Manjari Bagchi | The Institute of Mathematical Sciences, Chennai (original) (raw)

Journal Papers by Manjari Bagchi

Research paper thumbnail of Constraining the luminosity function parameters and population size of radio pulsars in globular clusters

MNRAS, 2013

Studies of the Galactic population of radio pulsars have shown that their luminosity distribution... more Studies of the Galactic population of radio pulsars have shown that their luminosity distribution appears to be log-normal in form. We investigate some of the consequences that occur when one applies this functional form to populations of pulsars in globular clusters. We use Bayesian methods to explore constraints on the mean and standard deviation of the luminosity function, as well as the total number of pulsars, given an observed sample of pulsars down to some limiting flux density, accounting for measurements of flux densities of individual pulsars as well as diffuse emission from the direction of the cluster. We apply our analysis to Terzan 5, 47 Tucanae and M28, and demonstrate, under reasonable assumptions, that the number of potentially observable pulsars should be within 95 per cent credible intervals of 147 {^{+ 112}_{-65}} , 83 {^{+ 54}_{-35}} and 100 {^{+ 91}_{-52}} , respectively. Beaming considerations would increase the true population size by approximately a factor of 2. Using non-informative priors, however, the constraints are not tight due to the paucity and quality of flux density measurements. Future cluster pulsar discoveries and improved flux density measurements would allow this method to be used to more accurately constrain the luminosity function, and to compare the luminosity function between different clusters.

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Research paper thumbnail of Periastron advance in neutron star-black hole binaries

MNRAS, 2012

As neutron star-black hole binaries are expected to be discovered through future pulsar surveys u... more As neutron star-black hole binaries are expected to be discovered through future pulsar surveys using upcoming facilities, it is necessary to understand various observable properties of such systems. In this work, we study the advance of the periastron of such binaries under the post-Newtonian formalism over a wide range of parameters. We find that the first- and second-order post-Newtonian effects and the leading order spin-orbit coupling effects are significant for such binaries but higher order effects can be neglected.

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Research paper thumbnail of A search for dispersed radio bursts in archival Parkes Multibeam Pulsar Survey data

MNRAS, 2012

A number of different classes of potentially extra-terrestrial bursts of radio emission have been... more A number of different classes of potentially extra-terrestrial bursts of radio emission have been observed in surveys with the Parkes 64-m radio telescope, including 'rotating radio transients', the 'Lorimer burst' and 'perytons'. Rotating radio transients are radio pulsars which are best detectable in single-pulse searches. The Lorimer burst is a highly dispersed isolated radio burst with properties suggestive of extragalactic origin. Perytons share the frequency-swept nature of the rotating radio transients and Lorimer burst, but unlike these events appear in all 13 beams of the Parkes multibeam receiver and are probably a form of peculiar radio frequency interference. In order to constrain these and other radio source populations further, we searched the archival Parkes Multibeam Pulsar Survey data for events similar to any of these. We did not find any new rotating radio transients or bursts like the Lorimer burst. We did, however, discover four peryton-like events. Similar to the perytons, these four bursts are highly dispersed, detected in all 13 beams of the Parkes multibeam receiver, and have pulse widths between 20 and 30 ms. Unlike perytons, these bursts are not associated with atmospheric events like rain or lightning. These facts may indicate that lightning was not responsible for the peryton phenomenon. Moreover, the lack of highly dispersed celestial signals is the evidence that the Lorimer burst is unlikely to belong to a cosmological source population.

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Research paper thumbnail of Luminosities of recycled radio pulsars in globular clusters

MNRAS, 2011

Using Monte Carlo simulations, we model the luminosity distribution of recycled pulsars in globul... more Using Monte Carlo simulations, we model the luminosity distribution of recycled pulsars in globular clusters as the brighter, observable part of an intrinsic distribution. We find that the observed luminosities can be reproduced using either lognormal or power-law distributions as the underlying luminosity function. For both distributions, a wide range of model parameters provide an acceptable match to the observed sample, with the lognormal function providing statistically better agreement in general than the power-law models. Moreover, the power-law models predict a parent population size that is a factor of between 2 and 10 times higher than for the lognormal models. We note that the lognormal luminosity distribution found for the normal pulsar population by Faucher-Giguère and Kaspi is consistent with the observed luminosities of globular cluster pulsars. For Terzan 5, our simulations show that the sample of detectable radio pulsars, and the diffuse radio flux measurement, can be explained using the lognormal luminosity law with a parent population of ˜150 pulsars. Measurements of diffuse gamma-ray fluxes for several clusters can be explained by both power-law and lognormal models, with the lognormal distributions again providing a better match in general. In contrast to previous studies, we do not find any strong evidence for a correlation between the number of pulsars inferred in globular clusters and globular cluster parameters, including metallicity and stellar encounter rate.

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Research paper thumbnail of The role of binding energies of neutron stars on the accretion-driven evolution

MNRAS, 2011

Millisecond pulsars are believed to descend from low-mass X-ray binaries. Observable parameters o... more Millisecond pulsars are believed to descend from low-mass X-ray binaries. Observable parameters of binary millisecond pulsars, e.g. mass of the pulsar, mass of the companion, spin period of the pulsar, orbital period, orbital eccentricity, etc., are used to probe the past accretion history of the millisecond pulsars. However, unfortunately in these studies the binding energy of the neutron star is not commonly considered. We show that the effect of the binding energy is significant in the estimation of the amount of mass accretion, and thus should be incorporated in models for binary evolutions. Moreover, different equations of state for dense matter give different values for the accreted mass for the same amount of increase in the gravitational mass of the neutron star, implying the need of constraining dense matter equations of state even to understand the spin-up procedure properly.

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Research paper thumbnail of Luminosities of Radio Pulsars

IJMPD, 2013

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Research paper thumbnail of On the detectability of eccentric binary pulsars

MNRAS, 2013

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Research paper thumbnail of Goals, Strategies and First Discoveries of AO327, the Arecibo All-sky 327 MHz Drift Pulsar Survey

ApJ, 2013

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Research paper thumbnail of In what sense a neutron star-black hole binary is the holy grail for testing gravity?

JCAP, 2014

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Research paper thumbnail of Rotational parameters of strange stars in comparison with neutron stars

New Astronomy, 2010

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Research paper thumbnail of Orbital Eccentricity of Binary Radio Pulsars in Globular Clusters and the Interaction Between Stars

Astrophysical Journal, 2009

We analyze the observed distribution of the orbital eccentricity and period of binary radio pulsa... more We analyze the observed distribution of the orbital eccentricity and period of binary radio pulsars in globular clusters using computational tools to simulate binary-single star interactions. Globular clusters have different groups of pulsars arising from separate interaction scenarios. Intermediate eccentricities of cluster pulsars can be mostly accounted by fly-bys although locally lower stellar densities at pulsar positions may alter the situation. Very high eccentricities are likely to be results of exchanges and/or mergers of single stars with the binary companion of the pulsar.

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Research paper thumbnail of Ruling out Kozai resonance in highly eccentric galactic binary millisecond pulsar PSR J1903+0327

Monthly Notices of The Royal Astronomical Society, 2009

We investigate the observational signatures associated with one of the proposed formation scenari... more We investigate the observational signatures associated with one of the proposed formation scenario for the recently discovered highly eccentric binary millisecond pulsar (MSP) PSR J1903+0327 in the galactic plane. The scenario requires that the MSP to be part of a hierarchical triple (HT), consisting of inner and outer binaries, experiencing the Kozai resonance. Numerical modeling of a bound point mass HT, while incorporating the effects due to the quadrupolar interactions between the binary orbits and dominant contributions to the general relativistic periastron precession in the inner binary, reveals that, at the present epoch, the orbital eccentricity of the binary MSP should decrease for reasonable ranges in the HT parameters. The estimated decrements in the orbital eccentricity of the inner binary are few parts in 10510^{5}105, substantially higher than the reported accuracies in the estimation of the orbital eccentricity of the binary MSP, while employing various general relativistic timing models for isolated binary pulsars. For wide ranges in the allowed orbital parameters, the estimated rate of change in the eccentricity of the inner binary is orders of magnitude higher than the value recently measured by the pulsar timing analysis. Therefore, we rule out the scenario that the MSP is part of a HT undergoing the Kozai oscillations. The origin of this system in a typical globular cluster is also shown to be less likely than inferred in the discovery paper.

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Research paper thumbnail of Radio Pulsar Binaries in Globular Clusters: Their Orbital Eccentricities and Stellar Interactions

Astrophysical Journal, 2009

High sensitivity searches of globular clusters (GC) for radio pulsars by improved pulsar search a... more High sensitivity searches of globular clusters (GC) for radio pulsars by improved pulsar search algorithms and sustained pulsar timing observations have so far yielded some 140 pulsars in more than two dozen GCs. The observed distribution of orbital eccentricity and period of binary radio pulsars in GCs have imprints of the past interaction between single pulsars and binary systems or of binary pulsars and single passing non-compact stars. It is seen that GCs have different groups of pulsars. These may have arisen out of exchange or merger of a component of the binary with the incoming star or a "fly-by" in which the original binary remains intact but undergoes a change of eccentricity and orbital period. We consider the genesis of the distribution of pulsars using analytical and computational tools such as STARLAB, which performs numerical scattering experiments with direct N-body integration. Cluster pulsars with intermediate eccentricities can mostly be accounted for by fly-bys whereas those with high eccentricities are likely to be the result of exchanges and/or mergers of single stars with the binary companion of the pulsar, although there are a few objects which do not easily fit into this description. The corresponding distribution for galactic field pulsars shows notable differences from the GC pulsar orbital period and eccentricity distribution. The long orbital period pulsars in the galactic field with frozen out low eccentricities are largely missing from the globular clusters, and we show that ionization of these systems in GCs cannot alone account for the peculiarities.

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Research paper thumbnail of Newtonian and general relativistic contribution of gravity to surface tension of strange stars

Astronomy & Astrophysics, 2005

Surface tension (S) is due to the inward force experienced by particles at the surface and usuall... more Surface tension (S) is due to the inward force experienced by particles at the surface and usually gravitation does not play an important role in this force. But in compact stars the gravitational force on the particles is very large and S is found to depend not only on the interactions in the strange quark matter, but also on the structure of the star, i.e. on its mass and radius. Indeed, it has been claimed recently that 511 keV photons observed by the space probe INTEGRAL from the galactic bulge may be due to electron-positron annihilation, and their source may be the positron cloud outside of an antiquark star. Such stars, if they exist, may also go a long way towards explaining away the antibaryon deficit of the universe. For that to happen S must be high enough to allow for survival of quark/antiquark stars born in early stages of the formation of the universe. High value of S may also assist explanation of delayed gamma-ray burst after a supernova explosion, as conversion from normal matter to strange matter takes place. The possibility of some implications from formation of surface waves are also discussed.

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Research paper thumbnail of Bound for entropy and viscosity ratio of strange quark matter

Physics Letters B, 2008

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Research paper thumbnail of High-Density Skyrmion Matter and Neutron Stars

Astrophysical Journal, 2008

We examine neutron star properties based on a model of dense matter composed of B=1 skyrmions imm... more We examine neutron star properties based on a model of dense matter composed of B=1 skyrmions immersed in a mesonic mean field background. The model realizes spontaneous chiral symmetry breaking non-linearly and incorporates scale-breaking of QCD through a dilaton VEV that also affects the mean fields. Quartic self-interactions among the vector mesons are introduced on grounds of naturalness in the corresponding effective field theory. Within a plausible range of the quartic couplings, the model generates neutron star masses and radii that are consistent with a preponderance of observational constraints, including recent ones that point to the existence of relatively massive neutron stars with mass M 1.7 Msun and radius R (12-14) km. If the existence of neutron stars with such dimensions is confirmed, matter at supra-nuclear density is stiffer than extrapolations of most microscopic models suggest.

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Research paper thumbnail of Members of the double pulsar system PSR J0737-3039: Neutron stars or strange stars

New Astronomy, 2009

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Research paper thumbnail of Incompressibility of strange matter

Physics Letters B, 2004

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Research paper thumbnail of Strange pulsar hypothesis

Monthly Notices of The Royal Astronomical Society, 2006

It appears that there is a genuine shortage of radio pulsars with surface magnetic fields signifi... more It appears that there is a genuine shortage of radio pulsars with surface magnetic fields significantly smaller than sim108\sim 10^8sim108 Gauss. We propose that the pulsars with very low magnetic fields are actually strange stars locked in a state of minimum free energy and therefore at a limiting value of the magnetic field which can not be lowered by the system spontaneously.

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Research paper thumbnail of A Three-Stage Model for the Inner Engine of Gamma-Ray Bursts: Prompt Emission and Early Afterglow

Astrophysical Journal, 2007

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Research paper thumbnail of Constraining the luminosity function parameters and population size of radio pulsars in globular clusters

MNRAS, 2013

Studies of the Galactic population of radio pulsars have shown that their luminosity distribution... more Studies of the Galactic population of radio pulsars have shown that their luminosity distribution appears to be log-normal in form. We investigate some of the consequences that occur when one applies this functional form to populations of pulsars in globular clusters. We use Bayesian methods to explore constraints on the mean and standard deviation of the luminosity function, as well as the total number of pulsars, given an observed sample of pulsars down to some limiting flux density, accounting for measurements of flux densities of individual pulsars as well as diffuse emission from the direction of the cluster. We apply our analysis to Terzan 5, 47 Tucanae and M28, and demonstrate, under reasonable assumptions, that the number of potentially observable pulsars should be within 95 per cent credible intervals of 147 {^{+ 112}_{-65}} , 83 {^{+ 54}_{-35}} and 100 {^{+ 91}_{-52}} , respectively. Beaming considerations would increase the true population size by approximately a factor of 2. Using non-informative priors, however, the constraints are not tight due to the paucity and quality of flux density measurements. Future cluster pulsar discoveries and improved flux density measurements would allow this method to be used to more accurately constrain the luminosity function, and to compare the luminosity function between different clusters.

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Research paper thumbnail of Periastron advance in neutron star-black hole binaries

MNRAS, 2012

As neutron star-black hole binaries are expected to be discovered through future pulsar surveys u... more As neutron star-black hole binaries are expected to be discovered through future pulsar surveys using upcoming facilities, it is necessary to understand various observable properties of such systems. In this work, we study the advance of the periastron of such binaries under the post-Newtonian formalism over a wide range of parameters. We find that the first- and second-order post-Newtonian effects and the leading order spin-orbit coupling effects are significant for such binaries but higher order effects can be neglected.

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Research paper thumbnail of A search for dispersed radio bursts in archival Parkes Multibeam Pulsar Survey data

MNRAS, 2012

A number of different classes of potentially extra-terrestrial bursts of radio emission have been... more A number of different classes of potentially extra-terrestrial bursts of radio emission have been observed in surveys with the Parkes 64-m radio telescope, including 'rotating radio transients', the 'Lorimer burst' and 'perytons'. Rotating radio transients are radio pulsars which are best detectable in single-pulse searches. The Lorimer burst is a highly dispersed isolated radio burst with properties suggestive of extragalactic origin. Perytons share the frequency-swept nature of the rotating radio transients and Lorimer burst, but unlike these events appear in all 13 beams of the Parkes multibeam receiver and are probably a form of peculiar radio frequency interference. In order to constrain these and other radio source populations further, we searched the archival Parkes Multibeam Pulsar Survey data for events similar to any of these. We did not find any new rotating radio transients or bursts like the Lorimer burst. We did, however, discover four peryton-like events. Similar to the perytons, these four bursts are highly dispersed, detected in all 13 beams of the Parkes multibeam receiver, and have pulse widths between 20 and 30 ms. Unlike perytons, these bursts are not associated with atmospheric events like rain or lightning. These facts may indicate that lightning was not responsible for the peryton phenomenon. Moreover, the lack of highly dispersed celestial signals is the evidence that the Lorimer burst is unlikely to belong to a cosmological source population.

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Research paper thumbnail of Luminosities of recycled radio pulsars in globular clusters

MNRAS, 2011

Using Monte Carlo simulations, we model the luminosity distribution of recycled pulsars in globul... more Using Monte Carlo simulations, we model the luminosity distribution of recycled pulsars in globular clusters as the brighter, observable part of an intrinsic distribution. We find that the observed luminosities can be reproduced using either lognormal or power-law distributions as the underlying luminosity function. For both distributions, a wide range of model parameters provide an acceptable match to the observed sample, with the lognormal function providing statistically better agreement in general than the power-law models. Moreover, the power-law models predict a parent population size that is a factor of between 2 and 10 times higher than for the lognormal models. We note that the lognormal luminosity distribution found for the normal pulsar population by Faucher-Giguère and Kaspi is consistent with the observed luminosities of globular cluster pulsars. For Terzan 5, our simulations show that the sample of detectable radio pulsars, and the diffuse radio flux measurement, can be explained using the lognormal luminosity law with a parent population of ˜150 pulsars. Measurements of diffuse gamma-ray fluxes for several clusters can be explained by both power-law and lognormal models, with the lognormal distributions again providing a better match in general. In contrast to previous studies, we do not find any strong evidence for a correlation between the number of pulsars inferred in globular clusters and globular cluster parameters, including metallicity and stellar encounter rate.

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Research paper thumbnail of The role of binding energies of neutron stars on the accretion-driven evolution

MNRAS, 2011

Millisecond pulsars are believed to descend from low-mass X-ray binaries. Observable parameters o... more Millisecond pulsars are believed to descend from low-mass X-ray binaries. Observable parameters of binary millisecond pulsars, e.g. mass of the pulsar, mass of the companion, spin period of the pulsar, orbital period, orbital eccentricity, etc., are used to probe the past accretion history of the millisecond pulsars. However, unfortunately in these studies the binding energy of the neutron star is not commonly considered. We show that the effect of the binding energy is significant in the estimation of the amount of mass accretion, and thus should be incorporated in models for binary evolutions. Moreover, different equations of state for dense matter give different values for the accreted mass for the same amount of increase in the gravitational mass of the neutron star, implying the need of constraining dense matter equations of state even to understand the spin-up procedure properly.

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Research paper thumbnail of Luminosities of Radio Pulsars

IJMPD, 2013

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Research paper thumbnail of On the detectability of eccentric binary pulsars

MNRAS, 2013

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Research paper thumbnail of Goals, Strategies and First Discoveries of AO327, the Arecibo All-sky 327 MHz Drift Pulsar Survey

ApJ, 2013

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Research paper thumbnail of In what sense a neutron star-black hole binary is the holy grail for testing gravity?

JCAP, 2014

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Research paper thumbnail of Rotational parameters of strange stars in comparison with neutron stars

New Astronomy, 2010

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Research paper thumbnail of Orbital Eccentricity of Binary Radio Pulsars in Globular Clusters and the Interaction Between Stars

Astrophysical Journal, 2009

We analyze the observed distribution of the orbital eccentricity and period of binary radio pulsa... more We analyze the observed distribution of the orbital eccentricity and period of binary radio pulsars in globular clusters using computational tools to simulate binary-single star interactions. Globular clusters have different groups of pulsars arising from separate interaction scenarios. Intermediate eccentricities of cluster pulsars can be mostly accounted by fly-bys although locally lower stellar densities at pulsar positions may alter the situation. Very high eccentricities are likely to be results of exchanges and/or mergers of single stars with the binary companion of the pulsar.

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Research paper thumbnail of Ruling out Kozai resonance in highly eccentric galactic binary millisecond pulsar PSR J1903+0327

Monthly Notices of The Royal Astronomical Society, 2009

We investigate the observational signatures associated with one of the proposed formation scenari... more We investigate the observational signatures associated with one of the proposed formation scenario for the recently discovered highly eccentric binary millisecond pulsar (MSP) PSR J1903+0327 in the galactic plane. The scenario requires that the MSP to be part of a hierarchical triple (HT), consisting of inner and outer binaries, experiencing the Kozai resonance. Numerical modeling of a bound point mass HT, while incorporating the effects due to the quadrupolar interactions between the binary orbits and dominant contributions to the general relativistic periastron precession in the inner binary, reveals that, at the present epoch, the orbital eccentricity of the binary MSP should decrease for reasonable ranges in the HT parameters. The estimated decrements in the orbital eccentricity of the inner binary are few parts in 10510^{5}105, substantially higher than the reported accuracies in the estimation of the orbital eccentricity of the binary MSP, while employing various general relativistic timing models for isolated binary pulsars. For wide ranges in the allowed orbital parameters, the estimated rate of change in the eccentricity of the inner binary is orders of magnitude higher than the value recently measured by the pulsar timing analysis. Therefore, we rule out the scenario that the MSP is part of a HT undergoing the Kozai oscillations. The origin of this system in a typical globular cluster is also shown to be less likely than inferred in the discovery paper.

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Research paper thumbnail of Radio Pulsar Binaries in Globular Clusters: Their Orbital Eccentricities and Stellar Interactions

Astrophysical Journal, 2009

High sensitivity searches of globular clusters (GC) for radio pulsars by improved pulsar search a... more High sensitivity searches of globular clusters (GC) for radio pulsars by improved pulsar search algorithms and sustained pulsar timing observations have so far yielded some 140 pulsars in more than two dozen GCs. The observed distribution of orbital eccentricity and period of binary radio pulsars in GCs have imprints of the past interaction between single pulsars and binary systems or of binary pulsars and single passing non-compact stars. It is seen that GCs have different groups of pulsars. These may have arisen out of exchange or merger of a component of the binary with the incoming star or a "fly-by" in which the original binary remains intact but undergoes a change of eccentricity and orbital period. We consider the genesis of the distribution of pulsars using analytical and computational tools such as STARLAB, which performs numerical scattering experiments with direct N-body integration. Cluster pulsars with intermediate eccentricities can mostly be accounted for by fly-bys whereas those with high eccentricities are likely to be the result of exchanges and/or mergers of single stars with the binary companion of the pulsar, although there are a few objects which do not easily fit into this description. The corresponding distribution for galactic field pulsars shows notable differences from the GC pulsar orbital period and eccentricity distribution. The long orbital period pulsars in the galactic field with frozen out low eccentricities are largely missing from the globular clusters, and we show that ionization of these systems in GCs cannot alone account for the peculiarities.

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Research paper thumbnail of Newtonian and general relativistic contribution of gravity to surface tension of strange stars

Astronomy & Astrophysics, 2005

Surface tension (S) is due to the inward force experienced by particles at the surface and usuall... more Surface tension (S) is due to the inward force experienced by particles at the surface and usually gravitation does not play an important role in this force. But in compact stars the gravitational force on the particles is very large and S is found to depend not only on the interactions in the strange quark matter, but also on the structure of the star, i.e. on its mass and radius. Indeed, it has been claimed recently that 511 keV photons observed by the space probe INTEGRAL from the galactic bulge may be due to electron-positron annihilation, and their source may be the positron cloud outside of an antiquark star. Such stars, if they exist, may also go a long way towards explaining away the antibaryon deficit of the universe. For that to happen S must be high enough to allow for survival of quark/antiquark stars born in early stages of the formation of the universe. High value of S may also assist explanation of delayed gamma-ray burst after a supernova explosion, as conversion from normal matter to strange matter takes place. The possibility of some implications from formation of surface waves are also discussed.

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Research paper thumbnail of Bound for entropy and viscosity ratio of strange quark matter

Physics Letters B, 2008

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Research paper thumbnail of High-Density Skyrmion Matter and Neutron Stars

Astrophysical Journal, 2008

We examine neutron star properties based on a model of dense matter composed of B=1 skyrmions imm... more We examine neutron star properties based on a model of dense matter composed of B=1 skyrmions immersed in a mesonic mean field background. The model realizes spontaneous chiral symmetry breaking non-linearly and incorporates scale-breaking of QCD through a dilaton VEV that also affects the mean fields. Quartic self-interactions among the vector mesons are introduced on grounds of naturalness in the corresponding effective field theory. Within a plausible range of the quartic couplings, the model generates neutron star masses and radii that are consistent with a preponderance of observational constraints, including recent ones that point to the existence of relatively massive neutron stars with mass M 1.7 Msun and radius R (12-14) km. If the existence of neutron stars with such dimensions is confirmed, matter at supra-nuclear density is stiffer than extrapolations of most microscopic models suggest.

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Research paper thumbnail of Members of the double pulsar system PSR J0737-3039: Neutron stars or strange stars

New Astronomy, 2009

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Research paper thumbnail of Incompressibility of strange matter

Physics Letters B, 2004

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Research paper thumbnail of Strange pulsar hypothesis

Monthly Notices of The Royal Astronomical Society, 2006

It appears that there is a genuine shortage of radio pulsars with surface magnetic fields signifi... more It appears that there is a genuine shortage of radio pulsars with surface magnetic fields significantly smaller than sim108\sim 10^8sim108 Gauss. We propose that the pulsars with very low magnetic fields are actually strange stars locked in a state of minimum free energy and therefore at a limiting value of the magnetic field which can not be lowered by the system spontaneously.

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Research paper thumbnail of A Three-Stage Model for the Inner Engine of Gamma-Ray Bursts: Prompt Emission and Early Afterglow

Astrophysical Journal, 2007

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Research paper thumbnail of The luminosity function of cluster pulsars

We study luminosities of millisecond pulsars in globular clusters by fitting the observed luminos... more We study luminosities of millisecond pulsars in globular clusters by fitting the observed luminosity distribution with single and double power laws. We use simulations to model the observed distribution as the brighter part of some parent distribution for Terzan 5 and try to find a model which simultaneously agrees with the observed diffuse radio flux, total predicted number of pulsars and observed luminosity distribution. We find that wide ranges of parameters for log-normal and power-law distributions give such good models. No clear difference between the luminosity distributions of millisecond pulsars in globular clusters and normal disk pulsars was seen.

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Research paper thumbnail of Constraining the luminosity function parameters and population size of radio pulsars in globular clusters

The luminosity distribution of Galactic radio pulsars is believed to be log-normal in form. Apply... more The luminosity distribution of Galactic radio pulsars is believed to be log-normal in form. Applying this functional form to populations of pulsars in globular clusters, we employ Bayesian methods to explore constraints on the mean and standard deviation of the function, as well as the total number of pulsars in the cluster. Our analysis is based on an observed number of pulsars down to some limiting flux density, measurements of flux densities of individual pulsars, as well as diffuse emission from the direction of the cluster. We apply our analysis to Terzan 5 and demonstrate, under reasonable assumptions, that the number of potentially observable pulsars is in a 95.45% credible interval of 133+101 -58. Beaming considerations would increase the true population size by approximately a factor of two.

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Research paper thumbnail of Orbital Parameters of Binary Radio Pulsars in Globular Clusters and Stellar Interactions

The observed distribution of globular cluster binary radio pulsars in the eccentricity versus orb... more The observed distribution of globular cluster binary radio pulsars in the eccentricity versus orbital period plane can be explained as a result of binary-single star interactions. Our numerical and analytical study hints that the highest eccentricity binaries in clusters are likely to be from exchange and/or merger of a single star with a binary component, while the intermediate eccentricity systems are probably results of fly-by interactions.

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Research paper thumbnail of Strange Stars : An interesting member of the compact object family

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Research paper thumbnail of Strange star Equation of State with a modified Richardson potential

Advances in Space Research, 2006

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Research paper thumbnail of Strange stars at finite temperature

Journal of Physics: Conference Series, 2006

We calculate strange star properties, using large N_c approximation with built-in chiral symmetry... more We calculate strange star properties, using large N_c approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock mean field approximation method, using a modified Richardson potential with two scale parameters \Lambda and \Lambda^\prime, to find a new set of equation of states for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom and CSM.

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Research paper thumbnail of The detectability of eccentric binary pulsars

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Research paper thumbnail of Addendum to ``Decoupling of pion coupling <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msub><mi>f</mi><mi>π</mi></msub></mrow><annotation encoding="application/x-tex">f_{\pi}</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.1514em;"><span style="top:-2.55em;margin-left:-0.1076em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight"><span class="mord mathnormal mtight" style="margin-right:0.03588em;">π</span></span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span></span></span></span> from quarks at high density in three models, and its possible observational consequences

The pions decouple from quarks while their coupling to nucleons gpiNNg_{\pi NN}gpiNN remains unchanged at... more The pions decouple from quarks while their coupling to nucleons gpiNNg_{\pi NN}gpiNN remains unchanged at high density. This will have consequences for some recent papers.

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Research paper thumbnail of Orbital Parameters of Binary Radio Pulsars : Revealing Their Structure, Formation, Evolution and Dynamic History

Orbital parameters of binary radio pulsars reveal the history of the pulsars' formation and evolu... more Orbital parameters of binary radio pulsars reveal the history of the pulsars' formation and evolution including dynamic interactions with other objects. Advanced technology has enabled us to determine these orbital parameters accurately in most of the cases. Determination of post-Keplerian parameters of double neutron star binaries (especially of the double pulsar) provide clean tests of GTR and in the future may lead us to constrain the dense matter EoS. For binary pulsars with MS or WD companions, knowledge about the values of the orbital parameters as well as of the spin periods and the masses of the pulsars and the companions might be useful to understand the evolutionary history of the systems. As accreting neutron star binaries lead to orbit circularization due to the tidal coupling during accretion, their descendants i.e. binary MSPs are expected to be in circular orbits. On the other hand, dense stellar environments inside globular clusters (GCs) cause different types of interactions of single stars with pulsar binaries. These interactions can impart high eccentricities to the pulsar binaries. So it is quite common to get eccentric millisecond pulsar binaries in GCs and we find that "fly-by" causes intermediate values of eccentricities while "exchange" or "merger" causes high values of eccentricities. We also show that "ionization" is not much effective in the present stage of GCs. Even in the absence of such kinds of stellar interactions, a millisecond pulsar can have an eccentric orbit as a result of Kozai resonance if the pulsar binary is a member of a hierarchical triple system. PSR J1903+0327 is the only one eccentric millisecond pulsar binary in the galactic disk where stellar interactions are negligible. The possibility of this system to be a member of a hierarchical triple system or past association of a GC have been studied and found to be less likely.

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Research paper thumbnail of On the detectability of eccentric binary pulsars

By generalizing earlier work of Johnston & Kulkarni, we present a detailed description of the red... more By generalizing earlier work of Johnston & Kulkarni, we present a detailed description of the reduction in the signal-to-noise ratio for observations of binary pulsars. We present analytical expressions, and provide software, to calculate the sensitivity reduction for orbits of arbitrary eccentricity. We find that this reduction can be quite significant, especially in the case of a massive companion like another neutron star or a black hole. On the other hand, the reduction is less for highly eccentric orbits. We also demonstrate that this loss of sensitivity can be recovered by employing "acceleration search" or "acceleration-jerk search" algorithms.

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Research paper thumbnail of Population Synthesis of Double Neutron Stars

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Research paper thumbnail of Explanation of GRB and Early Afterglows as Quark-Nova Phenomenon

The recent studies of early afterglows of Gamma-Ray Bursts (GRB) with Swiftsatellite reveals some... more The recent studies of early afterglows of Gamma-Ray Bursts (GRB) with Swiftsatellite reveals some interesting phenomena which we are modelling with Quark-Nova. This involves strange stars which operate in two steps. Instep one, normal nuclear matter gets converted to strange quark matter dueto the extreme physical conditions created by a supernova. This strangequark matter then shrinks to form a strange

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Research paper thumbnail of Binary radio pulsars in globular clusters: their interaction with other stars and orbital eccentricities

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Research paper thumbnail of Skyrmion Stars

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Research paper thumbnail of BINARY PULSARS IN GCs

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Research paper thumbnail of Magnetic moments of baryons from a large N_c Fock calculation

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Research paper thumbnail of Magnetic moments of baryons µB from Fock calculations comparing Franklin’s and other sumrules for µB-s

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Research paper thumbnail of Population synthesis of double neutron stars

Monthly Notices of the Royal Astronomical Society, 2011

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Research paper thumbnail of Importance of constraining the dense matter Equation of State in pulsar astrophysics

Arxiv preprint arXiv:0709.0227, 2007

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Research paper thumbnail of Explanation of GRB and Early Afterglows as Quark-Nova Phenomenon

The recent studies of early afterglows of Gamma-Ray Bursts (GRB) with Swiftsatellite reveals some... more The recent studies of early afterglows of Gamma-Ray Bursts (GRB) with Swiftsatellite reveals some interesting phenomena which we are modelling with Quark-Nova. This involves strange stars which operate in two steps. Instep one, normal nuclear matter gets converted to strange quark matter dueto the extreme physical conditions created by a supernova. This strangequark matter then shrinks to form a strange

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Research paper thumbnail of Chromo-thermal instabilities and collapse of quark stars to black holes Astrophysical Implications

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Research paper thumbnail of Double neutron stars as double strange stars

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Research paper thumbnail of Observed Supersymmetry and Parity Doubling of Excited Hadrons

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Research paper thumbnail of Entropy & viscosity bound of strange stars

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