Fermi Gamma-ray Space Telescope

LAT 1-year Source Catalog

The Fermi Gamma-ray Space Telescope (Fermi) Large Area Telescope (LAT) is a successor to EGRET, with greatly improved sensitivity, resolution, and energy range. This web page presents the first full catalog of LAT sources, based on the first eleven months of survey data. For a full explanation about the catalog and its construction see the LAT 1-year Catalog Paper

The source designation is 1FGL JHHMM.m+DDMM(c) where the 1 refers to the first catalog (others are planned for years 2 and 5) and FGL represents Fermi Gamma-ray LAT. The optional "c" designator is explained in the caveats below.

LAT Catalog Data Products

The LAT 1-year Source Catalog is currently available as a FITS file and as an XML model file to be used for data analysis within the Fermi Science Tools. It has also been made available as a BROWSE table. Supporting tools and information have also been provided and are linked below.

It is important that all users of this catalog review the caveats listed below the catalog links. These describe the content of the catalog at a high level, as well as some cautions for the user.

LAT Catalog Caveats

Some work on the analysis procedures for data from Fermi LAT is still in progress. In particular, we emphasize several caveats for use of this catalog:

  • This work is a summary of the LAT results covering the time period August, 2008, to July, 2009.
  • The analysis is based on data in the 100 MeV to 100 GeV energy range.
  • Source detection is based on the integrated data set, i.e., sources are detected according to their average fluxes. Note that all of the bright flaring sources that have been announced via Astronomer's Telegrams are also detected in the integrated 11-month data set.
  • Adopting a power law spectral shape for each source, and computing the maximum likelihood, the threshold for inclusion is likelihood Test Statistic TS > 25, corresponding to somewhat more than 4 sigma significance. The catalog has 1451 sources.
  • The corresponding flux limit varies widely according to the hardness of the source spectrum and the brightness of the background Galactic diffuse emission.
  • The 1FGL information in five energy bands is not appropriate for detailed spectral modeling. Upper limits are indicated by 0 flux uncertainty; in these cases the corresponding flux entry has a 2-sigma upper limit. Note that some sources have only upper limits in each of the 5 bands; these sources have been detected based on their integrated fluxes. The curvature flag indicates a high probability that the spectrum is not well represented by a single power law.
  • The variability flag indicates high probability that the source is variable on a time scale of months. It does not address shorter or longer time variations.
  • The diffuse model used in the analysis is still subject to improvements. Matching the model to the large-scale emission is an iterative process. The diffuse model is particularly important for sources near the Galactic Plane.
  • Catalog entries include two important quality flags that indicate potential issues: a "c" following the 1FGL name indicates that the source is found in a region with bright and/or possibly incorrectly modeled diffuse emission; any non-zero entry in the "Flags" column indicates that some inconsistency was seen during the analysis (see the table in the preprint for details). Sources with either of these indicators should be used with some care. They may be artifacts of the analysis.
  • The catalog analysis was done assuming point source emission. Results for extended sources such as the LMC and Cen A are likely not to be representative of the total emission, and multiple catalog point sources may appear near such objects.
  • Associations listed in the catalog are not in general to be taken as firm identifications. Associations are positional coincidences that are statistically unlikely to be due to chance between known or candidate gamma-ray producing objects with 1FGL sources. Except for those cases with correlated variability or spatial extent, a physical relationship is not established.
  • The paper includes cross references to related LAT-team publications on a source-by-source basis.

All changes are documented in the change log below.

LAT 1-year Catalog Change Log

Rev Date Filename Change Description
1 14 Jan 2010 gll_psc_v01.fit Initial Release
2 4 Feb 2010 gll_psc_v02.fit Added Unc_Flag_History and ASSOC_TEV columns
Updated association information for several sources
Updated parameters for 1FGL J0801.3-5626
3 9 Feb 2010 gll_psc_v03.fit Added source associated with 1FGL J1934.9+2031c