loss. Considering the thin disc approximation, we self-consistently calculate the inflow-outflow solutions and observe that the mass outflow rates decrease with the increase in viscosity parameter ($\alpha$). Further, we carry out the model calculation of quasi-periodic oscillation frequency ($\nu_{\rm QPO}$) that is frequentlyobserved in black hole sources and observe that $\nu^{\max}_{\rm QPO}$ increases with the increase of black hole spin ($a_{\rm k}$). Then, we employ our model in order to explain the High Frequency Quasi-Periodic Oscillations (HFQPOs) observedin black hole source GROJ1655-40. 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.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

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