An XMM-Newton observation of the drifting pulsar B0943+10

Radio pulsar subpulse drifting has been interpreted as rotation of subbeams (sparks) of pair plasma produced by intermittent breakdowns of an inner vacuum gap above the pulsar polar cap. This model also predicts strong thermal X-ray emission from the polar cap caused by inflowing particles created in spark discharges. We have observed the best-studied drifting pulsar B0943+10 with XMM-Newton and detected a point source coincident with the radio pulsar position. Its spectrum could be fitted with a thermal blackbody model, although a power-law model is also acceptable. The thermal fit gives a bolometric luminosity L_bol ≈ 5 × 10₂₈ ergs s^-1 and a surface area A ≈ 10₃(T/3 MK)^-4 m², much smaller than the conventional polar cap area, 6 × 10⁴ m². Such thermal radiation can be interpreted as emitted from footprints of sparks drifting in an inner gap of a height h ∼ (0. 1-0.2)r_pc, where r_pc is the polar cap radius. However, the original vacuum gap model by Ruderman & Sutherland requires some modification to reconcile the X-ray and radio data.