Megan E. DeCesar

Three Millisecond Pulsars in FERMI LAT Unassociated Bright Sources

We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. We report the discovery of three radio and γ-ray millisecond pulsars (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind γ-ray pulsation searches. They seem to be relatively normal, nearby (≤2 kpc) MSPs. These observations, in combination with the Fermi detection of γ-rays from other known radio MSPs, imply that most, if not all, radio MSPs are efficient γ-ray producers. The γ-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few GeV, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Their soft X-ray luminosities of ~1030-1031 erg s–1 are typical of the rare radio MSPs seen in X-rays.

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 Be/X-RAY BINARY SWIFT J1626.6-5156 AS A VARIABLE CYCLOTRON LINE SOURCE

Swift J1626.6−5156 is a Be/X-ray binary that was in outburst from 2005 December until 2008 November. We have examined Rossi X-ray Timing Explorer/Proportional Counter Array (PCA) and High Energy X-ray Timing Explorer spectra of three long observations of this source taken early in its outburst, when the PCA 2–20 keV count rate was >70 counts s −1 PCU −1 , as well as several combined observations from different stages of the outburst. The spectra are best fit with an absorbed cutoff power law with a ∼6.4 keV iron emission line and a Gaussian optical depth absorption line at ∼10 keV. We present strong evidence that this absorption-like feature is a cyclotron resonance scattering feature, making Swift J1626.6−5156 a new candidate cyclotron line source. The redshifted energy of ∼10 keV implies a magnetic field strength of ∼8.6(1 + z) × 10 11 G in the region of the accretion column close to the magnetic poles where the cyclotron line is produced. Analysis of phase-averaged spectra spanning the duration of the outburst suggests a possible positive correlation between the fundamental cyclotron energy and source luminosity. Phase-resolved spectroscopy from a long observation reveals a variable cyclotron line energy, with phase dependence similar to a variety of other pulsars, as well as the first harmonic of the fundamental cyclotron line.

Likelihood Analysis of High‐Energy Pulsar Emission Models

The high‐quality Fermi LAT observations of gamma‐ray pulsars open a new window to understanding the generation mechanisms of high‐energy pulsar emission. To explore this, we have simulated high‐energy light curves from geometrical representations of the outer gap and slot gap emission models with the vacuum retarded dipole magnetosphere model. These simulated light curves are compared with the LAT light curves of the Vela and Geminga pulsars via maximum likelihood, using a Markov Chain Monte Carlo method to explore the models’ phase space.