THE FIRST FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS

Abstract

The dramatic increase in the number of known gamma-ray pulsars since the launch of the Fermi Gamma-ray Space Telescope (formerly GLAST) offers the first opportunity to study a sizable population of these high-energy objects. This catalog summarizes 46 high-confidence pulsed detections using the first six months of data taken by the Large Area Telescope (LAT), Fermi's main instrument. Sixteen previously unknown pulsars were discovered by searching for pulsed signals at the positions of bright gamma-ray sources seen with the LAT, or at the positions of objects suspected to be neutron stars based on observations at other wavelengths. The dimmest observed flux among these gamma-ray-selected pulsars is 6.0 × 10 −8 ph cm −2 s −1 (for E >100 MeV). Pulsed gamma-ray emission was discovered from twenty-four known pulsars by using ephemerides (timing solutions) derived from monitoring radio pulsars. Eight of these new gamma-ray pulsars are millisecond pulsars. The dimmest observed flux among the radio-selected pulsars is 1.4 × 10 −8 ph cm −2 s −1 (for E >100 MeV). The remaining six gamma-ray pulsars were known since the Compton Gamma Ray Observatory mission, or before. The limiting flux for pulse detection is non-uniform over the sky owing to different background levels, especially near the Galactic plane. The pulsed energy spectra can be described by a power law with an exponential cutoff, with cutoff energies in the range ∼ 1 − 5 GeV. The rotational energy loss rate (Ė) of these neutron stars spans 5 decades, from ∼3 × 10 33 erg s −1 to 5 × 10 38 erg s −1 , and the apparent efficiencies for conversion to gamma-ray emission range from ∼ 0.1% to ∼ unity, although distance uncertainties complicate efficiency estimates. The pulse shapes show substantial

PSRs J0248+6021 and J2240+5832: young pulsars in the northern Galactic plane

“…A pure power law (β = 0) describes many gamma-ray sources, such as active galactic nuclei (Abdo et al 2010a). The 46 gamma-ray pulsars discussed in Abdo et al (2010b) are generally well-described by a simple exponential cutoff, β = 1, a shape predicted by outer magnetosphere emission models (see the Discussion, below). Models where gamma-ray emission occurs closer to the neutron star can have sharper "super-exponential" cutoffs, e.g.…”

“…(1)). We set f Ω = 1 as in Abdo et al (2010b), and see below that the emission models in any case yield f Ω 1. Defining G 11 = 10 −11 erg cm −2 s −1 and d 1 = 1 kpc = 3.1 × 10 21 cm gives L γ = 1.2 × 10 33 f Ω (G 100 /G 11 )(d/d 1 ) 2 erg s −1 .…”

“…6 of the Fermi Pulsar Catalog (Abdo et al 2010b), L h γ = 10 33 Ė /10 33 erg/s, where h stands for "heuristic". For theĖ of our two pulsars, L h γ is 1.5 × 10 34 erg s −1 , very near L γ obtained for PSR J0248+6021.…”

“…Indeed, PSR J0248+6021 is among the 46 gamma-ray pulsars described in the "First Pulsar Catalog" (Abdo et al 2010b) using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). They have the same magnetic field strengths at the neutron-star light cylinder, B LC , to within 20%, and the characteristic ages τ c = P/2Ṗ differ by only a factor of two.…”

Luminosity Evolution of Rotation-Powered, High-Energy Pulsars

“…Thanks to its superb sensitivity, the number of gamma-ray pulsars has increased from six in Compton Gamma Ray Observatory era to more than one hundred. Plotting their best estimate of the gamma-ray luminosity, L  , against the spin-down luminosity, L spin , [1] found an important relation 0.5 spin LL   ( fig. 1).…”