A. A. Abdo

OBSERVATIONS OF ENERGETIC HIGH MAGNETIC FIELD PULSARS WITH THE FERMI LARGE AREA TELESCOPE

We report the detection of γ-ray pulsations from the high-magnetic-field rotation-powered pulsar PSR J1119 6127 using data from the Fermi Large Area Telescope. The γ-ray light curve of PSR J1119 6127 shows a single, wide peak offset from the radio peak by 0.43±0.02 in phase. Spectral analysis suggests a power law of index 1.0 ± 0.3 +0.4 −0.2 with an energy cut-off at 0.8 ± 0.2 +2.0 −0.5 GeV. The first uncertainty is statistical and the second is systematic. We discuss the emission models of PSR J1119 6127 and demonstrate that despite the object’s high surface magnetic field—near that of magnetars—the field strength and structure in the γ-ray emitting zone are apparently similar to those of typical young pulsars. Additionally, we present upper limits on the γ-ray pulsed emission for the magnetically active PSR J1846 0258 in the supernova remnant Kesteven 75 and two other energetic high-B pulsars, PSRs J1718 3718 and J1734 3333. We explore possible explanations for the non-detection of these three objects, including peculiarities in their emission geometry. Subject headings: gamma rays: stars — pulsars: general — pulsars: individual (PSR J1119 6127, PSR J1718 3718, PSR J1734 3333, PSR J1846 0258)

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 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) × 10–8 photons cm–2 s–1 and is best fitted by a power law with a photon index of Γ = 2.54 ± 0.14stat ± 0.05sys. The pulsed γ-ray flux in the same energy range is F 100 = (3.95 ± 0.07stat ± 0.30sys) × 10–7 photons cm–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 ± 0.67sys GeV. 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.

The missing GeV γ-ray binary: searching for HESS J0632+057 with Fermi-LAT

The very high energy (VHE; >100u2009GeV) source HESS J0632+057 has been recently confirmed as a γ-ray binary, a subclass of the high-mass X-ray binary population, through the detection of an orbital period of 321u2009d. We performed a deep search for the emission of HESS J0632+057 in the GeV energy range using data from the Fermi Large Area Telescope (LAT). The analysis was challenging due to the source being located in close proximity to the bright γ-ray pulsar PSR J0633+0632 and lying in a crowded region of the Galactic plane where there is prominent diffuse emission. We formulated a Bayesian block algorithm adapted to work with weighted photon counts, in order to define the off-pulse phases of PSR J0633+0632. A detailed spectral-spatial model of a 5° circular region centred on the known location of HESS J0632+057 was generated to accurately model the LAT data. No significant emission from the location of HESS J0632+057 was detected in the 0.1-100u2009GeV energy range integrating over ∼3.5 yr of data, with a 95 per cent flux upper limit of F0.1-100u2009GeV < 3 × 10− 8 phu2009cm−2u2009s−1. A search for emission over different phases of the orbit also yielded no significant detection. A search for source emission on shorter time-scales (days-months) did not yield any significant detections. We also report the results of a search for radio pulsations using the 100-m Green Bank Telescope. No periodic signals or individual dispersed bursts of a likely astronomical origin were detected. We estimated the flux density limit of < 90/40u2009μJy at 2/9u2009GHz. The LAT flux upper limits combined with the detection of HESS J0632+057 in the 136-400 TeV energy band by the MAGIC collaboration imply that the VHE spectrum must turn over at energies <136u2009GeV placing constraints on any theoretical models invoked to explain the γ-ray emission.