PSR J0007+7303 IN THE CTA1 SUPERNOVA REMNANT: NEW GAMMA-RAY RESULTS FROM TWO YEARS OF FERMI LARGE AREA TELESCOPE OBSERVATIONS

One of the main results of the Fermi Gamma-Ray Space Telescope is the discovery of gamma-ray selected pulsars. The high magnetic field pulsar, PSR J0007+7303 in CTA1, was the first ever to be discovered through its gamma-ray pulsations. Based on analysis of two years of Large Area Telescope (LAT) survey data, we report on the discovery of gamma-ray emission in the off-pulse phase interval at the similar to 6 sigma level. The emission appears to be extended at the similar to 2 sigma level with a disk of extension similar to 0.degrees 6. level. The flux from this emission in the energy range E >= 100 MeV is F-100 = (1.73 +/- 0.40(stat) +/- 0.18(sys)) x 10(-8) photons cm(-2) s(-1) and is best fitted by a power law with a photon index of Gamma = 2.54 +/- 0.14(stat) +/- 0.05(sys). The pulsed gamma-ray flux in the same energy range is F-100 = (3.95 +/- 0.07(stat) +/- 0.30(sys)) x 10 (7) photons cm (2) s (1) and is best fitted by an exponentially cutoff power-law spectrum with a photon index of Gamma = 1.41 +/- 0.23(stat) +/- 0.03(sys) and a cutoff energy E-c = 4.04 +/- 0.20(stat) +/- 0.67(sys) GeV. We find no flux variability either at the 2009 May glitch or in the long-term behavior. We model the gamma-ray light curve with two high-altitude emission models, the outer gap and slot gap, and find that the preferred model depends strongly on the assumed origin of the off-pulse emission. Both models favor a large angle between the magnetic axis and observer line of sight, consistent with the nondetection of radio emission being a geometrical effect. Finally, we discuss how the LAT results bear on the understanding of the cooling of this neutron star.