2011ApJ...738..114R

Most pulsars observed by the Fermi Large Area Telescope have γ-ray luminosities scaling with spin-down power {dot}E as L_γ~. 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 {dot}E>10^{34}  erg s^{-1} 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.