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A. K. Harding (NASA Goddard Space Flight Center), B. Zhang (NASA Goddard Space Flight Center, NRC Research Associate)
We investigate whether gamma-ray pulsars viewed at a large angle to the neutron star magnetic pole could contribute to the new population of galactic unidentified EGRET sources associated with the Gould belt. The faint, soft nature of these sources is distinctly different from both the properties of unidentified EGRET sources along the galactic plane and of the known gamma-ray pulsars, all of which are radio loud, with the possible exception of Geminga. We explore the possibility, within the polar cap model, that some of these sources are due to emission from pulsars seen at lines-of sight that miss both the bright gamma-ray double-cone beams and the radio beam. The off-beam gamma-rays come from high-altitude curvature emission of primary particles, are radiated over a large solid angle and have a much softer spectrum than that of the main beams. We estimate that the probability of detecting such off-beam emission is about an order of magnitude higher than that of the on-beam emission at the distance of the Gould Belt. At least some of the radio-quiet Gould belt sources detected by EGRET could therefore be such off-beam gamma-ray pulsars.