2 00 4 A model for the challenging “ bi - drifting ” phenomenon in PSR J 0815 + 09

A new drifting pulsar, PSR J0815+09, was discovered in the Arecibo driftscan searches (McLaughlin et al. 2004). An intriguing feature of this source is that within the four pulse components in the integrated pulse profile, the subpulse drifting direction in the two leading components is opposite from that in the two trailing components. In view that the leading theoretical model (Ruderman & Sutherland 1975) for pulsar sub-pulse drifting can only interpret one-direction sub-pulse drifting, the observed bi-drifting phenomenon from PSR J0815+09 poses a great challenge to the pulsar theory. The inner annular gap (IAG), a new type of inner particle accelerator, was recently proposed to explain both γ-ray and radio emission from pulsars (Qiao et al. 2004). Here we show that the coexistence of the IAG and the conventional inner core gap (ICG) offers a natural interpretation to the bi-drifting phenomenon. In particular, the peculiar drifting behavior in PSR J0815+09 can be reproduced within the inverse Compton scattering (ICS) model for pulsar radio emission. Subject headings: pulsars: general — pulsars: individual (PSR J0815+09) — radiation mechanisms: non-thermal — stars: neutron — elementary particles