WIDE RADIO BEAMS FROM γ-RAY PULSARS

We investigate the radio and gamma-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 gamma-ray data from the Fermi Large Area Telescope. The second, Sample R, contains pulsars detectable in blind radio searches which have spin-down luminosities (E) over dot > 10(34) erg s(-1). We analyze the fraction of the gamma-ray-selected Sample G which have detectable radio pulses and the fraction of the radio-selected Sample R which have detectable gamma-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, gamma-ray beams are generated in the outer magnetosphere and are very wide. We further find that, for the highest-(E) over dot pulsars, the radio and gamma-ray beams have comparable beaming factors, i.e., the beams cover similar regions of the sky as the star rotates. For lower-(E) over dot gamma-ray emitting pulsars, the radio beams have about half of the gamma-ray sky coverage. These results suggest that, for high-(E) over dot 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 gamma-ray emitting regions. Furthermore, it suggests that for these high-(E) over dot pulsars, as in the gamma-ray case, features in the radio profile represent caustics in the emission beam pattern.