Is PSR B0943+10 a Low-Mass Quark Star?

A recent X-ray observation has shown that the radio pulsar PSR B0943+10, withclear drifting subpulses, has a much smaller polar cap area than that ofconventional pulsars with mass of $\sim\msun$ and radius of $\sim10$ km. Zhanget al. (2005) addressed then that this new result conflicts with the standardvacuum gap model. Nonetheless, the discrepancy could be explained if PSRB0943+10 is actually a low-mass quark star. It is found that the potential dropin the open-field-line region of oblique pulsars (i.e., inclination angle$\alpha\neq 0$) might be $\sim 10^2$ times that of aligned pulsars, and thatPSR B0943+10 with $\alpha = 12.4^{\rm o}$ could be well above the deathline. Wethus conclude that the Ruderman-Sutherland-type vacuum gap model still workswell for this pulsar if it is a bare quark star with a mass of $\sim0.02M_\odot$ and a radius of $\sim 2.6$ km.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter