Narrow Results

The properties of rotating quark star are studied using the equation of state obtained from chiral colour dielectric model. The results are compared with those obtained from MIT bag model equation of state. The frequencies in the corotating innermost circular orbits for different central densities are evaluated and compared with the observed data.

We give a brief review on the neutron star spin frequency and its relation to the kHz QPOs. A simple power law relation can be applicable for the Atoll and Z sources with the slightly different power index, e.g. ν1 ~ 700(Hz)(ν2/1000)^1.8; However, for the two accretion induced millisecond X-ray pulsars, Sax J 1808.4-3658 and XTE 1807-294, their low values of twin kHz QPO separations make them different from the other QPO sources. In addition, there are not found the clear relation between a spin frequency and the twin kHz QPO separation, which seems to hint that the beat model for kHz QPOs confronts the difficulty. The kHz QPO separations are not constant, varied up and down with accretion rate, so the models that follow this tendency are the relativistic precession model by Stella & Vietri and the Alfvën wave oscillation model by Zhang. Averagely, the ratio of upper kHz QPO frequency to the lower one is very close to 1.5, then for Cir X-1 this ratio (~ 3) is unusual higher than those of the other sources.

When a magnetized accretion disk approach its last stable orbit, the relativistic effects result in another flavor of the AEI, the Relativistic AEI. Here we will focus on the consequences on the LFQPO and how this can be used to explain the less frequent B- and A-types of LFQPO.