2007MNRAS.376L..67G

We consider the problem of the thermal X-ray radiation from the hot polar caps of radio pulsars that show evidence of ExB subpulse drift in radio band. In our recent Paper I, using 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 so-called carousel rotation time P₄, reflecting the ExB plasma drift, and the thermal X-ray luminosity L_xfrom the hot polar cap are known. To test the model we used only two 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 this Letter we consider two more pulsars: PSRs B0656+14 and B0628-28, the data for which have recently become available. In PSR B0656+14 the thermal radiation from the hot polar cap was clearly detected, and PSR B0628-28 also seems to have such a component.

In all cases for which both P₄ and L_xare 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 L_x and too low P₄, while the space charge limited model predicts too low L_x and the origin of the subpulse drift has no natural explanation.