Role of Beam Geometry in Population Statistics and Pulse Profiles of Radio and Gamma-Ray Pulsars

• Published in: The Astrophysical journal 2004-04, Vol.604 (2), p.775-790
• Main Authors: Gonthier, Peter L, Van Guilder, Robert, Harding, Alice K
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Late stages of stellar evolution (including black holes); Pulsars; Stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/382070

We present results of a pulsar population synthesis study that incorporates a number of recent developments and some significant improvements over our previous study. We have included the results of the Parkes multibeam pulsar survey in our select group of nine radio surveys, doubling our sample of radio pulsars. More realistic geometries for the radio and gamma-ray beams are included in our Monte Carlo computer code, which simulates the characteristics of the Galactic population of radio and gamma-ray pulsars. We adopted with some modifications the radio-beam geometry of Arzoumanian, Chernoff, and Cordes. For the gamma-ray beam, we have assumed the slot gap geometry described in the work of Muslimov and Harding. To account for the shape of the distribution of radio pulsars in the [image]-P diagram, we continue to find that decay of the magnetic field on a timescale of 2.8 Myr is needed. With all nine surveys, our model predicts that EGRET should have seen seven radio-quiet (below the sensitivity of these radio surveys) and 19 radio-loud gamma-ray pulsars. AGILE (nominal sensitivity map) is expected to detect 13 radio-quiet and 37 radio-loud gamma-ray pulsars, while GLAST, with greater sensitivity, is expected to detect 276 radio-quiet and 344 radio-loud gamma-ray pulsars. When the Parkes multibeam pulsar survey is excluded, the ratio of radio-loud to radio-quiet gamma-ray pulsars decreases, especially for GLAST. The decrease for EGRET is 45%, implying that some fraction of EGRET unidentified sources are radio-loud gamma-ray pulsars. In the radio geometry adopted, short-period pulsars are core dominated. Unlike the EGRET gamma-ray pulsars, our model predicts that when two gamma-ray peaks appear in the pulse profile, a dominant radio core peak appears in between the gamma-ray peaks. Our findings suggest that further improvements are required in describing both the radio and gamma- ray geometries.