arXiv subjects

Dipak Debnath

Publications and source records attributed to Dipak Debnath.

At least 55 records · Page 3Linked to original sources

arXiv2016

Spectral study of GX 339-4 with TCAF using Swift/XRT and NuSTAR Observation

We fit spectra of galactic transient source GX~339-4 during its 2013 outburst using Two Component Advective Flow (TCAF) solution. For the first time, we are fitting combined NuSTAR and Swift observation with TCAF. We use TCAF to fit 0.8-9.0~keV Swift and 4-79 keV NuSTAR spectra along with the LAOR model. To fit the data we use disk accretion rate, halo accretion rate, size of the Compton cloud and the density jump of advective flows at this cloud boundary as model parameters. From TCAF fitted flow parameters, and energy spectral index we conclude that the source was in the hard state throughout this particular outburst. The present analysis also gives some idea about the broadening of Fe $K_α$ with the accretion rate. Since TCAF does not include Fe line yet, we make use of the `LAOR model' as a phenomenological model and find an estimate of the Kerr parameter to be $\sim 0.99$ for this candidate.

astro-ph.HE↗

arXiv2016

Accretion Flow Properties of MAXI J1543-564 During 2011 Outburst from TCAF Solution

We derive accretion flow properties of the transient black hole candidate (BHC) MAXI~J1543-564 using the RXTE data. We use Two-Component Advective Flow (TCAF) solution to fit the data of the very initial rising phase of outburst (from 2011 May 10 to 2011 May 15). $2.5-25$~keV spectra are fitted using the TCAF solution {\it fits} file as a local additive table model in XSPEC. We extract physical flow parameters such as the two component (Keplerian disk and sub-Keplerian halo) accretion rates and size and the property of the Compton cloud (post shock region close to a black hole). Similar to other classical transient BHCs, monotonic evolution of low frequency quasi-periodic oscillations (QPOs) are observed during the rising phase of the outburst, which is fitted with the propagating oscillatory shock (POS) model which describes how the Compton cloud properties change from day to day. From the nature of variations of TCAF model fitted physical flow parameters and QPOs, we only found hard-intermediate and soft-intermediate spectral states during this phase of the outburst under study. We also calculate frequency of the dominating QPOs from the TCAF model fitted shock parameters, and found that they roughly match with the observed and POS model fitted values. From our spectro-temporal study of the source with TCAF and POS models, the most probable mass of the BHC is found to be $12.6-14.0$~$M_\odot$, or $13^{+1.0}_{-0.4}~M_\odot$.

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arXiv2016

Estimation of Mass of the Black Hole Candidate MAXI J1659-152 using TCAF and POS Models

The Galactic transient black hole candidate (BHC) MAXI~J1659-152 exhibited temporal and spectral evolution during its very first X-ray outburst (2010) after its discovery on 25th Sept. 2010. Our recent studies of a few transient BHCs including MAXI~J1659-152 using Chakrabarti-Titarchuk two-component advective flow (TCAF) solution as an additive table local model in XSPEC revealed details of accretion flow dynamics around the black hole (BH). The TCAF model fitted normalization (N) comes out to be almost constant throughout the entire outburst consisting of several spectral states. We introduce two independent methods to determine the mass ($M_{BH}$) of the BHC, namely, {\it $i)$ keeping TCAF fitted normalization parameter in a narrow range}, and {\it $ii)$ studying evolution of the Quasi-Periodic Oscillation frequency ($ν_{QPO}$) with time, fitted with the propagating oscillatory shock (POS) model}. The predicted mass ranges of the source with these two methods are $4.7-7.8~M_\odot$, and $5.1-7.4~M_\odot$ respectively. Combining results of these two methods, we obtain a most probable mass range of the source to be $4.7-7.8~M_\odot$ or $6^{+1.8}_{-1.3}~M_\odot$.

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arXiv2016

Characterization of few transient black hole candidates during their X-ray outbursts with TCAF Solution

The theoretical concept of Chakrabarti-Titarchuk two Component Advective Flow (TCAF) model was introduced around two decade ago in mid-90s. Recently after the inclusion of TCAF model into XSPEC as an additive table model, we find that it is quite capable to fit spectra from different phases of few transient black hole candidates (TBHCs) during their outbursts. This quite agrees with our theoretical understanding. Here, a brief summary of our recent studies of spectral and temporal properties of few TBHCs during their X-ray outbursts with TCAF will be discussed.

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arXiv2016

Accretion Flow Dynamics of MAXI J1659-152 from the Spectral Evolution Study of its 2010 Outburst using the TCAF Solution

Transient black hole candidates are interesting objects to study in X-rays as these sources show rapid evolutions in their spectral and temporal properties. In this paper, we study the spectral properties of the Galactic transient X-ray binary MAXI~J1659-152 during its very first outburst after discovery with the archival data of RXTE Proportional Counter Array instruments. We make a detailed study of the evolution of accretion flow dynamics during its 2010 outburst through spectral analysis using the Chakrabarti-Titarchuk two-component advective flow (TCAF) model as an additive table model in XSPEC. Accretion flow parameters (Keplerian disk and sub-Keplerian halo rates, shock location and shock strength) are extracted from our spectral fits with TCAF. We studied variations of these fit parameters during the entire outburst as it passed through three spectral classes: hard, hard-intermediate, and soft-intermediate. We compared our TCAF fitted results with standard combined disk black body (DBB) and power-law (PL) model fitted results and found that variations of disk rate with DBB flux and halo rate with PL flux are generally similar in nature. There appears to be an absence of the soft state unlike what is seen in other similar sources.

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arXiv2016

Accretion flow dynamics of MAXI J1836-194 during its 2011 outburst from TCAF solution

The Galactic transient X-ray binary MAXI~J1836-194 was discovered on 29th August 2011. Here we make a detailed study of the spectral and timing properties of its 2011 outburst using archival data of RXTE Proportional Counter Array instrument. The evolution of accretion flow dynamics of the source during the outburst through spectral analysis with Chakrabarti-Titarchuk's two-component advective flow (TCAF) solution as a local table model in XSPEC. We also fitted spectra with combined disk blackbody and power-law models and compared it with the TCAF model fitted results. The source is found to be in hard and hard-intermediate spectral states only during entire phase of this outburst. No soft or soft-intermediate spectral states are observed. This could be due to the fact that this object belongs to a special class of sources (e.g., MAXI~J1659-152, Swift~J1753.5-0127, etc.) that have very short orbital periods and that companion is profusely mass-losing or the disk is immersed inside an excretion disk. In these cases, flows in the accretion disk is primarily dominated by low viscous sub-Keplerian flow and the Keplerian rate is not high enough to initiate softer states. Low-frequency quasi-periodic oscillations (QPOs) are observed sporadically although as in normal outbursts of transient black holes, monotonic evolutions of QPO frequency during both rising and declining phases are observed. From the TCAF fits, we find mass of the black hole in the range of $7.5-11~M_\odot$ and from time differences between peaks of the Keplerian and sub-Keplerian accretion rates we obtain viscous timescale for this particular outburst $\sim 10$~days.

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arXiv2015

Resonance Condition and Low Frequency Quasi Periodic Oscillations of the Outbursting Source H 1743-322

It has long been proposed that low frequency QPOs in stellar mass black holes or their equivalents in super massive black holes are results of resonances between infall and cooling time scales. We explicitly compute these two time scales in a generic situation to show that resonances are easily achieved. During an outburst of a transient black hole candidate (BHC), the accretion rate of the Keplerian disk as well as the geometry of the Comptonizing cloud change very rapidly. During some period, resonance condition between the cooling time scale (predominantly by Comptonization) and the infall time scale of the Comptonizing cloud is roughly satisfied. This leads to low frequency quasi-periodic oscillations (LFQPOs) of the Compton cloud and the consequent oscillation of hard X-rays. In this paper, we explicitly follow the BHC H 1743-322 during its 2010 outburst. We compute Compton cooling time and infall time on several days and show that QPOs take place when these two roughly agree within ~50%, i.e., the resonance condition is generally satisfied. We also confirm that for the sharper LFQPOs (i.e., higher Q-factors) the ratio of two time scales is very close to 1.

astro-ph.HE↗

arXiv2015

Characterization of GX 339-4 outburst of 2010-11: analysis by xspec using two component advective flow model

We study spectral properties of GX 339-4 during its 2010-11 outburst with Two Component Advective Flow (TCAF) model after its inclusion in XSPEC as a table model. We compare results fitted by TCAF model with combined disk black body and power-law model. For a spectral fit, we use 2.5-25 keV spectral data of the PCA instrument onboard RXTE satellite. From our fit, accretion flow parameters such as Keplerian (disk) rate, sub-Keplerian (halo) rate, location and strength of shock are extracted. We quantify how the disk and the halo rates vary during the entire outburst. We study how the halo to disk accretion rate ratio (ARR), quasi-periodic oscillations (QPOs), shock locations and its strength vary when the system passes through hard, hard-intermediate, soft-intermediate, and soft states. We find pieces of evidence of monotonically increasing and decreasing nature of QPO frequencies depending on the variation of ARR during rising and declining phases. Interestingly, on days of transition from hard state to hard-intermediate spectral state (during the rising phase) or vice-versa (during decline phase), ARR is observed to be locally maximum. Non-constancy of ARR while obtaining reasonable fits points to the presence of two independent components in the flow.

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arXiv2014

Is Compton cooling sufficient to explain evolution of observed quasi-periodic oscillations in Outburst sources?

In outburst sources, quasi-periodic oscillation (QPO) frequency is known to evolve in a certain way: in the rising phase, it monotonically goes up till a soft intermediate state is achieved. In the propagating oscillatory shock model, oscillation of the Compton cloud is thought to cause QPOs. Thus, in order to increase QPO frequency, Compton cloud must collapse steadily in the rising phase. In decline phases, exactly opposite should be true. We investigate cause of this evolution of the Compton cloud. The same viscosity parameter which increases the Keplerian disk rate, also moves the inner edge of the Keplerian component, thereby reducing the size of the Compton cloud and reducing the cooling time scale. We show that cooling of the Compton cloud by inverse Comptonization is enough for it to collapse sufficiently so as to explain the QPO evolution. In the Two Component Advective Flow (TCAF) configuration of Chakrabarti-Titarchuk, centrifugal force induced shock represents boundary of the Compton cloud. We take the rising phase of 2010 outburst of Galactic black hole candidate H~1743-322 and find an estimation of variation of $α$ parameter of the sub-Keplerian flow to be monotonically rising from $0.0001$ to $0.02$, well within the range suggested by magneto-rotational instability. We also estimate the inward velocity of the Compton cloud to be a few meters/second which is comparable to what is found in several earlier studies of our group by empirically fitting the shock locations with the time of observations.

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arXiv2014

Spectral signatures of dissipative standing shocks and mass outflow in presence of Comptonization around a black hole

Accretion flows having positive specific energy are known to produce outflows and winds which escape to a large distance. According to Two Component Advective Flow (TCAF) model, centrifugal pressure dominated region of the flow just outside the black hole horizon, with or without shocks, acts as the base of this outflow. Electrons from this region are depleted due to the wind and consequently, energy transfer rate due to inverse Comptonization of low energy photons are affected. Specifically, it becomes easier to cool this region and emerging spectrum is softened. Our main goal is to show spectral softening due to mass outflow in presence of Compton cooling. To achieve this, we modify Rankine-Hugoniot relationships at the shock front when post-shock region suffers mass loss due to winds and energy loss due to inverse Comptonization. We solve two-temperature equations governing an accretion flow around a black hole which include Coulomb exchange between protons and electrons and other major radiative processes such as bremsstrahlung and thermal Comptonization. We then compute emitted spectrum from this post-shock flow. We also show how location of standing shock which forms outer boundary of centrifugal barrier changes with cooling. With an increase in disc accretion rate $(\dot{m_d})$, cooling is enhanced and we find that the shock moves in towards the black hole. With cooling, thermal pressure is reduced, and as a result, outflow rate is decreased. We thus directly correlate outflow rate with spectral state of the disc.

astro-ph.HE↗

arXiv2014

Inference on accretion flow dynamics using TCAF solution from the analysis of spectral evolution of H 1743-322 during 2010 outburst

We study accretion flow dynamics of Galactic transient black hole candidate (BHC) H 1743-322 during its 2010 outburst by analyzing spectral data using Two Component (Keplerian and sub-Keplerian) Advective Flow (TCAF) solution, after its inclusion in XSPEC as a local model. We compare our TCAF solution fitted results with combined disk black body and power-law model fitted results and find a similar smooth variation of thermal (Keplerian or disk black body) and non-thermal (power-law or sub-Keplerian) fluxes/rates in two types of model fits. For a spectral analysis, 2.5-25 keV spectral data from RXTE PCA instrument are used. From the TCAF solution fit, accretion flow parameters, such as Keplerian rate, sub-Keplerian rate, location of centrifugal pressure supported shock and strength of the shock are extracted, thus providing a deeper understanding of accretion process and properties of accretion disks around BHC H 1743-322 during its X-ray outburst. Based on the halo to disk accretion rate ratio (ARR), shock properties, accretion rates and nature of quasi-periodic oscillations (QPOs, if observed) entire outburst is classified into four different spectral states, such as, hard, hard-intermediate, soft-intermediate, and soft. From time variation of intrinsic flow parameters it appears that their evolutions in decline phase do not retrace path of rising phase. Since our current model does not include magnetic fields, spectral turnover at energies beyond 500-600 keV cannot be explained.

astro-ph.HE↗

arXiv2014

Implementation of Two Component Advective Flow Solution in XSPEC

Spectral and Temporal properties of black hole candidates can be explained reasonably well using Chakrabarti-Titarchuk solution of two component advective flow (TCAF). This model requires two accretion rates, namely, the Keplerian disk accretion rate and the halo accretion rate, the latter being composed of a sub-Keplerian, low angular momentum flow which may or may not develop a shock. In this solution, the relevant parameter is the relative importance of the halo (which creates the Compton cloud region) rate with respect to the Keplerian disk rate (soft photon source). Though this model has been used earlier to manually fit data of several black hole candidates quite satisfactorily, for the first time, we made it user friendly by implementing it into XSPEC software of GSFC/NASA. This enables any user to extract physical parameters of the accretion flows, such as two accretion rates, the shock location, the shock strength etc. for any black hole candidate. We provide some examples of fitting a few cases using this model. Most importantly, unlike any other model, we show that TCAF is capable of predicting timing properties from the spectral fits, since in TCAF, a shock is responsible for deciding spectral slopes as well as QPO frequencies.

astro-ph.HE↗

arXiv2013

Evolution of the temporal and the spectral properties in 2010 and 2011 outbursts of H 1743-322

The Galactic black hole candidate H~1743-322 exhibited two X-ray outbursts in rapid succession: one in August 2010 and the other in April 2011. We analyze archival data of this object from the PCA instrument on board RXTE (2-25 keV energy band) to study the evolution of its temporal and spectral characteristics during both the outbursts, and hence to understand the behavioral change of the accretion flow dynamics associated with the evolution of the various X-ray features. We study the evolution of QPO frequencies during the rising and the declining phases of both the outbursts. We successfully fit the variation of QPO frequency using the Propagating Oscillatory Shock (POS) model in each of the outbursts and obtain the accretion flow parameters such as the instantaneous shock locations, the shock velocity and the shock strength. Based on the degree of importance of the thermal (disk black body) and the non-thermal (power-law) components of the spectral fit and properties of the QPO (if present), the entire profiles of the 2010 and 2011 outbursts are subdivided into four different spectral states: hard, hard-intermediate, soft-intermediate and soft. We attempt to explain the nature of the outburst profile (i.e., hardness-intensity diagram) with two different types of mass accretion flow.

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arXiv2013

Extracting Flow parameters of H 1743-322 during early phase of its 2010 outburst using Two Component Advective Flow model

We study the spectral properties of Galactic transient black hole candidate H 1743-322 during its early phase of 2010 outburst with Two Component Advective Flow (TCAF) model, after its inclusion in spectral analysis software package XSPEC as a local model. For the analysis, spectral data from RXTE/PCA instrument in 2.5-25 keV energy band are used. From the spectral fit, accretion flow parameters such as Keplerian (disk) rate, sub-Keplerian (halo) rate, location of the shock and strength of the shock are directly extracted. QPO frequencies are predicted from the TCAF model spectral fitted shock parameters, `closely' matches with the observed frequencies.

astro-ph.HE↗

arXiv2013

A comparative study of the timing and the spectral properties during two recent outbursts (2010 & 2011) of H 1743-322

The Galactic black hole candidate (BHC) H~1743-322 recently exhibited two outbursts in X-rays in August 2010 & April 2011. The nature (outburst profile, evolution of quasi-periodic oscillation (QPO) frequency and spectral states, etc.) of these two successive outbursts, which continued for around two months each, are very similar. We present the results obtained from a comparative study on the temporal and the spectral properties of the source during these two outbursts. The evolutions of QPOs observed in both the outbursts were well fitted with propagating oscillatory shock (POS) model. During both the outbursts, the observed spectral states (i.e, hard, hard-intermediate, soft-intermediate and soft) follow the `standard' type of hysteresis-loop, which could be explained with two component advective flow (TCAF) model.

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arXiv2013

Properties of the propagating oscillatory shock wave in the accretion flows around few transient black hole candidates during their outbursts

In our study of the timing properties of few Galactic black hole candidates evolutions of the low and intermediate frequency quasi-periodic oscillations (LIFQPOs) are observed. In 2005, for explaining evolution of QPO frequency during rising phase of 2005 GRO J1655-40 outburst, Chakrabarti and his students introduced a new model, namely propagating oscillatory shock (POS) model. Here we present the results obtained from the same POS model fitted QPO evolutions during both the rising and declining phases of the outbursts of 2005 GRO J165540, 2010-11 GX 339-4, and 2010 & 2011 H 1743-322.

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arXiv2012

Accretion flow dynamics during the evolution of timing and spectral properties of GX 339-4 during its 2010-11 outburst

The Galactic black-hole candidate GX 339-4 exhibited several outbursts at regular intervals of \sim 2-3 years in the Rossi X-ray Timing Explorer (RXTE) era. After remaining in an almost quiescent state for 3 years, it again became X-ray active in 2010 January, continuing to be so over the next \sim 14 months. We study the timing and spectral properties of the black hole candidate (BHC) during its recent outburst using RXTE PCA data, starting from 2010 January 12 to 2011 March 6. Our study provides a comprehensive understanding of the mass accretion processes and properties of the accretion disk of the black hole candidate. The PCA spectra of 2.5-25 keV are mainly fitted with a combination of two components, namely, a disk black body and a power-law. The entire outburst as observed by RXTE, is divided into 4 spectral states, namely, hard, hard-intermediate, soft-intermediate, and soft. Quasi-periodic oscillations (QPOs) were found in 3 out of the 4 states, namely hard, hard-intermediate, and soft-intermediate. The QPO frequencies increase monotonically from 0.102 Hz to 5.692 Hz in the rising phase of the outburst, while during the declining phase QPO frequencies decrease monotonically from 6.420 to 1.149 Hz. The recent outburst of GX 339-4 gives us an opportunity to understand the evolution of the two-component accretion rates starting from the onset to the end of the outburst phase. We found that the QPO frequency variation could be explained by the propagating oscillatory shock model (POS) and the hardness versus intensity variation can be reproduced if we assume that higher viscosity causes the conversion of a low angular momentum disk component into a Keplerian component during the outburst phase. The decline phase starts because of the reduction in the viscosity.

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arXiv2011

X-ray properties of the Sun and some compact objects of our Galaxy

In the Thesis, I study the X-ray properties of the two major stages of the life cycle of the stars: one is the normal life of a lighter mass star (Sun) and another is the collapsed state (black hole) of a star (black hole candidates GRO J1655-40, GX 339-4 and GRBs). I am lucky to be a team member for developing X-ray solar space instruments RT-2 (S, G and CZT) which observed both the Sun and Gamma-Ray Bursts (GRBs) from space. A part of my Thesis contains development of RT-2 instruments, characterization of CZT & CMOS imaging detectors (used in RT-2/CZT instrument), some observational results of solar flares and GRBs. My Thesis also contains the detailed timing & spectral properties of the 2005 outburst of the well known Galactic black hole candidate GRO J1655-40 and initial rising phase of 2010 outburst of the transient Galactic stellar mass black hole candidate GX 339-4.

astro-ph.HE↗