Observational constraints on pulsar radiation theory

A non-stationary model of the polar gap discharge in pulsars is reviewed and modiied. It is argued that the polar gap is braking down via a number of localized spark discharges, feeding a corresponding subpulse-associated plasma columns in the pulsar magnetosphere. It is demonstrated that each spark occupies a region of the polar cap with a characteristic dimension approximately equal to the height of the gap, which is also a typical distance between sparks. Central spark operates at the local pole of the surface magnetic eld and other sparks perform more or less ordered circumferential motion around it due to the modiied EB drift. The core components in pulsar prooles are associated with a central spark while conal components reeect a ring structure formed by sparks circulating around the local pole. It is shown that such arrangement of the polar cap is supported by P and _ P pulsar data. 1. Polar gap, sparks and structure of the pulsar beam Sparks as primary sources of the subpulse associated plasma columns have been proposed in original version by Ruderman and Sutherland (1975, hereafter RS). Gil et al. 1997 proposed a modiication of the sparking model in a following way: the central discharge occurs at the local surface magnetic pole, where the planes of eld lines converge. This spark should be anchored to the area adjacent to the local pole, due to a quasi-axial symmetry of the planes of eld lines converging towards the polar axis. In fact, in a curved magnetic eld, a spark avalanche develops in a direction opposite to the radius of curvature, thus towards a local pole. Moreover, the E B drift in a crossed electric and magnetic eld will cause circulation of the e ? e + plasma of the polar spark around \itself". It is assumed in this paper that the local surface magnetic eld B s has a multipolar structure with the radius of curvature R 10 6 cm. Some kind of quasi-axial symmetry, similar to dipolar and/or quadrupolar conngurations is also assumed. The lifetime of a spark, i.e. the period needed to develop the corotational charge density within the gap volume occupied by the spark, is very short (10s). However, the polar cap surface beneath the spark is heated up to X-ray temperatures by the back streaming electrons, which ignites an intense thermo-emission. The seed charged particles should cause reappearance of the spark after …