PSR J0007+7303 in the CTA1 supernova remnant: New gamma-ray results from two years of Fermi large area telescope observations

Abstract

One of the main results of the Fermi Gamma-Ray Space Telescope is the discovery of γ-ray selected pulsars. The high magnetic field pulsar, PSR J0007+7303 in CTA1, was the first ever to be discovered through its γ-ray pulsations. Based on analysis of two years of Large Area Telescope (LAT) survey data, we report on the discovery of γ-ray emission in the off-pulse phase interval at the 6σ level. The emission appears to be extended at the 2σ level with a disk of extension 06. level. The flux from this emission in the energy range E ≥ 100 MeV is F 100 = (1.73 ± 0.40stat ± 0.18sys) × 10 -8photonscm-2 s-1 and is best fitted by a power law with a photon index of Γ = 2.54 0.14stat 0.05 sys. The pulsed γ-ray flux in the same energy range is F 100 = (3.95 ± 0.07stat ± 0.30sys) × 10-7photonscm-2 s-1 and is best fitted by an exponentially cutoff power-law spectrum with a photon index of Γ = 1.41 ± 0.23stat ± 0.03sys and a cutoff energy Ec = 4.04 ± 0.20stat ± 0.67 sysGeV. We find no flux variability either at the 2009 May glitch or in the long-term behavior. We model the γ-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. © 2012 The American Astronomical Society. All rights reserved.