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Papers by BIKASH CHANDRA PAUL

Research paper thumbnail of Revisiting SW J2000.6+3210: a persistent Be X-ray pulsar?

Monthly Notices of the Royal Astronomical Society, 2013

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Research paper thumbnail of Models of compact objects with charge in generalized Tolman-Kuchowicz metric

Astrophysics and Space Science

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Research paper thumbnail of NUSTAR and Swift observations of AMXP Swift J1756.9−2508 during its 2018 outburst

Monthly Notices of the Royal Astronomical Society, Oct 3, 2019

ABSTRACT We present here the timing and spectral analysis of the accreting millisecond pulsar (AM... more ABSTRACT We present here the timing and spectral analysis of the accreting millisecond pulsar (AMXP) SwiftJ1756.9−2508 during its recent outburst in 2018 using Swift and NUSTAR observations. The simultaneous fitting of the Swift and NUSTAR spectra indicates that the source was in the hard state with a cut-off energy of about 74.58 keV. We also study in detail the pulse profile of the AMXP and its dependence on energy. The colour–colour diagram of the source is different from those previously reported. We performed phase- and time-resolved spectral analysis using NUSTAR data. Pulse phase-resolved spectra were fitted with a power-law model and significant changes in the spectral parameters with pulse phase were observed. The orbital phase and time-resolved spectra were fitted with a cut-off power-law model. The column density and photon index obtained from orbital phase spectral analysis were found to show some anticorrelation with the flux. Through time-resolved spectral analysis, we observed that the spectral parameters show positive correlation with each other and with the flux. We do not observe a softening of the spectrum with time. No emission lines or Compton bump were observed in the spectrum of the AMXP.

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Research paper thumbnail of Modified Chaplygin gas and constraints on its<i>B</i>parameter from cold dark matter and unified dark matter energy cosmological models

Monthly Notices of the Royal Astronomical Society, Aug 21, 2009

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Research paper thumbnail of Nonsingular Black Holes in Higher dimensions

arXiv (Cornell University), 2023

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Research paper thumbnail of Inflation in Bianchi models and the cosmic no-hair theorem

Physical review, Nov 27, 2001

ABSTRACT

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Research paper thumbnail of Chaotic Inflationary Universe in Rastall Gravity

Canadian Journal of Physics, Jun 23, 2023

We study Linde’s chaotic inflation in Rastall gravity with a homogeneous scalar field. In Einstei... more We study Linde’s chaotic inflation in Rastall gravity with a homogeneous scalar field. In Einstein’s general theory of relativity, Linde obtained chaotic scenario, which emerged from chaotic distribution of scalar field satisfying a limiting value of the initial scalar field ϕo &gt; 3 MP that lies in the quantum gravity. The upper limit on the initial scalar field is obtained for a sufficient inflation to encompass the present universe. In the Rastall gravity, the upper limit is reduced depending on the Rastall parameter γ &lt; 1. The upper limit on ϕo is found to increases for [Formula: see text]. In the later case, sufficient inflation is not permitted and the role of curvaton field is explored for an acceptable early chaotic inflation.

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Research paper thumbnail of Relativistic strange stars with anisotropy and B-parameter in pseudo spheroidal space time

Proceedings of the International Astronomical Union, Aug 1, 2012

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Research paper thumbnail of Power Law Inflation and the Cosmic No Hair Theorem in Brane World

Nucleation and Atmospheric Aerosols, 2006

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Research paper thumbnail of Observational constraints on modified Chaplygin gas in Horava–Lifshitz gravity with dark radiation

Pramana, Sep 28, 2013

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Research paper thumbnail of Can extended Chaplygin gas source a Hubble tension resolved emergent universe ?

arXiv (Cornell University), Jul 5, 2023

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Research paper thumbnail of An Introduction to Astronomical Data Analysis

The edited book contains seven chapters containing pedagogical approach of analysis of astronomic... more The edited book contains seven chapters containing pedagogical approach of analysis of astronomical and cosmological data. Cosmology is the study of the cosmos. Present decade is witnessing a transition of cosmology from a speculative science to an experimental science. A number of observational missions in the space in recent times lead to take up experiments and collect data that are pouring from last scattering surface of the sky in addition to stellar data. The advancement of science and technology made it possible to peep deep into the sky and consequently number of new phenomenon are captured by the detectors placed high up in the sky including terrestrial telescope. In this connection an introductory data analysis workshop organized at IUCAA Resource Centre, Physics Department, North Bengal University (NBU), India. It was felt that a write up will help the researchers for their data analysis with the observed data. Prof. D. Fraix-Burnet from France and other scientists from India discussed the method of data analysis and how to handle huge amount of data. This book is the outcome of the IUCAA sponsored workshop held at NBU.

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Research paper thumbnail of Brane World Inflation with Scalar and Tachyon Fields

arXiv (Cornell University), Aug 7, 2007

We present inflationary models of the early universe in the braneworld scenario considering both ... more We present inflationary models of the early universe in the braneworld scenario considering both scalar field and tachyon field separately. The technique of Chervon and Zhuravlev to obtain inflationary cosmological models without restrictions on a scalar field potential is employed here. We note that like scalar field, the inflationary solution obtained here with tachyon field also does not depend on its potential. However, unlike scalar field, inflation with tachyon is obtained for a restricted domains of the field to begin with. We obtain potentials for which one gets inflation using both scalar field and tachyon field separately. It is found that unlike the scalar field, the tachyonic field inflation sceanario can be realized from t > t_o.

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Research paper thumbnail of Observational constraints in the emergent universe model

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Research paper thumbnail of Lorentzian wormholes in an emergent universe

Classical and Quantum Gravity

A non-singular emergent universe (EU) scenario within the realm of standard Relativistic physics ... more A non-singular emergent universe (EU) scenario within the realm of standard Relativistic physics requires a generalization of the equation of state (EoS) connecting the pressure and energy density. This generalized EoS is capable of describing a composition of exotic matter, dark energy and cosmological dust matter. Since the EU scenario is known to violate the null energy condition (NEC), we investigate the possibility of presence of static, spherically symmetric and traversable Lorentzian wormholes in an EU. The obtained shape function is found to satisfy the criteria for wormhole formation, besides the violation of the NEC at the wormhole throat and ensuring traversability such that tidal forces are within desirable limits. Also, the wormhole is found to be stable through linear stability analysis. Most importantly, the numerical value of the EU parameter B as estimated by our wormhole model is in agreement with and lies within the range of values as constrained by observational ...

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Research paper thumbnail of Barrow Holographic Dark Energy in Brane World Cosmology

arXiv (Cornell University), Sep 13, 2022

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Research paper thumbnail of <i>NuSTAR</i> observation of X-ray pulsar 1E 1145.1−6141

Monthly Notices of the Royal Astronomical Society, Oct 10, 2022

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Research paper thumbnail of Accelerating universe in modified theories of gravity

Physical Review D, 2009

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Research paper thumbnail of Viscous cosmologies with variableΛin higher derivative gravity

Physical Review D, 2007

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Research paper thumbnail of Constraints on exotic matter needed for an emergent universe

Monthly Notices of the Royal Astronomical Society, 2010

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Research paper thumbnail of Revisiting SW J2000.6+3210: a persistent Be X-ray pulsar?

Monthly Notices of the Royal Astronomical Society, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Models of compact objects with charge in generalized Tolman-Kuchowicz metric

Astrophysics and Space Science

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Research paper thumbnail of NUSTAR and Swift observations of AMXP Swift J1756.9−2508 during its 2018 outburst

Monthly Notices of the Royal Astronomical Society, Oct 3, 2019

ABSTRACT We present here the timing and spectral analysis of the accreting millisecond pulsar (AM... more ABSTRACT We present here the timing and spectral analysis of the accreting millisecond pulsar (AMXP) SwiftJ1756.9−2508 during its recent outburst in 2018 using Swift and NUSTAR observations. The simultaneous fitting of the Swift and NUSTAR spectra indicates that the source was in the hard state with a cut-off energy of about 74.58 keV. We also study in detail the pulse profile of the AMXP and its dependence on energy. The colour–colour diagram of the source is different from those previously reported. We performed phase- and time-resolved spectral analysis using NUSTAR data. Pulse phase-resolved spectra were fitted with a power-law model and significant changes in the spectral parameters with pulse phase were observed. The orbital phase and time-resolved spectra were fitted with a cut-off power-law model. The column density and photon index obtained from orbital phase spectral analysis were found to show some anticorrelation with the flux. Through time-resolved spectral analysis, we observed that the spectral parameters show positive correlation with each other and with the flux. We do not observe a softening of the spectrum with time. No emission lines or Compton bump were observed in the spectrum of the AMXP.

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Research paper thumbnail of Modified Chaplygin gas and constraints on its<i>B</i>parameter from cold dark matter and unified dark matter energy cosmological models

Monthly Notices of the Royal Astronomical Society, Aug 21, 2009

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Research paper thumbnail of Nonsingular Black Holes in Higher dimensions

arXiv (Cornell University), 2023

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Research paper thumbnail of Inflation in Bianchi models and the cosmic no-hair theorem

Physical review, Nov 27, 2001

ABSTRACT

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Research paper thumbnail of Chaotic Inflationary Universe in Rastall Gravity

Canadian Journal of Physics, Jun 23, 2023

We study Linde’s chaotic inflation in Rastall gravity with a homogeneous scalar field. In Einstei... more We study Linde’s chaotic inflation in Rastall gravity with a homogeneous scalar field. In Einstein’s general theory of relativity, Linde obtained chaotic scenario, which emerged from chaotic distribution of scalar field satisfying a limiting value of the initial scalar field ϕo &gt; 3 MP that lies in the quantum gravity. The upper limit on the initial scalar field is obtained for a sufficient inflation to encompass the present universe. In the Rastall gravity, the upper limit is reduced depending on the Rastall parameter γ &lt; 1. The upper limit on ϕo is found to increases for [Formula: see text]. In the later case, sufficient inflation is not permitted and the role of curvaton field is explored for an acceptable early chaotic inflation.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Relativistic strange stars with anisotropy and B-parameter in pseudo spheroidal space time

Proceedings of the International Astronomical Union, Aug 1, 2012

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Power Law Inflation and the Cosmic No Hair Theorem in Brane World

Nucleation and Atmospheric Aerosols, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Observational constraints on modified Chaplygin gas in Horava–Lifshitz gravity with dark radiation

Pramana, Sep 28, 2013

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Can extended Chaplygin gas source a Hubble tension resolved emergent universe ?

arXiv (Cornell University), Jul 5, 2023

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An Introduction to Astronomical Data Analysis

The edited book contains seven chapters containing pedagogical approach of analysis of astronomic... more The edited book contains seven chapters containing pedagogical approach of analysis of astronomical and cosmological data. Cosmology is the study of the cosmos. Present decade is witnessing a transition of cosmology from a speculative science to an experimental science. A number of observational missions in the space in recent times lead to take up experiments and collect data that are pouring from last scattering surface of the sky in addition to stellar data. The advancement of science and technology made it possible to peep deep into the sky and consequently number of new phenomenon are captured by the detectors placed high up in the sky including terrestrial telescope. In this connection an introductory data analysis workshop organized at IUCAA Resource Centre, Physics Department, North Bengal University (NBU), India. It was felt that a write up will help the researchers for their data analysis with the observed data. Prof. D. Fraix-Burnet from France and other scientists from India discussed the method of data analysis and how to handle huge amount of data. This book is the outcome of the IUCAA sponsored workshop held at NBU.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Brane World Inflation with Scalar and Tachyon Fields

arXiv (Cornell University), Aug 7, 2007

We present inflationary models of the early universe in the braneworld scenario considering both ... more We present inflationary models of the early universe in the braneworld scenario considering both scalar field and tachyon field separately. The technique of Chervon and Zhuravlev to obtain inflationary cosmological models without restrictions on a scalar field potential is employed here. We note that like scalar field, the inflationary solution obtained here with tachyon field also does not depend on its potential. However, unlike scalar field, inflation with tachyon is obtained for a restricted domains of the field to begin with. We obtain potentials for which one gets inflation using both scalar field and tachyon field separately. It is found that unlike the scalar field, the tachyonic field inflation sceanario can be realized from t > t_o.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Observational constraints in the emergent universe model

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Lorentzian wormholes in an emergent universe

Classical and Quantum Gravity

A non-singular emergent universe (EU) scenario within the realm of standard Relativistic physics ... more A non-singular emergent universe (EU) scenario within the realm of standard Relativistic physics requires a generalization of the equation of state (EoS) connecting the pressure and energy density. This generalized EoS is capable of describing a composition of exotic matter, dark energy and cosmological dust matter. Since the EU scenario is known to violate the null energy condition (NEC), we investigate the possibility of presence of static, spherically symmetric and traversable Lorentzian wormholes in an EU. The obtained shape function is found to satisfy the criteria for wormhole formation, besides the violation of the NEC at the wormhole throat and ensuring traversability such that tidal forces are within desirable limits. Also, the wormhole is found to be stable through linear stability analysis. Most importantly, the numerical value of the EU parameter B as estimated by our wormhole model is in agreement with and lies within the range of values as constrained by observational ...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Barrow Holographic Dark Energy in Brane World Cosmology

arXiv (Cornell University), Sep 13, 2022

Bookmarks Related papers MentionsView impact

Research paper thumbnail of <i>NuSTAR</i> observation of X-ray pulsar 1E 1145.1−6141

Monthly Notices of the Royal Astronomical Society, Oct 10, 2022

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Accelerating universe in modified theories of gravity

Physical Review D, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Viscous cosmologies with variableΛin higher derivative gravity

Physical Review D, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Constraints on exotic matter needed for an emergent universe

Monthly Notices of the Royal Astronomical Society, 2010

Bookmarks Related papers MentionsView impact