Understanding the nature of drifting subpulses in pulsars.

© ASTRON

We performed detailed analysis of archival data of PSR J0815+0939 which revealed that the second component is the only one which exhibits drift in the opposite direction. We proposed a model that shows that the observed bi-drifting phenomenon follows from the insight that the discharging regions, i.e., sparks, do not rotate around the magnetic axis per se, but rather around the point of maximum potential at the polar cap.

We found that a purely dipolar surface magnetic field cannot exhibit bi-drifting behaviour, however, certain non-dipolar configurations can. We can distinguish two types of solutions, with relatively low (~1e12 G) and high (~1e14 G) surface magnetic fields. Depending on the strength of the surface magnetic field, the radius of the curvature of magnetic field lines ranges from 1e5 to 1e7 cm.

Pulsar J0815+0939 allows us to gain an understanding of the polar-cap conditions essential for plasma generation processes in the inner acceleration region, by linking the observed subpulse shift to the underlying spark motion. (Szary & van Leeuwen, ApJ 845, 95).