2001 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/628

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Subject: search.filters.subject.Stars: neutron

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    Temperature profiles of accretion discs around rapidly rotating strange stars in general relativity : a comparison with neutron stars
    (2001-07-05) Bhattacharyya, Sudip; Thampan, A. V.; Bombaci, Ignazio
    We compute the temperature pro les of accretion discs around rapidly rotating strange stars, using constant gravitational mass equilibrium sequences of these objects, considering the full e ect of general relativity. Beyond a certain critical value of stellar angular momentum (J), we observe the radius (rorb) of the innermost stable circular orbit (ISCO) to increase with J (a property seen neither in rotating black holes nor in rotating neutron stars). The reason for this is traced to the crucial dependence of drorb=dJ on the rate of change of the radial gradient of the Keplerian angular velocity at rorb with respect to J. The structure parameters and temperature pro les obtained are compared with those of neutron stars, as an attempt to provide signatures for distinguishing between the two. We show that when the full gamut of strange star equation of state models, with varying degrees of sti ness are considered, there exists a substantial overlap in properties of both neutron stars and strange stars. However, applying accretion disc model constraints to rule out sti strange star equation of state models, we notice that neutron stars and strange stars exclusively occupy certain parameter spaces. This result implies the possibility of distinguishing these objects from each other by sensitive observations through future X{ray detectors.
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    Torque decay in the pulsar (p,p) diagrom effects of crustal ohmic dissipation and alignment
    (2001-07-05) Tauris, T. M.; Konar, Sushan
    We investigate the evolution of pulsars in the (P, ˙ P) diagram. We first present analytical formulae to follow the evolution of a pulsar using simple exponential models for magnetic field decay and alignment. We then compare these evolutionary tracks with detailed model calculations using ohmic decay of crustal neutron star magnetic fields. We find that, after an initial phase with a small braking index, n, pulsars evolve with enhanced torque decay (n ≫ 3) for about 1 Myr. The long term evolution depends on the impurity parameter of the crust. If impurities are negligible in older isolated pulsars we expect their true age to be approximately equal to their observed characteristic age, τ = P/(2 ˙ P). It is not possible from data to constrain model parameters of the neutron star crust.