Thermal X-ray Emission from Hot Polar Cap in Radio Pulsars with Drifting Subpulses

Abstract

We consider the problem of thermal X‐ray radiation from the hot polar cap heated by the spark‐associated back‐flow electron bombardment, in radio pulsars showing the subpulse drift. Using the partially screened gap (PSG) model of the inner acceleration region we examine a simple relationship between the drift rate of subpulses observed in a radio‐band (measured as the polar cap carousel circulation time P4, that is the time interval after which sparks complete one full revolution around the polar cap) and the heating rate (measured as thermal X‐ray luminosity Lx from hot polar cap). This relationship reflects the fact that both the drift rate and the heating rate are determined by about the same value of the non‐corotational component of gap electric field. The theoretical formula can be tested for pulsars in which the carousel rotation time P4, and the thermal X‐ray bolometric luminosity Lx from the hot polar cap are known. There are currently four pulsars in which both these quantities and are measured or at least estimated: PSRs B0943+10, B1133+16, B0656+14 and B0628‐28. They all seem to confirm the predictions of the PSG model. This model requires a very strong surface magnetic field in pulsars, exceeding 1014 G irrespective of the dipolar component determined from the spin‐down data.