Most pulsars observed by the Fermi Large Area Telescope have γ-ray luminosities scaling with spin-down power as . However, there exist one detection and several upper limits an order of magnitude or more fainter than this trend. We describe these "sub-luminous" γ-ray pulsars and discuss the case for this being an orientation effect. Of the 12 known young radio pulsars with and d ⩽ 2 kpc several are substantially sub-luminous. The limited available geometrical constraints favor aligned geometries for these pulsars, although no one case for alignment is compelling. In this scenario GeV emission detected from such sub-luminous pulsars can be due to a lower altitude, lower-power accelerator gap.
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Romani et al. (2011) studied this question.