Anuj Nandi

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

Context. The Galactic transient black hole candidate (BHC) GX 339-4 exhibited several outbursts at regular intervals of about two to three years in the Rossi X-ray Timing Explorer (RXTE) era. After remaining in an almost quiescent state for three long years, it again became X-ray active in January, 2010, continuing to be so over the next ∼14 months. Aims. We study the timing and spectral properties of the BHC during its recent outburst and understand the behavioral change in the accretion flow dynamics associated with the evolution of the various X-ray features. Methods. The detailed analysis of the temporal and spectral properties of the source during this outburst are carried out using archival data of the RXTE PCA instrument. We analyze a total of 236 observational intervals consisting of 419 days of data observed by RXTE, from 2010 January 12 to 2011 March 6. Results. Our study provides a comprehensive understanding of the mass accretion processes and properties of the accretion disk of the BHC. 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 four spectral states, namely, hard, hard-intermediate, softintermediate, and soft. Quasi-periodic oscillations (QPOs) were found in three out of the four states, namely hard, hard-intermediate, and soft-intermediate states. 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 evolution pattern, i.e. the hardness-intensity diagram, of the present outburst can be reproduced by two different components of the flow of accreting material. Conclusions. 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.

Computation of outflow rates from accretion disks around black holes

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 Keplerian matter supplies soft-photons, hot sub-Keplerian matter supplies thermal electrons. The temperature of the hot electrons is decided by the degree of inverse Comptonization of the soft photons. If we consider only thermally-driven flows from the centrifugal pressure-supported boundary layer around a black hole, we find that when the thermal electrons are cooled down, either because of the absence of the boundary layer (low compression ratio), or when the surface of the boundary layer is formed very far away, the outflow rate is negligible. For an intermediate size of this boundary layer the outflow rate is maximal. Since the temperature of the thermal electrons also decides the spectral state of a black hole, we predict that the outflow rate should be directly related to the spectral state.

Properties of the propagating shock wave in the accretion flow around GX 339-4 in the 2010 outburst

Context. The black hole candidate GX 339-4 exhibited an X-ray outburst in January 2010, which is still continuing. We here discuss the timing and the spectral properties of the outburst using RXTE data. Aims. Our goal is to study the timing and spectral properties of GX 339-4 using its recent outburst data and extract information about the nature of the accretion flow. Methods. We use RXTE archival data of the recent GX 339-4 outburst and analyze them with the NASA HEAsoft package, version 6.8. We then compare the observed quasi-periodic oscillation (QPO) frequencies with those from existing shock oscillation model and obtain the nature of evolution of the shock locations during the outburst. Results. We found that the QPO frequencies are monotonically increasing from 0.102 Hz to 5.69 Hz within a period of ~ 26 days. We explain this evolution with the propagating oscillatory shock (POS) solution and find the variation of the initial and final shock locations and strengths. The model fits also give the velocity of the propagating shock wave, which is responsible for the generation of QPOs and their evolutions, at ~ 10 m/s. We observe from the spectra that up to 2010 April 10, the object was in a hard state. After that, it went to the hard-intermediate state. On April 18, it had a state transition and went to the soft-intermediate state. On May 15, another state transition was observed and the source moved to the soft state. Conclusions. As in the previously fitted outburst sources, this source also showed the tendency of a rapidly increasing QPO frequency (

Periodic mass loss from viscous accretion flows around black holes

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DETERMINATION OF THE MASS OF IGR J17091-3624 FROM ``SPECTRO-TEMPORAL'' VARIATIONS DURING THE ONSET PHASE OF THE 2011 OUTBURST

) in a viscous time scale, which can be modeled quite accurately. In this case, the shock seems to have disappeared at about ~ 172 Schwarzschild radii, unlike in the 2005 outburst of GRO J1655-40, where the shock disappeared behind the horizon.

SWIFT view of the 2015 outburst of GS 2023+338 (V404 Cyg): complex evolution of spectral and temporal characteristics

We investigate the behaviour of low angular momentum viscous accretion flows around black holes using smooth particle hydrodynamics method. Earlier, it has been observed that in a significant part of the energy and angular momentum parameter space, rotating transonic accretion flow undergoes shock transition before entering in to the black hole and a part of the post-shock matter is ejected as bipolar outflows, which are supposed to be the precursor of relativistic jets. In this work, we simulate accretion flows having injection parameters from the inviscid shock parameter space, and study the response of viscosity on them. With the increase of viscosity, shock becomes time dependent and starts to oscillate when the viscosity parametercrossesitscriticalvalue.Asaresult,theinfallingmatterinsidethepost-shockregion exhibits quasi-periodic variations and causes periodic ejection of matter from the inner disc as outflows. In addition, the same hot and dense post-shock matter emits high energy radiation

Mass loss from advective accretion disc around rotating black holes

The 2011 outburst of the black hole candidate IGR J17091-3624 followed the canonical track of state transitions along with the evolution of Quasi-Periodic Oscillation (QPO) frequencies before it began exhibiting various variability classes similar to GRS 1915+105. We use this canonical evolution of spectral and temporal properties to determine the mass of IGR J17091-3624, using three different methods, viz : Photon Index (

DETECTION OF GRB 090618 WITH THE RT-2 EXPERIMENT ON BOARD THE CORONAS-PHOTON SATELLITE

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Evidence of Class Transitions in GRS 1915+105 from Indian X-Ray Astronomy Experiment Data

) - QPO frequency (

Instruments of RT-2 experiment onboard CORONAS-PHOTON and their test and evaluation III: Coded Aperture Mask and Fresnel Zone Plates in RT-2/CZT payload

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