A new drifting pulsar, PSR J0815+09, was discovered in the Arecibo drift-scansearches. An intriguing feature of this source is that within the four pulsecomponents in the integrated pulse profile, the sub-pulse drifting direction inthe two leading components is opposite from that in the two trailingcomponents. In view that the leading theoretical model for pulsar sub-pulsedrifting can only interpret one-direction sub-pulse drifting, the observed"bi-drifting" phenomenon from PSR J0815+09 poses a great challenge to thepulsar theory. The inner annular gap (IAG), a new type of inner particleaccelerator, was recently proposed to explain both $\gamma$-ray and radioemission from pulsars. Here we show that the coexistence of the IAG and theconventional inner core gap (ICG) offers a natural interpretation to thebi-drifting phenomenon. In particular, the peculiar drifting behavior in PSRJ0815+09 can be reproduced within the inverse Compton scattering (ICS) modelfor pulsar radio emission.
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