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Papers by BIKASH CHANDRA PAUL
Monthly Notices of the Royal Astronomical Society, 2013
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Astrophysics and Space Science
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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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Monthly Notices of the Royal Astronomical Society, Aug 21, 2009
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arXiv (Cornell University), 2023
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Physical review, Nov 27, 2001
ABSTRACT
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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 > 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 < 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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Proceedings of the International Astronomical Union, Aug 1, 2012
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Nucleation and Atmospheric Aerosols, 2006
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Pramana, Sep 28, 2013
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arXiv (Cornell University), Jul 5, 2023
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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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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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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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arXiv (Cornell University), Sep 13, 2022
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Monthly Notices of the Royal Astronomical Society, Oct 10, 2022
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Physical Review D, 2009
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Physical Review D, 2007
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Monthly Notices of the Royal Astronomical Society, 2010
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Monthly Notices of the Royal Astronomical Society, 2013
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Astrophysics and Space Science
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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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Monthly Notices of the Royal Astronomical Society, Aug 21, 2009
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arXiv (Cornell University), 2023
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Physical review, Nov 27, 2001
ABSTRACT
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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 > 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 < 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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Proceedings of the International Astronomical Union, Aug 1, 2012
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Nucleation and Atmospheric Aerosols, 2006
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Pramana, Sep 28, 2013
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arXiv (Cornell University), Jul 5, 2023
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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
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
Bookmarks Related papers MentionsView impact
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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arXiv (Cornell University), Sep 13, 2022
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Monthly Notices of the Royal Astronomical Society, Oct 10, 2022
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Physical Review D, 2009
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Physical Review D, 2007
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Monthly Notices of the Royal Astronomical Society, 2010
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