Sudip Bhattacharyya

Tata Institute of Fundamental Research

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Co-Authors

Tod E. Strohmayer

Goddard Space Flight Center

M. Coleman Miller

University of Maryland, College Park

Mayukh Pahari

Indian Institute of Technology Hyderabad

Chandrachur Chakraborty

Manipal Academy of Higher Education

Edward M. Cackett

Wayne State University

S. Chandra

Valeo (Ireland)

K. P. Singh

Tata Institute of Fundamental Research

J. M. Mïller

University of Michigan–Ann Arbor

A. A. Zdziarski

Polish Academy of Sciences

Yash Bhargava

Tata Institute of Fundamental Research

Cooperative Institutions

Centre National de la Recherche Scientifique

461

National Institute for Astrophysics

431

University of Turku

250

Institut d'Estudis Espacials de Catalunya

248

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

223

Universitat de Barcelona

210

TU Dortmund University

206

University of Łódź

189

University of Geneva

184

Max Planck Institute for Physics

181

Author Statistics

Papers

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Does the gravitomagnetic monopole exist? A clue from a black hole x-ray binary

Physical review. D/Physical review. D. (2018)

Chandrachur Chakraborty Sudip Bhattacharyya

The gravitomagnetic monopole is the proposed gravitational analogue of Dirac's magnetic monopole. However, an observational evidence of this aspect of fundamental physics was elusive. Here, we employ a technique involving three primary X-ray observational methods used to measure a black hole spin to search for the gravitomagnetic monopole. These independent methods give significantly different spin values for an accreting black hole. We demonstrate that the inclusion of one extra parameter due to the gravitomagnetic monopole not only makes the spin and other parameter values inferred from the three methods consistent with each other but also makes the inferred black hole mass consistent with an independently measured value. We argue that this first indication of the gravitomagnetic monopole, within our paradigm, is not a result of fine tuning.

Black hole (networking)

10.1103/physrevd.98.043021

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Citations (37)

Sensitivity of the Cherenkov Telescope Array to TeV photon emission from the Large Magellanic Cloud

Monthly Notices of the Royal Astronomical Society (2023)

A. Acharyya R. Adam Arnau Aguasca-Cabot I. Agudo Alejandra Aguirre-Santaella

ABSTRACT A deep survey of the Large Magellanic Cloud at ∼0.1–100 TeV photon energies with the Cherenkov Telescope Array is planned. We assess the detection prospects based on a model for the emission of the galaxy, comprising the four known TeV emitters, mock populations of sources, and interstellar emission on galactic scales. We also assess the detectability of 30 Doradus and SN 1987A, and the constraints that can be derived on the nature of dark matter. The survey will allow for fine spectral studies of N 157B, N 132D, LMC P3, and 30 Doradus C, and half a dozen other sources should be revealed, mainly pulsar-powered objects. The remnant from SN 1987A could be detected if it produces cosmic-ray nuclei with a flat power-law spectrum at high energies, or with a steeper index 2.3–2.4 pending a flux increase by a factor of >3–4 over ∼2015–2035. Large-scale interstellar emission remains mostly out of reach of the survey if its >10 GeV spectrum has a soft photon index ∼2.7, but degree-scale 0.1–10 TeV pion-decay emission could be detected if the cosmic-ray spectrum hardens above >100 GeV. The 30 Doradus star-forming region is detectable if acceleration efficiency is on the order of 1−10 per cent of the mechanical luminosity and diffusion is suppressed by two orders of magnitude within <100 pc. Finally, the survey could probe the canonical velocity-averaged cross-section for self-annihilation of weakly interacting massive particles for cuspy Navarro–Frenk–White profiles.

Cherenkov Telescope Array

Large Magellanic Cloud

Spectral index

10.1093/mnras/stad1576

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Contrasting X-ray/UV time-lags in Seyfert 1 galaxies NGC 4593 and NGC 7469 usingAstroSatobservations

Monthly Notices of the Royal Astronomical Society (2023)

Kavita Kumari G. C. Dewangan I. E. Papadakis Max W J Beard I. M. McHardy

ABSTRACT We study accretion disc–corona connection in Seyfert 1 galaxies using simultaneous UV/X-ray observations of NGC 4593 (2016 July 14–18) and NGC 7469 (2017 October 15–19) performed with AstroSat. We use the X-ray (0.5–7.0 keV) data acquired with the Soft X-ray Telescope (SXT) and the UV (FUV: 130–180 nm, NUV: 200–300 nm) data obtained with the Ultra-Violet Imaging Telescope (UVIT). We also use the contemporaneous Swift observations of NGC 4593 and demonstrate AstroSat’s capability for X-ray/UV correlation studies. We performed UV/X-ray cross-correlation analysis using the interpolated and the discrete cross-correlation functions and found similar results. In the case of NGC 4593, we found that the variations in the X-rays lead to those in the FUV and NUV bands by ∼38 ks and ∼44 ks, respectively. These UV lags favour the disc-reprocessing model; they are consistent with the previous results within uncertainties. In contrast, we found an opposite trend in NGC 7469 where the soft X-ray variations lag those in the FUV and NUV bands by ∼41 ks and ∼49 ks, respectively. The hard lags in NGC 7469 favour the thermal Comptonization model. Our results may provide direct observational evidence for the variable intrinsic UV emission from the accretion disk, which acts as the seed for thermal Comptonization in a hot corona in a lamp-post-like geometry. The non-detection of disk reverberation photons in NGC 7469, using AstroSat data, is most likely due to a high accretion rate resulting in a hot accretion disc and large intrinsic emission.

Hubble sequence

10.1093/mnras/stad755

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Disk-corona modeling for spectral index and luminosity correlation of tidal disruption events

Physical review. D/Physical review. D. (2023)

T. Mageshwaran Sudip Bhattacharyya

We present a relativistic disk-corona model for a steady state advective accretion disk to explain the UV to x-ray spectral index ${\ensuremath{\alpha}}_{\mathrm{OX}}$ evolution of four tidal disruption event (TDE) sources XMMSL2J1446, XMMSL1J1404, XMMSL1J0740, and AT2018fyk. The viscous stress in our model depends on gas (${P}_{g}$) and total (${P}_{t}$) pressures as ${\ensuremath{\tau}}_{r\ensuremath{\phi}}\ensuremath{\propto}{P}_{g}^{\ensuremath{\mu}}{P}_{t}^{1\ensuremath{-}\ensuremath{\mu}}$, where $\ensuremath{\mu}$ is a constant. We compare various steady and time-dependent sub-Eddington TDE accretion models along with our disk-corona model to the observed ${\ensuremath{\alpha}}_{\mathrm{OX}}$ of TDE sources and find that the disk-corona model agrees with the observations better than the other models. We find that $\ensuremath{\mu}$ is much smaller than unity for TDE sources XMMSL2J1446, XMMSL1J1404, and XMMSL1J0740. We also compare the relativistic model with a nonrelativistic disk-corona model. The relativistic accretion dynamics reduce the spectral index relative to the nonrelativistic accretion by increasing the energy transport to the corona. We estimate the mass accretion rate for all the sources and find that the observed luminosity follows a nearly linear relation with the mass accretion rate. The ratio of x-ray luminosity from the disk to the corona increases with the mass accretion rate. The observed ${\ensuremath{\alpha}}_{\mathrm{OX}}$ shows positive and negative correlations with luminosity. The disk-corona model explains the negative correlation seen in the TDE sources XMMSL1J0740, XMMSL2J1446, and XMMSL1J1404. However, TDE AT2018fyk shows a positive correlation at higher luminosity and shows a better fit when a simple spherical adiabatic outflow model is added to the relativistic disk-corona model. Even though the disk luminosity dominates at a higher mass accretion rate, we show that the accretion models without a corona are unable to explain the observations, and the presence of a corona is essential.

Corona (planetary geology)

Spectral index

10.1103/physrevd.107.103036

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A Study of a Tilted Thin Inner Accretion Disk around a Spinning Black Hole

The Astrophysical Journal (2019)

Srimanta Banerjee Chandrachur Chakraborty Sudip Bhattacharyya

Abstract The inner part of a thin accretion disk around a Kerr black hole can serve as an important tool to study the physics of the strong gravity regime. A tilt in such a disk with respect to the black hole spin axis is particularly useful for this purpose, as such a tilt can have a significant effect on the observed X-ray spectral and timing features via Lense–Thirring precession. However, the inner disk has been predicted to become aligned with the spin direction of the black hole by the well-known Bardeen–Petterson effect. Here we calculate, both analytically and numerically, the radial profile of the thin accretion disk tilt angle in the viscous regime (i.e., α is the Shakura–Sunyaev viscosity parameter, H is the disk thickness, and R is the radial distance). We show that the inner disk may not be aligned at all for certain reasonable ranges of parameter values. This makes the inner accretion disk particularly promising to probe the black hole parameters, and the accretion process in the strong gravity region.

Thin disk

Accretion disc

Precession

Black hole (networking)

Intermediate polar

Thick disk

10.3847/1538-4357/aaf102

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Citations (11)

AstroSat and Chandra View of the High Soft State of 4U 1630–47 (4U 1630–472): Evidence of the Disk Wind and a Rapidly Spinning Black Hole

The Astrophysical Journal (2018)

Mayukh Pahari Sudip Bhattacharyya A. R. Rao D. Bhattacharya S. Vadawale

We present the X-ray spectral and timing analysis of the transient black hole X-ray binary 4U 1630-47, observed with the AstroSat, Chandra and MAXI space missions during its soft X-ray outburst in 2016. The outburst, from the rising phase until the peak, is neither detected in hard X-rays (15-50 keV) by the Swift/BAT nor in radio. Such non-detection along with the source behavior in the hardness-intensity and color-color diagrams obtained using MAXI data confirm that both Chandra and AstroSat observations were performed during the high soft spectral state. The High Energy Grating (HEG) spectrum from the Chandra high-energy transmission grating spectrometer (HETGS) shows two strong, moderately blueshifted absorption lines at 6.705$_{-0.002}^{+0.002}$ keV and 6.974$_{-0.003}^{+0.004}$ keV, which are produced by Fe XXV and Fe XXVI in a low-velocity ionized disk wind. The corresponding outflow velocity is determined to be 366$\pm$56 km/s. Separate spectral fits of Chandra/HEG, AstroSat/SXT+LAXPC and Chandra/HEG + AstroSat/SXT+LAXPC data show that the broadband continuum can be well described with a relativistic disk-blackbody model, with the disk flux fraction of $\sim 0.97$. Based on the best-fit continuum spectral modeling of Chandra, AstroSat and Chandra+AstroSat joint spectra and using the Markov Chain Monte Carlo simulations, we constrain the spectral hardening factor at 1.56$^{+0.14}_{-0.06}$ and the dimensionless black hole spin parameter at 0.92 $\pm$ 0.04 within the 99.7% confidence interval. Our conclusion of a rapidly-spinning black hole in 4U 1630-47 using the continuum spectrum method is in agreement with a previous finding applying the reflection spectral fitting method.

Black hole (networking)

Black-body radiation

Dimensionless quantity

10.3847/1538-4357/aae53b

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Citations (19)

On the Origin of Broad Iron Lines in Neutron Star Low-mass X-ray Binaries

arXiv (Cornell University) (2015)

Chia-Ying Chiang Edward M. Cackett J. M. Mïller D. Barret Andy Fabián

Broad Fe K emission lines have been widely observed in the X-ray spectra of black hole systems, and in neutron star systems as well. The intrinsically narrow Fe K fluorescent line is generally believed to be part of the reflection spectrum originating in an illuminated accretion disk, and broadened by strong relativistic effects. However, the nature of the lines in neutron star LMXBs has been under debate. We therefore obtained the longest, high-resolution X-ray spectrum of a neutron star LMXB to date with a 300 ks Chandra HETGS observation of Serpens X-1. The observation was taken under the continuous clocking mode and thus free of photon pile-up effects. We carry out a systematic analysis and find that the blurred reflection model fits the Fe line of Serpens X-1 significantly better than a broad Gaussian component does, implying that the relativistic reflection scenario is much preferred. Chandra HETGS also provides highest spectral resolution view of the Fe K region and we find no strong evidence for additional narrow lines.

Serpens

Reflection

Line (geometry)

X-ray binary

Accretion disc

Low Mass

Symbiotic star

Source

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Neutron Star Physics in the Square Kilometre Array Era: An Indian Perspective

Journal of Astrophysics and Astronomy (2016)

Sushan Konar Manjari Bagchi Debades Bandyopadhyay Sarmistha Banik D. Bhattacharya

10.1007/s12036-016-9409-6

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Citations (18)

General Relativistic Spectra of Accretion Disks around Rotating Neutron Stars

The Astrophysical Journal (2001)

Sudip Bhattacharyya Ranjeev Misra Arun V. Thampan

General relativistic spectra from accretion disks around rotating neutron stars in the appropriate spacetime geometry for several different equations of state, spin rates, and masses of the compact object have been computed. The analysis involves the computation of the relativistically corrected radial temperature profiles and the effect of Doppler and gravitational redshifts on the spectra. Light-bending effects have been omitted for simplicity. The relativistic spectrum is compared with the Newtonian one, and it is shown that the difference between the two is primarily a result of the different radial temperature profiles for the relativistic and Newtonian disk solutions. To facilitate direct comparison with observations, a simple empirical function has been presented which describes the numerically computed relativistic spectra well. This empirical function (which has three parameters including normalization) also describes the Newtonian spectrum adequately. Thus, the function can in principle be used to distinguish between the two. In particular, the best-fit value of one of the parameters (β-parameter) ≈0.4 for the Newtonian case, while it ranges from 0.1 to 0.35 for the relativistic case depending upon the inclination angle, equation of state (EOS), spin rate, and mass of the neutron star. Constraining this parameter by fits to future observational data of X-ray binaries will indicate the effect of strong gravity in the observed spectrum.

Relativistic quantum chemistry

Relativistic beaming

Compact star

10.1086/319807

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Citations (32)

Science with the $AstroSat$ Soft X-ray Telescope: an overview

arXiv (Cornell University) (2021)

Sudip Bhattacharyya K. P. Singh Gordon Stewart S. Chandra G. C. Dewangan

The Soft X-ray Telescope (SXT) aboard the $AstroSat$ satellite is the first Indian X-ray telescope in space. It is a modest size X-ray telescope with a charge coupled device (CCD) camera in the focal plane, which provides X-ray images in the $\sim 0.3-8.0$ keV band. A forte of SXT is in providing undistorted spectra of relatively bright X-ray sources, in which it excels some current large CCD-based X-ray telescopes. Here, we highlight some of the published spectral and timing results obtained using the SXT data to demonstrate the capabilities and overall performance of this telescope.

X-ray telescope

Spitzer Space Telescope

Optical telescope

Charge-coupled device

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