Wide radio beams from γ-ray pulsars

Abstract

We investigate the radio and γ-ray beaming properties of normal and millisecond pulsars (MSPs) by selecting two samples from the known populations. The first, Sample G, contains pulsars which are detectable in blind searches of γ-ray data from the Fermi Large Area Telescope. The second, Sample R, contains pulsars detectable in blind radio searches which have spin-down luminosities Ė >1034 erg s-1. We analyze the fraction of the γ-ray-selected Sample G which have detectable radio pulses and the fraction of the radio-selected Sample R which have detectable γ-ray pulses. Twenty of our 35 Sample G pulsars have already observed radio pulses. This rules out low-altitude polar-cap beaming models if, as is currently believed, γ-ray beams are generated in the outer magnetosphere and are very wide. We further find that, for the highest-Ė pulsars, the radio and γ-ray beams have comparable beaming factors, i.e., the beams cover similar regions of the sky as the star rotates. For lower- Ė γ-ray emitting pulsars, the radio beams have about half of the γ-ray sky coverage. These results suggest that, for high- young and MSPs, the radio emission originates in wide beams from regions high in the pulsar magnetosphere, probably close to the null-charge surface and to the γ-ray emitting regions. Furthermore, it suggests that for these high- Ė pulsars, as in the γ-ray case, features in the radio profile represent caustics in the emission beam pattern. © 2010. The American Astronomical Society. All rights reserved.