Is PSR B0943+10 a low-mass quark star?

A recent X-ray observation has shown that the radio pulsar PSR B0943+10, with clear drifting subpulses, has a much smaller polar cap area than that of conventional pulsars with mass of $\sim\msun$ and radius of $\sim10$ km. Zhang et al. (2005) addressed then that this new result conflicts with the standard vacuum gap model. Nonetheless, the discrepancy could be explained if PSR B0943+10 is actually a low-mass quark star. It is found that the potential drop in 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 that PSR B0943+10 with $\alpha = 12.4^{\rm o}$ could be well above the deathline. We thus conclude that the Ruderman-Sutherland-type vacuum gap model still works well for this pulsar if it is a bare quark star with a mass of $\sim 0.02M_\odot$ and a radius of $\sim 2.6$ km.