Browsing by Author "Thampan, A. V."

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Luminosities of Disk-Accreting non-magnetic neutron stars
(2001-03-02) Thampan, A. V.
Disk accretion onto a neutron star possessing a weak surface magnetic ﬁeld (B ≤ 108 G) provides interesting X-ray emission scenarios, and is relevant for understanding X-ray bursters and low-mass X-ray binaries (LMXBs). The stan- dard (Newtonian) theory of disk-accretion predicts that the matter spiralling in from inﬁnity loses one-half of its total gravitational energy in the extended disk, and the remainder in a narrow boundary layer girdling the neutron star. The ratio of the boundary layer luminosity to that from the disk (EBL/ED) is, there- fore, unity. On incorporation of general relativity without rotation (Schwarzschild solution), EBL/ED is seen to be as high as 6. We construct rotating sequences of neutron stars for three representative equations of state. We show here that for a neutron star rotating at a limit where centrifugal force balances the inward gravitational force, EBL/ED ∼ 0
Rapidly rotating strange stars for a new equation of state of strange quark matter
(2000-12-18) Bombaci, Ignazio; Thampan, A. V.; Datta, Bhaskar
For a new equation of state of strange quark matter, we construct equilibrium sequences of rapidly rotating strange stars in general relativity. The sequences are the normal and supramassive evolutionary sequences of constant rest mass. We also calculate equilibrium sequences for a constant value of Ω corresponding to the most rapidly rotating pulsar PSR 1937 +21. In addition to this, we calculate the radius of the marginally stable orbit and its dependence on Ω, relevant for modeling of kilo–Hertz quasi–periodic oscillations in X–ray binaries.
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.