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Astron. Astrophys. 355, L19-L22 (2000)

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Letter to the Editor

Possible signatures for strange stars in stellar X-ray binaries

B. Datta;1;2  * , A.V. Thampan 3 and I. Bombaci 4

1 Indian Institute of Astrophysics, Bangalore 560 034, India
2 Raman Research Institute, Bangalore 560 080, India
3 Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune 411 007, India (arun@iucaa.ernet.in)
4 Dipartimento di Fisica Universitá di Pisa, and INFN Sezione di Pisa, via Buonarroti 2, 56127 Pisa, Italy (BOMBACI@pi.infn.it)

Received 9 December 1999 / Accepted 15 February 2000


Kilohertz quasi-periodic brightness oscillations (kHz QPOs) observed in certain X-ray burst sources may represent Keplerian frequencies in the inner regions of the accretion disk in such systems. If this assumption is strictly adhered to, we show here that if the central accretor in stellar X-ray burst sources is a strange star (made up of u, d and s quarks in beta equilibrium, referred to as strange matter) then the calculated QPO frequencies are reconcilable with the observed QPO frequencies (corresponding to the highest frequency of 1.22 kHz, observed so far from the source 4U 1636-53) only for particular values of the QCD-related parameters which describe the equation of state of strange matter. We demonstrate that QPO frequencies in the very high range (1.9-3.1) kHz can be understood in terms of a (non-magnetized) strange star X-ray binary (SSXB) rather than a neutron star X-ray binary (NSXB). Future discovery of such high frequency QPOs from X-ray burst sources will constitute a new astrophysical diagnostic for identifying solar mass range stable strange stars in our galaxy.

Key words: accretion, accretion disks – dense matter – equation of state – stars: binaries: close – stars: neutron – X-rays: bursts

* Deceased: December 3, 1999

Send offprint requests to: Arun V. Thampan

© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000