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A. K. Harding (NASA/GSFC), Z. Arzoumanian (USRA-NASA/GSFC), P. Gonthier (Hope College), J. M. Cordes (Cornell Univ.)
A number of very young and energetic pulsars have recently been discovered as a result of deep radio searches of X-ray point sources in or near supernova remnants. These pulsars have unusually low radio luminosities, well below the luminosities of previously known young pulsars. Their pulse profiles show single, broad peaks and duty cycles of 10%-30%. We explore the possibility that the line-of-sight intersects the outer edge of a conal beam at large impact parameter. Using the measured radio flux and pulse FWHM for six pulsars, and the radio emission geometry and luminosity law proposed by Arzoumanian et al. (2002), both the viewing angle and magnetic inclination angle with respect to the rotation axis can be uniquely determined. We find that most of the pulsars must have small magnetic inclination angles, with five out of six having inclination less than around 30 degrees. The low luminosities of these pulsars may thus be consistently explained by a relatively large and off-beam viewing angle, rather than by an intrinsically low luminosity, supporting the idea that the apparent dispersion in pulsar radio luminosities is largely a result of viewing angle. It also can explain the high incidence of young pulsar detections and provides hope that more very young pulsars may be discovered at the positions of X-ray point sources. The fact that these young pulsars have small inclination angles may have interesting implications for the magnetic field evolution of neutron stars. The apparent widths of pulsar beams suggest also that many pulsars will be totally radio quiet because the emissivity falls very sharply with polar angle.
Bulletin of the American Astronomical Society,
35#2
© 2003. The American Astronomical Soceity.