Fermi Large Area Telescope First Source Catalog

Abstract

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 MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

“…The original sample of 1158 sources monitored by OVRO (Richards et al 2011) were selected from the Candidate Gamma-Ray Blazar Survey (CGRaBS, Healey et al 2008); these CGRaBS sources were selected to have spectral indices, radio flux densities and X-ray flux densities similar to sources with EGRET gamma-ray detections, such that they would have a high chance of being detected in gamma-rays by Fermi. After the release of the Fermi -LAT catalogue, an additional ∼ 400 gamma-ray detected sources from the First LAT AGN Catalogue (1LAC, Abdo et al 2010) were added to the OVRO monitoring sample. For this present paper, we focus only on the radio-selected CGRaBS sources from the Richards et al (2011) sample, since we are interested in understanding the variability characteristics of radio-selected AGNs.…”

Classification and Ranking of Fermi Lat Gamma-Ray Sources From the 3fgl Catalog Using Machine Learning Techniques

“…Pulsars tend to be non-variable (on long timescales) and have spectra with more curvature, breaking at both ends, and therefore poorly described by a simple power law, normally requiring the addition of an exponential cutoff at a few GeV. This was illustrated graphically in the 1FGL catalog by means of a variability-curvature plot (see Figure 8 from Abdo et al 2010), showing pulsars and AGNs clustering in opposite corners. Indeed, a number of bright pulsar candidates were identified this way(e.g., Kong et al 2012;Romani 2012) and Figure 1.…”

“…Known as the Bright Source List (also referred to as 0FGL, Abdo et al 2009c), this list represented a big improvement over previous catalogs, as illustrated by the fact that fewer than 20% of 0FGL sources were unassociated 7 at the time of publication. 8 Fully fledged Fermi LAT catalogs have been released periodically since then, based on 11 months(1FGL, Abdo et al 2010), two years(2FGL, Nolan et al 2012), and most recently, four years of data(3FGL, Acero et al 2015a). The number of known (>100 MeV) gamma-ray sources now stands at over 3000, with approximately one third of these in the unassociated category (Acero et al 2015a).…”

Basic properties of Fermi blazars and the ‘blazar sequence’

“…Relativistic beaming of radiation is generally invoked to explain the extreme properties (Madau, Ghisellini & Persic 1987). Since the launch of the Fermi satellite, we have entered in a new era of blazars research (Abdo et al 2009a(Abdo et al , 2010a(Abdo et al , 2012. Up to now, the Large Area Telescope (LAT) has detected hundreds of blazars because it has about 20 fold better sensitivity than its predecessor EGRET in the 0.1−100 GeV energy rang.…”