Pulsed high-energy emission from striped pulsar winds

Abstract

In the general case of a neutron star where the magnetic and rotation axes are not aligned, the pulsar wind will have an equatorial zone of alternating magnetic polarity, the so-called “striped” wind region. Beyond some critical radius, reconnection might occur in the current sheet separating the “stripes” of oppositely directed magnetic field, thereby heating the sheet particles and accelerating the wind. For typical pulsar wind parameters, the synchrotron emission from these heated particles will appear pulsed [Space Sci. Rev. 24 (1979) 437; Astron. Astroph. 388 (2002) L29], with in general two peaks whose phase separation will depend on the pulsar's magnetic axis inclination and viewing angle. We present a model which can readily account for the peak separation in the high-energy emission from the Crab and Vela pulsars. Furthermore, we discuss the synchrotron emissivity of the reconnecting current sheet, and the spectral properties which result for various reconnection recipes. For wind parameters thought appropriate for the Crab pulsar, the observed pulsed luminosity at optical and higher energies can be reproduced if reconnection occurs sufficiently fast. We conclude that this “wind sheet” model is a viable alternative to the usual polar cap and outer gap models [Proc. Am. Inst. Phys. 558 (2001) 115] of pulsar high-energy emission.