High-energy gamma-ray observations of two young, energetic radio pulsars

We present results of Compton Gamma-Ray Observatory/EGRET observations of the unidentified high-energy gamma-ray sources 2EG J1049--5847 (GEV J1047--5840, 3EG J1048--5840) and 2EG J1103--6106 (3EG J1102--6103). These sources are spatially coincident with the young, energetic radio pulsars PSRs B1046--58 and J1105--6107, respectively. We find evidence for an association between PSR B1046--58 and 2EG J1049 - 5847. The gamma-ray pulse profile, obtained by folding time-tagged photons having energies above 400 MeV using contemporaneous radio ephemerides, has probability of arising by chance of 1.2 x 10(-4) according to the binning-independent H-test. A spatial analysis of the on-pulse photons reveals a point source of equivalent significance 10.2 sigma. Off-pulse, the significance drops to 5.8 sigma. Archival ASCA data show that the only hard X-ray point source in the 95% confidence error box of the gamma-ray source is spatially coincident with the pulsar within the 1' uncertainty (Pivovaroff, Kaspi, & Gotthelf). The double peaked gamma-ray pulse morphology and leading radio pulse are similar to those seen for other gamma-ray pulsars and are well explained in models in which the gamma-ray emission is produced in charge-depleted gaps in the outer magnetosphere. The inferred pulsed gamma-ray flux above 400 MeV, (2.5 +/- 0.6) x 10(-10) ergs cm(-2) s(-1), represents 0.011 +/- 0.003 of the pulsar's spin-down luminosity, for a distance of 3 kpc and 1 sr beaming. For PSR J1105--6107, light curves obtained by folding EGRET photons using contemporaneous radio ephemerides show no significant features. We conclude that this pulsar converts less than 0.014 of its spin-down luminosity into E > 100 MeV gamma-rays beaming in our direction (99% confidence), assuming a distance of 7 kpc, 1 sr beaming and a duty cycle of 0.5.