2007PASP..119.1108Z

The possible detection of the fastest spinning nuclear-powered pulsar XTE J1739-285, of frequency 1122 Hz (0.8913 ms), arouses us to constrain the mass and radius of its central compact object and to infer the stellar matter composition: neutrons or quarks. Spun up by the accreting materials to such a high rotating speed, the compact star should have either a small radius or short innermost stable circular orbit. By the empirical relation between the upper kilohertz quasi-periodic oscillation frequency and star spin frequency, a strong constraint on mass and radius is obtained of 1.51 M_☉ and 10.9 km, respectively, which excludes most equations of state (EOSs) of normal neutrons and strongly hints the star promisingly to be a strange quark star. Furthermore, the star magnetic field is estimated to be about 4x10⁷ G<B<10⁹ G, which reconciles with those of millisecond radio pulsars, revealing the clues of the evolution linkage of two types of astrophysical objects.