Palit, S., Chakrabarti, Sandip K., Debnath, D., Rao, A. R., Nandi, A., Yadav, Vipin K., ...
We present the results of simulations of shadows cast by a zone plate telescope which may have one to four pairs of zone plates. From the shadows we reconstruct the images under various...
Fresnel zone plate telescopes for X-ray imaging I: experiments with a quasi-parallel beam (2009)
Chakrabarti, Sandip K., Palit, S., Debnath, D., Nandi, A., Yadav, V., Sarkar, Ritabrata
Combination of Fresnel Zone Plates (FZP) can make an excellent telescope for imaging in X-rays. We present here the results of our experiments with several pairs of tungsten made Fresnel Zone plates...
Studies of dissipative standing shock waves around black holes (2009)
Das, Santabrata, Chakrabarti, Sandip K., Mondal, Soumen
We investigate the dynamical structure of advective accretion flow around stationary as well as rotating black holes. For a suitable choice of input parameters, such as, accretion rate ($\dot {\cal...
Chakrabarti, Sandip K., Dutta, Broja G., Pal, P. S.
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot regions embedded in Keplerian discs. Observational evidence of...
Ghosh, Himadri, Chakrabarti, Sandip K., Laurent, Philippe
We compute the effects of thermal Comptonization of soft photons emitted from a Kep- lerian disk around a black hole by the post-shock region of a sub-Keplerian flow, known as the CENtrifugal...
Chakrabarti, Sandip K., Debnath, D., Pal, P. S., Nandi, A., Sarkar, R., Samanta, M. M., ...
Quasi-Periodic Oscillations (QPOs) are very puzzling since they remain totally unexplained by popular earlier models of accretion disks. The significant rms value in power density spectrum implies...
Spectral and timing evolution of GRO J1655-40 during its outburst of 2005 (2009)
Debnath, D., Chakrabarti, Sandip K., Nandi, A., Mandal, S.
In a recent outburst which lasted for 260 days, the black hole candidate GRO J1655-40 exhibited a behaviour similar to its last outburst observed almost eight years ago. We analyze a total of 150...
Spectrum of two component flows around a super-massive black hole: an application to M87 (2008)
Mandal, Samir, Chakrabarti, Sandip K.
We calculate the spectra of two-component accretion flows around black holes of various masses, from quasars to nano-quasars. Specifically, we fit the observational data of M87 very satisfactorily...
Chakrabarti, Sandip K., Debnath, Dipak, Nandi, Anuj, Pal, P. S.
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot blobs embedded in Keplerian disks. Any movement of these...
Dissipative accretion flows around a rotating black hole (2008)
Das, Santabrata, Chakrabarti, Sandip K.
We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only...
Properties of accretion shock waves in viscous flows with cooling effects (2007)
Das, Santabrata, Chakrabarti, Sandip K.
We study the properties of the shock waves for a viscous accretion flow having low angular momentum in presence of synchrotron cooling. We present all possible accretion solutions in terms of flow...
Parameter space study of magnetohydrodynamic flows around magnetized compact objects (2007)
Das, Santabrata, Chakrabarti, Sandip K.
We solve the magnetohydrodynamic (MHD) equations governing axisymmetric flows around neutron stars and black holes and found all possible solution topologies for adiabatic accretion. We divide the...
Propagating Oscillatory Shock Model for QPOS in GRO J1655-40 During the March 2005 Outburst (2005)
Chakrabarti, Sandip K., Nandi, A., Debnath, D., Sarkar, R., Datta, B. G.
GRO 1655-40, a well known black hole candidate, showed renewed X-ray activity in March 2005 after being dormant for almost eight years. It showed very prominent quasi-periodic oscillations. We...
Evidence of Class Transitions in GRS 1915+105 from IXAE Data (2005)
Chakrabarti, Sandip K., Nandi, A., Choudhury, Asit, Chatterjee, Utpal
GRS 1915+105 shows at least twelve distinct classes of light curves. By analysing the data obtained from Indian X-ray Astronomy Experiment (IXAE) instrument aboard IRS-P3 satellite, we show that in...
Class Transitions and Two Component Accretion Flow in GRS 1915+105 (2005)
Chakrabarti, Sandip K., Nandi, Anuj, Chatterjee, A. K., Choudhury, A. K., Chatterjee, U.
The light curve of the galactic micro-quasar GRS 1915+105 changes in at least thirteen different ways which are called classes. We present examples of the transitions from one class to another as...
Signatures of Accretion Shocks in Broadband Spectrum of Advective Flows Around Black Holes (2005)
Mandal, Samir, Chakrabarti, Sandip K.
We compute the effects of the centrifugal pressure supported shock waves on the emitted spectrum from an accretion disk primarily consisting of low angular momentum matter. Electrons are very...
Spectral Properties of Black Holes in Gamma Rays (2005)
Black holes are the most compact objects in the universe. Therefore, matter accreting onto is likely to radiate photons of energy comparable to very high gravitational potential energy. We discuss...
Identification of Shocks in the Spectra from Black Holes (2005)
Mandal, Samir, Chakrabarti, Sandip K.
We study the spectral properties of a low angular momentum flow as a function of the shock strength, compression ratio, accretion rate and flow geometry. In the absence of a satisfactory description...
Molecular Hydrogen Formation During Dense Interstellar Cloud Collapse (2005)
Acharyya, K., Chakrabarti, Sandip K., Chakrabarti, S.
We study the evolution of molecular hydrogen on the grain surfaces and in the gas phase using both the rate equation (which tracks the average number of molecules) and the master equation (which...
Mandal, Samir, Chakrabarti, Sandip K.
Centrifugal barrier supported boundary layer (CENBOL) of a black hole affects the spectrum exactly in the same way the boundary layer of a neutron star does. The CENBOL is produced due to standing or...
SS 433: Results of a Recent Multi-wavelength Campaign (2005)
Chakrabarti, Sandip K., Anandarao, B. G., Pal, S., Mondal, Soumen, Nandi, A., Bhattacharyya, A., ...
We conducted a multi-wavelength campaign in September-October, 2002, to observe SS 433. We used 45 meter sized 30 dishes of Giant Meter Radio Telescope (GMRT) for radio observation, 1.2 meter...
Analytical studies of particle dynamics in bending waves in planetary rings (2005)
Bhattacharyya, A., Chakrabarti, Sandip K.
Particles inside a planetary ring are subject to forcing due to the central planet, moons in inclined orbits, self-gravity of the ring and other forces due to radiation drag, collisional effects and...
Mass accretion rate of the galactic black hole A0620-00 in its quiescent state (2005)
Pal, Sabyasachi, Chakrabarti, Sandip K.
Our recent radio observation using the Giant Meter Radio Telescope (GMRT) of the galactic black hole transient A0620-00 at 1.280GHz revealed a micro-flare of a few milli-Jansky. Assuming an...
VLF observation during Leonid Meteor Shower-2002 from Kolkata (2005)
Chakrabarti, Sandip K., Pal, S., Acharyya, K., Mandal, S., Chakrabarti, S., Khan, R., ...
Using a Gyrator-II Loop antenna tuned at 19.0Khz, we monitored the meteor shower during 17-24th November, 2002. We observe the primary peak at 3h58m (UT) on the 19th of November, 2002. We distinctly...
Monitoring of Sudden Ionospheric Disturbances (SID) from Kolkata (INDIA) (2005)
Chakrabarti, Sandip K., Acharyya, K., Bose, B., Mandal, S., Chatterjee, A., Nandi, N. M., ...
We report our first results of monitoring sudden ionospheric disturbances (SID). We present data taken continuously for two weeks during 20th Sept. 2002 and 4th Oct. 2002. We compare the effects of...
Role of Disk models in Indentifying Astrophysical Black Holes (2005)
We discuss how disk models may limit the scope of identifying astrophysical black holes. We show that the standard Keplerian thin disk model, the thick disk model, slim disks, ADAFs etc. are...
Spectral Properties of a Two Component and Two Temperature Advective Flow (2005)
Mandal, Samir, Chakrabarti, Sandip K.
Low angular momentum accretion flows very often have centrifugal pressure supported standing shock waves which can accelerate flow particles. The accelerated particles in turn emit synchrotron...
QPOs from Radial and Vertical Oscillation of Shocks in Advective Accretion Flows (2005)
Chakrabarti, Sandip K., Acharyya, K., Molteni, D.
We present results of several numerical simulations of two dimensional advective flows which include cooling processes. We show that the computed light curve is similar to the $\chi$ state in GRS...
Spectral Signatures of Winds from Accretion Disks Around Black Holes (2005)
Chakrabarti, Sandip K., Nandi, A., Rao, A. R.
We show that with the wind/jet activity, the spectral index of hard X-ray is changed in galactic microquasars. When mass loss takes place, the spectrum becomes softer and when mass gain takes place,...
Photometric Evidence of Bullets in SS433 Jet (2005)
Chakrabarti, Sandip K., Nandi, A., Pal, S., Anandarao, B. G., Mandal, Soumen
We report the photometric evidence of bullet like features in SS433 in X-rays, Infra-red and Radio bands through a multi-wavelength campaign.
A GHz Flare in a Quiescent Black Hole and A Determination of the Mass Accretion Rate (2005)
Pal, S., Chakrabarti, Sandip K.
If the total energy of a radio flare is known, one can estimate the mass accretion rate of the disk by assuming equipartition of magnetic energy and the gravitational potential energy of accreting...
Results of Recent Multi-wavelength Campaign of SS433 (2005)
Pal, S., Chakrabarti, Sandip K., Goswami, K., Nandi, A., Rao, B. G. Ananda, Mondal, Soumen
We conducted multi wavelength campaign on SS433 in Sept. 2002 using X-ray, B, Infra-Red and radio telescopes. We observed variabilities on a time-scale of few minutes in all the wavelengths. We...
Class Transitions in Black Holes (2005)
A black hole spectrum is known to change from the hard state to the soft state when the energy spectral index $\alpha$ ($F_E \propto E^{-\alpha}$) in, say, 2-20 keV range changes from $\alpha \sim...
Numerical Simulations Reveal the Origin of QPOs in Black Hole Candidates (2005)
We present results of various types of numerical simulations of black hole accretion disks and find that those flows which are relatively non-dissipative and which contain accretion shocks are the...
Radiatively Driven Jets around Black Holes (2004)
Chattopadhyay, Indranil, Chakrabarti, Sandip K.
The hot, puffed up, post-shock region of an advective disc is the source of high energy photons and also the jets and outflows. We study the relativistic equations of motion of jets as these high...
X-ray Observation of SS 433 with RXTE (2004)
Nandi, A., Chakrabarti, Sandip K., Belloni, Tomaso, Goldoni, P.
Apart from regular monitoring by ASM, the compact object SS 433 was observed with RXTE several times last two/three years. We present the first analysis of these observations. We also include the...
Properties of Accretion Shocks in Viscous Flows with Cooling Effects (2004)
Das, Santabrata, Chakrabarti, Sandip K.
Low angular momentum accretion flows can have standing and oscillating shock waves. We study the region of the parameter space in which multiple sonic points occur in viscous flows in presence of...
Properties of Accretion Shock Waves in Viscous Flows Around Black Holes (2004)
Chakrabarti, Sandip K., Das, Santabrata
Accretion flows having low angular momentum and low viscosity can have standing shock waves. These shocks arise due to the presence of multiple sonic points in the flow. We study the region of the...
Computation of outflow rates from accretion disks around black holes (2004)
Das, Santabrata, Chattopadhyay, Indranil, Nandi, A., Chakrabarti, Sandip K.
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...
The effect of cooling on time dependent behaviour of accretion flows around black holes (2004)
Chakrabarti, Sandip K., Acharyya, K., Molteni, D.
We present the results of several numerical simulations of two dimensional axi-symmetric accretion flows around black holes using Smoothed Particle Hydrodynamics (SPH) in the presence of cooling...
Chakrabarti, Sandip K., Pal, S., Nandi, A., Anandarao, B. G., Mondal, Soumen
SS433 is well-known for its precessing twin jets having optical bullets inferred through {\it spectroscopic} observation of $H_\alpha$ lines. Recently, Chakrabarti et al. (2002) described processes...
Study of Accretion Processes on Black Holes: Fifty Years of Developments (2004)
Fifty years ago, in 1952, the first significant paper on accretion flows was written by Bondi. The subject has grown exponentially since then. In fact, today many of the satellites engaged in space...
Radiatively driven electron-positron jets from two component accretion flows (2004)
Chattopadhyay, Indranil, Das, Santabrata, Chakrabarti, Sandip K.
Matter accreting onto black holes has long been known to have standing or oscillating shock waves. The post-shock matter puffs up in the form of a torus, which intercepts soft photons from the outer...
Naik, S., Rao, A. R., Chakrabarti, Sandip K.
We present the results of a detailed analysis of RXTE observations of class $\omega$ which show an unusual state transition between high-soft and low-soft states in the microquasar GRS 1915+105. Out...
Quasi-Periodic Oscillations in Numerical Simulation of Accretion Flows Around Black Holes (2002)
Chakrabarti, Sandip K., Acharyya, K., Molteni, D.
We present results of several numerical simulations of two dimensional axi-symmetric accretion flows around black holes using the Smoothed Particle Hydrodynamics (SPH). We consider both stellar black...
On the Ejection Mechanism of Bullets in SS 433 (2002)
Chakrabarti, Sandip K., Goldoni, P., Wiita, P. J., Nandi, A., Das, S.
We discuss plausible mechanisms to produce bullet-like ejecta from the precessing disk in the SS 433 system. We show that non-steady shocks in the sub-Keplerian accretion flow can provide the basic...
State transition between high-soft and low-soft states observed in GRS 1915+105 (2002)
Naik, S., Rao, A. R., Chakrabarti, Sandip K.
We present the results of a detailed analysis of RXTE observations which show an unusual state transition between high-soft and low-soft states in the microquasar GRS 1915+105. The RXTE pointed...
Radiatively Driven Plasma Jets around Compact Objects (2002)
Chattopadhyay, Indranil, Chakrabarti, Sandip K.
Matter accreting onto black holes may develop shocks due to the centrifugal barrier. A part of inflowing matter in the post-shock flow is deflected along the axis in the form of jets. Post-shock flow...
Accretion onto a Black Hole in the Presence of Bremsstrahlung Cooling - Parameter Space Study (2002)
Manickam, Sivakumar G., Chakrabarti, Sandip K.
The dynamics of accretion onto a schwarzschild black hole is studied using Paczynski-Wiita pseudo newtonian potential. Steady state solution of the flow equations is obtained using thin disc...
Bending Instability of an Accretion Disc Around a Black Hole (2001)
Molteni, D., Acharya, K., Kuznetsov, Oleg, Bisikalo, D., Chakrabarti, Sandip K.
We demonstrate that generically an accretion disk around a compact object could have a new type of instability in that the accretion flow need not be symmetric with respect to the equatorial plane...
Standing Shocks around Black Holes: An Analytical Study (2001)
Das, Santabrata, Chattopadhyay, Indranil, Chakrabarti, Sandip K.
We compute locations of sonic points and standing shock waves in a thin, axisymmetric, adiabatic flow around a Schwarzschild black hole. We use completely analytical method to achieve our goal. Our...
Stability of Accretion Disks in Presence of Nucleosynthesis (2001)
Mukhopadhyay, Banibrata, Chakrabarti, Sandip K.
We study the effect of nuclear reaction on a thin, axisymmetric, differentially rotating, inviscid, steady accretion flow around a black hole from an analytical point of view. We find that for most...
Fundamental States of Accretion/Jet Configuration and the Black Hole Candidate GRS1915+105 (2000)
Chakrabarti, Sandip K., Nandi, Anuj
Advective disk paradigm of black hole accretion includes self-consistent formation of shocks and outflows from post-shock region. We apply this paradigm to understand rich variation of the light...
Nandi, Anuj, Manickam, Sivakumar G., Rao, A. R., Chakrabarti, Sandip K.
A few classes of the light curve of the black hole candidate GRS 1915+105 have been analyzed in detail. We discover that unlike the previous findings, QPOs occasionally occur even in the so-called...
Relation of Light Curve Behaviour with Accretion Rates in Black Hole Candidate GRS1915+105 (2000)
Chakrabarti, Sandip K., Nandi, A., Manickam, S. G.
We report some properties of the light curves of GRS 1915+105 and present their interpretation using the variation of net accretion rate.
Effect of an Accretion Disk on the Gravitational Wave Signal from an Inspiralling Binary (2000)
Since black holes can only accrete sub-Keplerian matter, a companion black hole orbiting on a circular and instantaneously Keplerian orbit around a central, massive black hole in a galactic Centre...
State-or-the-art Accretion and Wind Solutions Around Black Holes (2000)
We report all possible basic solutions of an advective disk model and use them to explain major observations from black hole candidates.
Bulk Motion Comptonization - a sure sign of Black Holes (2000)
Chakrabarti, Sandip K., Chattopadhyay, Indranil
Bulk motion Comptonization utilizes properties of both matter and radiation close to the horizon of a black hole. Computation with these considerations produce hard tails of energy spectral slope...
Generation and Acceleration of Jets from Effective Boundary Layer around Black Hole (2000)
Chattopadhyay, Indranil, Chakrabarti, Sandip K.
We propose the processes of generation and radiative acceleration of jets from the centrifugal pressure dominated boundary layer around a black hole.
On Radiative Acceleration of Jets and Outflows from Advective Disks (2000)
Chattopadhyay, Indranil, Chakrabarti, Sandip K.
Jets and outflows are known to form out of advective accretion flows around black holes. Hard photons from the centrifugal barrier directly hit the electrons and deposit momentum on them. For...
Chakrabarti, Sandip K., Manickam, Sivakumar G., Nandi, Anuj K., Rao, A. R.
Accretion and outflows are common in systems which include black holes. Especially important is the case of the well known micro-quasar GRS1915+105 in our own galaxy, where super-luminal outflows are...
Jets and Outflows From Advective Accretion Disks (2000)
Jets and outflows must be produced directly from accretion disks and inflows, especially when the central gravitating objects are compact, such as neutron stars and black holes, and themselves are...
Jets, Disks and Spectral States of Black Holes (2000)
We show that outflow rates in jets directly depend on the spectral states of black holes. In particular, in soft states, when the Comptonized electrons are cold, outflow rate is close to zero. In...
Classification of Light curves of the Black Hole Candidate GRS1915+105 (2000)
Nandi, Anuj, Manickam, Sivakumar G., Chakrabarti, Sandip K.
The black hole candidate GRS 1915+105 exhibits a rich variety of variability. Assuming that the earlier paradigm of black hole accretion which includes a shock is applicable for this system as well,...
Advective Flow Paradigm And Microquasar GRS1915+105 (2000)
Advective accretion disks and winds are the most self-consistent solutions today. We describe this paradigm briefly and show how it attempts to explain some of the interesting observations of the...
Understanding Galactic Black Hole Candidate GRS 1915+105 (2000)
Chakrabarti, Sandip K., Manickam, S. G., Nandi, A., Rao, A. R.
We interpret observed features of the black hole candidate GRS1915+105 in the light of the advective flow paradigm. The light curve of this black hole is seen to be of four classes, Soft, Hard,...
Scattering of Dirac Waves off Kerr Black Holes (2000)
Chakrabarti, Sandip K., Mukhopadhyay, Banibrata
Chandrasekhar separated the Dirac equation for spinning and massive particles in Kerr geometry into radial and angular parts. Here we solve the complete wave equation and find out how the Dirac wave...
Dirac equation in Kerr geometry and its solution (2000)
Chakrabarti, Sandip K., Mukhopadhyay, Banibrata
Chandrasekhar separated the Dirac equation for spinning and massive particles in Kerr geometry into radial and angular parts. In the present review, we present solutions of the complete wave equation...
Solution of Dirac equation around a spinning Black Hole (2000)
Mukhopadhyay, Banibrata, Chakrabarti, Sandip K.
Chandrasekhar separated the Dirac equation for spinning and massive particles in Kerr geometry in radial and angular parts. Chakrabarti solved the angular equation and found the corresponding...
Adenine Abundance in a Collapsing Molecular Cloud (2000)
Chakrabarti, Sandip K., Chakrabarti, Sonali
A vital ingredient of DNA molecule named adenine may be produced by successive addition of HCN during molecular cloud collapse and star formation. We compute its abundance in a collapsing cloud as a...
Can DNA bases be produced during molecular cloud collapse? (2000)
Chakrabarti, Sonali, Chakrabarti, Sandip K.
Using a reasonably large chemical reaction network consisting of 421 species, we show that along with normal chemical evolution of molecular cloud during collapse and star formation, significant...
Nucleosynthesis in accretion flows around Black Holes (1999)
Mukhopadhyay, Banibrata, Chakrabarti, Sandip K.
Significant nucleosynthesis is possible in the centrifugal pressure-supported dense and hot region of the accretion flows which deviate from Keplerian disks around black holes. We compute composition...
Mass Outflow Rate From Accretion Discs around Compact Objects (1999)
Das, Tapas K., Chakrabarti, Sandip K.
We compute mass outflow rates from accretion disks around compact objects, such as neutron stars and black holes. These computations are done using combinations of exact transonic inflow and outflow...
Chakrabarti, Sandip K., Manickam, Sivakumar G.
We discover a definite correlation between the frequency of the quasi-periodic oscillations (QPO) in quiescence states and the duration of the quiescence state of the transient X-ray source GRS...
Outflows are common in many astrophysical systems which contain black holes and neutron stars. Difference between stellar outflows and outflows from these systems is that the outflows in these...
Semi-analytical Solution of Dirac equation in Schwarzschild Geometry (1999)
Mukhopadhyay, Banibrata, Chakrabarti, Sandip K.
Separation of the Dirac equation in the spacetime around a Kerr black hole into radial and angular coordinates was done by Chandrasekhar in 1976. In the present paper, we solve the radial equations...
Neutron Disks Around Black Holes (1999)
Chakrabarti, Sandip K., Mukhopadhyay, Banibrata
We study nucleosynthesis in low accretion rate hot advective flows around black holes. We find that matter is generally photo-dissociated into protons and neutrons inside the disk. These neutrons...
Global Inflow and Outflow Solutions (GIOS) around a Black Hole (1998)
Twenty five years have passed by since models of accretions and jets have separately emerged. Today, it is understood that these two objects are related to each other in a fundamental way. In a...
Spectral Softening due to Winds in Accretion Disks (1998)
Accretion flows may produce profuse winds when they have positive specific energy. Winds deplete matter from the inner region of the disk and makes the inner region thinner, optically. Since there...
Mass Outflow Rate From Advective Accretion Disks around Compact Objects (1998)
Das, Tapas K., Chakrabarti, Sandip K.
We compute mass outflow rates from advective accretion disks around compact objects, such as neutron stars and black holes. These computations, for the first time, are done using combinations of...
Accretion Disks Around Black Holes: Twenty Five Years Later (1998)
We study the progress of the theory of accretion disks around black holes in last twenty five years and explain why advective disks are the best bet in explaining varied stationary and non-stationary...
Identification of Astrophysical Black Holes (1998)
Black holes are by definition black, and therefore cannot be directly observed by using electromagnetic radiations. Convincing identification of black holes must necessarily depend on the...
Estimation of the Mass Outflow Rate From Compact Objects (1998)
Outflows are common in many astrophysical systems which contain black holes and neutron stars. Difference between stellar outflows and outflows from these systems is that the outflows in these...
Bondi Flows on Compact Objects Revisited (1997)
Chakrabarti, Sandip K., Sahu, Soumitri A.
We revisit Bondi flows on black holes, naked singularities and neutron stars keeping in mind recent progress in understanding of the flow behaviour near compact objects. In an adiabatic spherical...
Close to a black hole, the density of the sub-Keplerian accreting matter becomes higher compared to a spherical flow due to the presence of a centrifugal barrier independent of whether or not a...
Recent Progresses Of Accretion Disk Models Around Black Holes (1997)
Accretion disk models have evolved from Bondi flows in the 1950s to Keplerian disks in the 1970s and finally to advective transonic flows in the 1990s. We discuss recent progresses in this subject...
Accretion Processes Around Black Holes And Neutron Stars: Advective Disk Paradigm (1997)
We review models which include advective accretion disks onto compact objects and discuss the influence of the centrifugal pressure supported high density region close to the compact objects on the...
Numerical Simulations of Rotating Accretion Flows near a Black Hole (1997)
Ryu, Dongsu, Chakrabarti, Sandip K.
We present time-dependent solutions of thin, supersonic accretion flows near a black hole and compare them with analytical solutions. Such flows of inviscid, adiabatic gas are characterized by the...
Numerical Simulations Of Advective Flows Around Black Holes (1996)
Chakrabarti, Sandip K., Ryu, D., Molteni, D., Sponholz, H., Lanzafame, G., Eggum, G.
We present fully time-dependent solutions of accretion processes on black holes and compare them with analytical solutions. We use Smoothed Particle Hydrodynamics and Total Variation Diminishing...
We review the current understanding of accretion flows around compact objects with a special emphasis on advective disks. We discuss the influence of the centrifugal pressure supported high density...
Aspects of Accretion Processes On a Rotating Black Hole (1996)
We describe the most general nature of accretion and wind flows around a compact object and emphasize on the properties which are special to black hole accretion. The angular momentum distribution in...
Spectral Properties of Galactic and Extragalactic Black Hole Candidates (1996)
We review current theoretical understanding of the spectral properties (low and high states, transition of states, quasi-periodic oscillations etc.) of the low mass as well as supermassive black hole...
New Twists In The Study Of Gravity Wave Emission In Systems With Massive Black Holes (1996)
Traditionlly, gravitational wave emission from a coalescing binary system is computed using point mass approximations without considering any accretion disk. However, it is believed that in many of...
Global Solutions of Viscous Transonic Flows in Kerr Geometry I: Weak Viscosity Limit (1996)
We present fully general relativistic equations governing viscous transonic flows in vertical equilibrium in Kerr geometry. We find the complete set of global solutions (both for Optically thick and...
Zero Energy Rotating Accretion Flows near a Black Hole (1996)
Ryu, Dongsu, Chakrabarti, Sandip K., Molteni, Diego
We characterize the nature of thin, axisymmetric, inviscid, accretion flows of cold adiabatic gas with zero specific energy in the vicinity of a black hole by the specific angular momentum. Using...
Grand Unification of Solutions of Accretion and Winds around Black Holes and Neutron Stars (1996)
We provide the complete set of global solutions of viscous transonic flows (VTFs) around black holes and neutron stars. These solutions describe the optically thick and optically thin flows from the...
Molteni, Diego, Ryu, Dongsu, Chakrabarti, Sandip K.
We compare the results of numerical simulations of thin and quasi-spherical (thick) accretion flows with existing analytical solutions. We use a Lagrangian code based on the Smooth Particle...
Accretion Processes On a Black Hole (1996)
We describe astrophysical processes around a black hole keeping primarily the physics of accretion in mind. In Section 1, we briefly discuss the formation, evolution and detection of black holes. We...
Gravitational Wave Emission From a Binary Black Hole System in Presence of an Accretion Disk (1996)
We study time evolution and gravitational wave emission properties of a black hole orbiting {\it inside} an accretion disk surrounding a massive black hole. We simultaneously solve the structure...
On the Spectral Slopes of Hard X-ray Emission from Black Hole Candidates (1995)
Ebisawa, Ken, Titarchuk, Lev G., Chakrabarti, Sandip K.
Most black hole candidates exhibit characteristic power-law like hard X-ray emission above $\sim$ 10 keV. In the {\em high state}, in which 2 -- 10 keV luminosity is relatively high, the energy index...
Spectral Properties of Accretion Disks Around Galactic and Extragalactic Black Holes (1995)
Chakrabarti, Sandip K., Titarchuk, Lev G.
We study the spectral properties of a very general class of accretion disks which can be decomposed into three distinct components apart from a shock at $r=r_s$: (1) An optically thick Keplerian disk...
We provide complete and global solutions of transonic flows around black holes, in presence of advection, rotation, heating and cooling. We show that for any degree of advection, there may exist two...
Resonance Oscillation Of Radiative Shock Waves In Accretion Disks Around Compact Objects (1995)
Molteni, Diego M., Sponholz, H., Chakrabarti, Sandip K.
We extend our previous numerical simulation of accretion disks with shock waves when cooling effects are also included. We consider bremsstrahlung and other power law processes: $\Lambda \propto...
Grand Unified Model of Accretion Disks Around Black Holes: the Sub-Keplerian Paradigm (1995)
We show that viscous, transonic accretion disks which start with sub-Keplerian angular momentum at the outer boundary reproduce the features of the so-called thick, thin, slim and other accretion...
Velocity Profile of the Ionized Disk and the Mass of the Black Hole in M87 (1994)
We present a theoretical model for the ionized disk in M87 which includes spiral shock waves. The line emission profiles computed from this model at various positions on the disk are found to be in...
Viscosity Prescriptions in Accretion Disks with Shock Waves (1994)
Chakrabarti, Sandip K., Molteni, Diego
We study the evolution of viscous, isothermal, rotating, thin, axisymmetric accretion disks around a compact object using Smoothed Particle Hydrodynamics. We emphasize the effects of different...
D'Silva, Sydney, Chakrabarti, Sandip K.
In paper I, we have studied the conditions under which flux tubes are expelled from adiabatic thick accretion disks. In the present paper, we explore a few other models of thick disks, where flux...
Chakrabarti, Sandip K., D'Silva, Sydney
We study the dynamics of toroidal magnetic flux tubes, symmetric about the rotation axis, inside non-magnetic thick accretion disks around black holes. We present model equations which include...
Chakrabarti, Sandip K., Molteni, Diego
We present results of numerical simulation of thin accretion disks and winds. We use the Smoothed Particle Hydrodynamics (SPH) technique for this purpose. We show that the simulation agrees very well...
Binary Black Holes in Stationary Orbits (1992)
We show that under certain astrophysical conditions a binary system consisting of two compact objects can be stabilized against indefinite shrinking of orbits due to the emission of gravitational...
Naked Singularities as Possible Candidates for Gamma-ray Bursters (1992)
Chakrabarti, Sandip K., Joshi, Pankaj S.
Naked singularities appear naturally in dynamically evolving solutions of Einstein equations involving gravitational collapse of radiation, dust and perfect fluids, provided the rate of accretion is...