We present a catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), during the first 11 months of the science phase of the mission, which began on 2008 August 4. The First Fermi-LAT catalog (1FGL) contains 1451 sources detected and characterized in the 100 MeV to 100 GeV range. Source detection was based on the average flux over the 11 month period, and the threshold likelihood Test Statistic is 25, corresponding to a significance of just over 4σ. The 1FGL catalog includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and power-law spectral fits as well as flux measurements in five energy bands for each source. In addition, monthly light curves are provided. Using a protocol defined before launch we have tested for several populations of gamma-ray sources among the sources in the catalog. For individual LAT-detected sources we provide firm identifications or plausible associations with sources in other astronomical catalogs. Identifications are based on correlated variability with counterparts at other wavelengths, or on spin or orbital periodicity. For the catalogs and association criteria that we have selected, 630 of the sources are unassociated. Care was taken to characterize the sensitivity of the results to the model of interstellar diffuse gamma-ray emission used to model the bright foreground, with the result that 161 sources at low Galactic latitudes and toward bright local interstellar clouds are flagged as having properties that are strongly dependent on the model or as potentially being due to incorrectly modeled structure in the Galactic diffuse emission.

The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey is a new survey of Galactic 13 CO J ¼ 1 ! 0 emission. The survey used the SEQUOIA multipixel array on the Five College Radio Astronomy Observatory 14 m telescope to cover a longitude range of l ¼ 18 55N7 and a latitude range of jbj < 1 , a total of 75.4 deg 2 . Using both position-switching and On-The-Fly mapping modes, we achieved an angular sampling of 22 00 , better than half of the telescope's 46 00 angular resolution. The survey's velocity coverage is À5 to 135 km s À1 for Galactic longitudes l 40 and À5 to 85 km s À1 for Galactic longitudes l > 40 . At the velocity resolution of 0.21 km s À1 , the typical rms sensitivity is (T Ã A ) $ 0:13 K. The survey comprises a total of 1,993,522 spectra. We show integrated intensity images (zeroth moment maps), channel maps, position-velocity diagrams, and an average spectrum of the completed survey data set. We also discuss the telescope and instrumental parameters, the observing modes, the data reduction processes, and the emission and noise characteristics of the data set. The Galactic Ring Survey data are available to the community online or in DVD form by request.

Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the γ-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than ∼10σ) γ-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) γ-ray sources in the early mission data.

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

Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants