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kHz QPOs in LMXBs, relations between different frequencies and compactness of stars |
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| Authors: | Taparati GangopadhyayXiang-Dong Li Subharthi RayMira Dey Jishnu Dey |
| Institution: | a Department of Physics, Presidency University, Kolkata 700 073, India b Department of Astronomy and Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210093, PR China c Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Durban 4000, South Africa |
| Abstract: | We suggest that the mass of four compact stars SAX J1808.4-3658, KS 1731-260, SAX J1750.8-2900 and IGR J17191-2821 can be determined from the difference in the observed kiloHertz quasi periodic oscillations (kHz QPO-s) of these stars. The stellar radius is very close to the marginally stable orbit Rms as predicted by Einstein’s general relativity. It may be noted that the first of these stars was suggested to be a strange star more than a decade back by Li et al. (1999a) from the unique millisecond X-ray pulsations with an accurate determination of its rotation period. It showed kHz QPO-s eight years back and so far it is the only set that has been observed. This is the first time we give an estimate of the mass of the star and of three other compact stars in low-mass X-ray binaries using their observed kHz QPO-s. |
| Keywords: | kHz QPOs Strange stars |
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