78 research outputs found
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 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.Comment: Invited chapter in "Pulsars: Theory, Categories and Applications",
Editor: Alexander D. Morozov, 2010, Nova Science Publishers, ISBN:
978-1-61668-919-3; Typos correcte
Prospects of constraining the dense matter equation of state from the timing analysis of pulsars in double neutron star binaries: the cases of PSR J0737-3039A and PSR J1757-1854
The Lense-Thirring effect from spinning neutron stars in double neutron star
binaries contribute to the periastron advance of the orbit. This extra term
involves the moment of inertia of the neutron stars. Moment of inertia, on the
other hand, depends on the mass and spin of the neutron star as well as the
equation of state of the matter. If at least one member of the double neutron
star binary (better the faster one) is a radio pulsar, then accurate timing
analysis might lead to the estimation of the contribution of the Lense-Thirring
effect to the periastron advance, which will lead to the measurement of the
moment of inertia of the pulsar. Combination of the knowledge on the values of
the moment of inertia, the mass, and the spin of the pulsar, will give a new
constraint on the equation of state. Pulsars in double neutron star binaries
are the best for this purpose as short orbits and moderately high
eccentricities make the Lense-Thirring effect substantial, whereas tidal
effects are negligible (unlike pulsars with main sequence or white-dwarf
binaries). The most promising pulsars are PSR J0737-3039A and PSR J1757-1854.
The spin-precession of pulsars due to the misalignment between the spin and the
orbital angular momentum vectors affect the contribution of the Lense-Thirring
effect to the periastron advance. This effect has been explored for both PSR
J0737-3039A and PSR J1757-1854, and as the misalignment angles for both of
these pulsars are small, the variation in the Lense-Thirring term is not much.
However, to extract the Lense-Thirring effect from the observed rate of the
periastron advance, more accurate timing solutions including precise proper
motion and distance measurements are essential.Comment: To appear in the special issue of `Universe' dedicated to the
conference: "Compact Stars in the QCD Phase Diagram VI" held at The Joint
Institute for Nuclear Research (JINR), Dubna, Russia; during 26 - 29
September, 201
The role of binding energies of neutron stars on the accretion driven evolution
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. But unfortunately in these studies, binding energy of the
neutron star is not considered commonly. 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.Comment: Accepted for publication in MNRAS Letter
Periastron advance in neutron star–black hole binaries
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 the present 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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