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Transonic Accretion and Winds Around Pseudo-kerr Black Holes And Comparison with General Relativistic Solutions

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Research in Astronomy and Astrophysics 2022年第3期22卷 157-167页

作者： Abhrajit Bhattacharjee sandip k.chakrabarti Dipak Debnath Indian Centre for Space Physics 43 ChalantikaGaria Station RoadKolkata 700084India

Spectral and timing properties of accretion flows on a black hole depend on their density and temperature distributions,which in turn come from the underlying ***,an accurate description of the flow which includes hydrodynamics and radiative transfer is a must to interpret the observational *** the case of nonrotating black holes,a pseudo-Newtonian description of surrounding spacetime enables one to make significant progress in predicting spectral and timing *** formalism is lacking for spinning black *** this paper,we show that there exists an exact form of a"natural"potential derivable from the general relativistic(GR)radial momentum *** of this potential in an otherwise Newtonian set of equations allows to describe transonic flows very accurately as is evidenced by comparing with solutions obtained from the full GR *** study the properties of the critical points and the centrifugal pressure supported shocks in the parameter space spanned by the specific energy and angular momentum,and compare with the results of GR *** show that this potential can safely be used for the entire range of kerr parameter-1k *** assume the flow to be ***,it is non-dissipative with constant energy and angular *** assumptions are valid very close to the black hole as the infall timescale is much shorter as compared to the viscous timescale.

关键词： black hole physics(159) kerr black holes(886) relativity(1393) hydrodynamics(1963) shocks(2086)

Spectral analysis of χ class data of GRS 1915+105 using TCAF solution

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Research in Astronomy and Astrophysics 2020年第12期20卷 347-356页

作者： Anuvab Banerjee Ayan Bhattacharjee Dipak Debnath sandip k.chakrabarti S.N.Bose National Centre for Basic Sciences Block-JDSector-3Salt LakeKolkata700106India Indian Centre for Space Physics 43 ChalantikaGaria St.Rd.Kolkata700084India

The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency(CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentum keplerian flow in the form of a radiatively efficient disk and a low angular momentum radiatively inefficient sub-keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χsubclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow(TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF *** the same time, the normalization required by this model along with the variation of photon index and exponent

关键词： X-Rays:binaries stars:individual(GRS 1915+105) stars:black holes accretion,accretion disks ISM:jets and outflows radiation:dynamics

Accretion flow properties of XTE J1118+480 during its 2005 outburst

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Research in Astronomy and Astrophysics 2020年第11期20卷 222-230页

作者： Dipak Debnath Debjit Chatterjee Arghajit Jana sandip k.chakrabarti kaushik Chatterjee Indian Centre for Space Physics 43 ChalantikaGaria St.Rd.Kolkata700084India Physical Research Laboratory NavrangpuraAhmedabad 380009India

We study spectral and temporal properties of Galactic short orbital period transient black hole XTE J1118+480 during its 2005 outburst using archival data of RXTE PCA and HEXTE instruments in the combined energy range of 3−100 *** analysis with the physical two component advective flow(TCAF)model allows us to understand the accretion flow properties of the *** found that this outburst of XTE J1118+480 is an unconventional outburst as the source was only in the hard state(HS).Our spectral analysis suggests that during the entire outburst,the source was highly dominated by the low angular momentum sub-keplerian halo *** the source was active in radio throughout the outburst,we make an effort to estimate X-ray contribution of jets to total observed X-ray emissions from the spectral analysis with the TCAF *** total X-ray intensity shows a similar nature of evolution as that of radio and jet X-ray *** allowed us to define this‘outburst’also as a jet dominated‘outburst’.Total X-ray flux is also found to subside when jet activity *** detailed spectral analysis also indicated that although the source was only in the HS during the outburst,in the late declining phase the spectrum became slightly softer due to the slow rise in the keplerian disk rate.

关键词： X-Rays binaries-stars black holes-stars individual (XTE J1118+480)-accretion,accretion disks-ISM jets and outflows-radiation dynamics

Inference on disk-jet connection of MAXI J1836–194 from spectral analysis with the TCAF solution

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Research in Astronomy and Astrophysics 2020年第3期20卷 28-41页

作者： Arghajit Jana Dipak Debnath sandip kchakrabarti Debjit Chatterjee Indian Centre for Space Physics 43 ChalantikaGaria St.Rd.Kolkata700084India

Galactic transient black hole candidate(BHC)MAXI J1836–194 was discovered on 2011 Aug30,by MAXI/GSC and Swift/*** source activity during this outburst continued for^3 months before entering into the quiescent *** again became active in March 2012 and continued for another^2 *** this paper,3-25 keV RXTE/PCA spectra from the 2011 outburst and 0.5-10.0 keV Swift/XRT data during its 2012 outburst are analyzed with the two-component advective flow(TCAF)model based fits files in *** calculate the X-ray contributions coming from jets/outflow using a newly developed method based on the deviation of the TCAF model *** also study the correlation between observed radio and estimated jet X-ray *** correlation indices(b)are found to be 1.79 and 0.61,when the 7.45 GHz Very Large Array(VLA)radio flux is correlated with the total X-ray and jet X-ray fluxes in 3-25 keV range *** has been found that the jet contributes in X-rays up to a maximum of 86%during its 2011 *** makes the BHC MAXI J1836–194 strongly jet dominated during the initial rising phase.

关键词： X-Rays:binaries stars individual:(MAXI J1836–194) stars:black holes accretion,accretion disks ISM:jets and outflows radiation:dynamics

Accretion properties of MAXI J1813-095 during its failed outburst in 2018

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Research in Astronomy and Astrophysics 2021年第5期21卷 235-246页

作者： Arghajit Jana Gaurava k.Jaisawal Sachindra Naik Neeraj kumari Debjit Chatterjee kaushikChatterjee Riya Bhowmick sandip kchakrabarti Hsiang-kuang Chang Dipak Debnath Astronomy&Astrophysics Division Physical Research LaboratoryNavrangpuraAhmedabad 380009India National Space Institute Technical University of DenmarkElektrovej327-328DK-2800 LyngbyDenmark High Energy Astrophysics Indian Centre for Space PhysicsGaria St RoadKolkata 700084India Department of Physics Indian Institute of TechnologyGandhinagar 382355GujaratIndia Indian Institute of Astrophysics KoramangalaBangalore 560034India Department of Physics “National Tsing Hua University”Hsinchu 30013China

We present the results obtained from detailed timing and spectral studies of a black hole candidate MAXI J1813-095 using Swift,NICER,and NuSTAR observations during its 2018 *** timing behavior of the source is mainly studied by examining NICER light curves in the 0.5−10 keV *** did not find any signature of quasi-periodic oscillations in the power density spectra of the *** carry out spectral analysis with a combined disk blackbody&power law model,and physical two-component advective flow(TCAF)*** the combined disk blackbody&power-law model,we extracted thermal and non-thermal fluxes,photon index and inner disk *** also find evidence for weak reflection in the *** have tested the physical TCAF model on a broadband spectrum from NuSTAR and Swift/*** parameters like mass accretion rates,the size of Compton clouds and the shock strength are *** result affirms that the source remained in the hard state during the entire outburst which indicates a‘failed’*** estimate the mass of the black hole as 7.4±1.5M⊙from the spectral study with the TCAF *** apply the LAOR model for the Fe k line *** this,the spin parameter of the black hole is ascertained as a^(∗)>*** inclination angle of the system is estimated to be in the range of 28°−45°from the reflection *** find the source distance to be∼6 kpc.

关键词： X-Rays:binaries stars individual:(MAXI J1813-095) stars:black holes accretion,accretion disks–shock waves radiation:dynamics

Hydro-chemical study of the evolution of interstellar pre-biotic molecules during the collapse of molecular clouds

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Research in Astronomy and Astrophysics 2012年第12期12卷 1613-1624页

作者： Liton Majumdar Ankan Das sandip k. chakrabarti Sonali chakrabarti Indian Centre for Space Physics Chalantika 43Garia Station RoadKolkata-700084India S.N.Bose National Centre for Basic Sciences Salt LakeKolkata-700098India Maharaja Manindra Chandra College 20 Ramakanto Bose StreetKolkata-700003India

One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge about the rate coefficients of various reactions which take place in the interstellar medium and molecular *** theoretical models of rate coefficients do exist in the literature for computing abundances of complex pre-biotic *** far these have been used to study the abundances of these molecules in ***,in order to obtain more accurate final compositions in these media,we have calculated the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical *** use these rates inside our hydro-chemical model to examine the chemical evolution and final abundances of pre-biotic species during the collapsing phase of a *** find that a significant amount of various pre-biotic molecules could be produced during the collapse phase of a *** thoroughly study the formation of these molecules via successive neutral-neutral and radical-radical/radicalmolecular *** present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud. We compare the formation of adenine in interstellar space using our rate-coefficients and using those obtained from existing theoretical *** routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the *** presence of grains strongly affects the abundances of the gas phase *** also carry out a comparative study between different pathways available for the synthesis of adenine,alanine, glycine and other molecules considered in our *** the huge abundances of the neutral reactive species,production of adenine is found to be strongly dominated by the radical-radical/radical-molecular reaction *** all the reactio

关键词： ISM clouds-astrochemistry-stars formation

Unusual Change in Critical Frequency of F<sub>2</sub>Layer during and Prior to Earthquakes

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Open Journal of Earthquake Research 2017年第4期6卷 191-203页

作者： Soujan Ghosh Sudipta Sasmal Subrata kumar Midya sandip k. chakrabarti Indian Centre for Space Physics Kolkata India Department of Atmospheric Sciences Calcutta University Kolkata India S. N. Bose National Centre for Basic Sciences Kolkata India

The unusualness in the critical frequency of different layers of earth’s ionosphere is commensurate to be associated with seismic events. We present study of critical frequency of F2 layer (denoted as f0F2) during some major earthquakes in South American region. We use the semi-empirical Barbier’s theorem of air-glow and define a parameter using the critical frequency and virtual height of F2 layer and named it as “F Parameter”. To investigate the variation of this parameter, we consider five large earthquakes in the junction of Nazca plate and South American plate having magnitude greater than M > 6.5 and study the temporal variation of F parameter during these earthquakes. The F Parameter is measured using the ionograms as recorded from the Ionosonde in Jicamarca Radio Observatory (lat. 11.95°S, long 76.87°W) in Chile which lies within the earthquake preparation zones of these five earthquakes. We examine the F Parameter within a span of ±15 days during earthquakes and observed significant change in the evaluated F Parameter in 12 to 3 days prior to the earthquakes. The increment is over +3σ from the normal variation. We also observe significant changes during aftershock events. The solar geomagnetic indices were found to be low which ensures that these anomalies in F Parameter are due to seismic events.

关键词： Earthquake Early Warning Wave Propagation Earthquake Interaction Forecasting and Prediction Ionosphere/Atmosphere Interactions Electrical Properties

Contaminated Effect of Geomagnetic Storms on Pre-Seismic Atmospheric and Ionospheric Anomalies during Imphal Earthquake

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Open Journal of Earthquake Research 2020年第5期9卷 383-402页

作者： Sagardweep Biswas Subrata kundu Soujan Ghosh Swati Chowdhury Shih-Sian Yang Masashi Hayakawa Suman Chakraborty sandip k. chakrabarti Sudipta Sasmal Indian Centre for Space Physics Kolkata India Institute of Space Science National Central University Chinese Taipei Hayakawa Institute of Seismo Electromagnetics Co. Ltd. UEC Alliance Center Chofu Tokyo Japan Physical Research Laboratory Navrangpura Ahmedabad India

Study of seismo-ionospheric coupling mechanism demands the quiet geomagnetic condition to eliminate any kind of contamination in the lower atmospheric and ionospheric parameters. In this manuscript, we present the effect of back to back two geomagnetic storms before a strong earthquake happened in Imphal, India on January 4, 2016 (M = 6.7). We studied the lower ionospheric irregularities for the duration of 31 days by computing the nighttime fluctuations in Very Low Frequency (VLF) radio signal received transmitter JJI (22.2 kHz) in Japan at Ionospheric and Earthquake Research Centre & Optical Observatory (IERCOO), Sitapur, India. We also studied the presence of Atmospheric Gravity Wave (AGW) in nighttime VLF signal in lower ionospheric heights and the same computed that from SABER/TIMED satellite. Two geomagnetic storms occurred on December 21, and 31, 2015. By the conventional analysis, we found that there is a significant decrease in nighttime trend and an increase in nighttime fluctuations around 15 days before the earthquake and just on the first storm and thus the pre-seismic effects on VLF signal gets contaminated due to the presence of storms. The wave-like structure in VLF fluctuations shows significant increase in intensity by using Fourier and Wavelet analysis before the earthquake. By analysis of SABER data, we found significant enhancement in AGW around 10 days before the earthquake. As the wavelike structures are coming from neutral acoustics reasons from pressure or temperature variations, this paper exhibits a significant example of contamination in ionospheric parameters due to geomagnetic storm where the acoustics parameters remain un-contaminated.

关键词： Very Low Frequency Wave Propagation Earthquake Precursory Atmospheric Gravity Wave Geomagnetic Strom SABER/TIMED