X-ray pulsar radiation from polar cap heated by back-flow bombardment

We consider the problem of the thermal X-ray radiation from the hot polar cap of radio pulsars showing evidence of E×B subpulse drift in radio band. In our resent Paper I, within the partially screened gap (PSG) model of inner acceleration region we derived a simple relationship between the drift rate of subpulses observed in a radio-band and the thermal X-ray luminosity from polar caps heated by the back-flow particle bombardment. This relationship can be tested for pulsars in which the socalled carousel rotation time P4, reflecting the E×B plasma drift, and the thermal X-ray luminosity Lx from the hot polar cap are known. To test the model we used two only available pulsars: PSRs B0943+10 and B1133+16. They both satisfied the model prediction, although due to low photon statistics the thermal component could not be firmly identified from the X-ray data. Nevertheless, these pulsars were at least consistent with PSG pulsar model. In the present paper we consider two more pulsars: PSRs B0656+14 and B062828, whose data have been recently become available. In PSR B0656+14 the thermal radiation from the hot polar cap was clearly detected, as for PSR B0628-28, it also seems to be having such a component. It is important to note, that in all cases for which both P4 and Lx are presently known, the PSG pulsar model seems to be fully confirmed. Other available models of inner acceleration region fail to explain the observed relationship between radio and X-ray data. The pure vacuum gap model predicts too high Lx and too low P4, while the space charge limited model predicts too low Lx and the origin of the subpulse drift has no natural explanation.