Fermi Gamma-ray Space Telescope

LAT 10-year Source Catalog (4FGL-DR2)

The Large Area Telescope (LAT) on board NASA's Fermi Gamma-ray Space Telescope (launched June 11, 2008) surveys the entire sky each day. This web page presents an incremental version (4FGL-DR2, for Data Release 2) of the fourth full catalog of LAT sources, based on 10 years of survey data in the 50 MeV-1 TeV energy range. For a full explanation about the catalog and its construction see the document.

The source designation is the same as 4FGL, 4FGL JHHMM.m+DDMM(c,e,i,s) where the 4 refers to the fourth catalog (1FGL was released at 1 year, 2FGL at 2 years, and 3FGL at 4 years) and FGL represents Fermi Gamma-ray LAT. In 4FGL-DR2, the "DataRelease" column set to either 1 or 2 allows telling new sources from original 4FGL sources. The optional "e", "i" and "s" designators are explained in the caveats below. The 4FGL-DR2 does not include 2-month light curves that were in the 4FGL catalog.

LAT Catalog Data Products

The LAT 10-year Source Catalog is currently available as a FITS file to be used for data analysis within the Fermitools. A BROWSE table containing a searchable version of the catalog is also available. Supporting tools and documentation have been provided and are linked below.

  • LAT 10-year Source Catalog (4FGL-DR2 in FITS format)
  • LAT 10-year Source Catalog (BROWSE table - Ongoing update)
  • LAT 10-year Source Catalog (XML format)
  • LAT 10-year Source Catalog Document
  • Map of the 10-year LAT Detection Threshold (in FITS format)
  • Python script (and instructions) to convert the 4FGL-DR2 source list into an XML file.
  • DS9 Region Files:
  • Extended Source template archive – Gzipped archive of extended source templates used in the catalog analysis.
  • Sun/Moon template model files: Only for use with the 10-year data set!
  • Plots of spectral fits for 4FGL-DR2 sources: Gzipped file
  • Plots of 1-year light curves for 4FGL-DR2 sources: Gzipped file
  • Aperture photometry light curves and power spectra
  • We emphasize several important points and caveats regarding use of the 4FGL-DR2 catalog:

    • This work is a summary of the LAT results covering the time period August 4, 2008, to August 2, 2018.
    • The analysis is based on data in the 50 MeV to 1 TeV energy range.
    • Source detection is based on the integrated data set, i.e., sources are detected according to their average fluxes.
    • The catalog adopted multiple spectral shapes, depending on the observed source properties. Pulsars are modeled by an exponentially cutoff Power Law. Others are modeled as a LogParabola if statistically significant curvature (according to Signif_Curve) is detected, or as a simple Power Law otherwise.
    • After computing the maximum likelihood, the threshold for inclusion of new sources is likelihood Test Statistic TS > 25, corresponding to somewhat more than 4 sigma significance. The catalog has 5787 sources. Original 4FGL sources are retained in the 4FGL-DR2 even if TS < 25
    • The corresponding energy flux limit varies according to the hardness of the source spectrum and the brightness of the background Galactic diffuse emission.
    • Catalog entries include quality flags that indicate potential issues: any non-zero entry in the "Flags" column indicates that the source is affected by systematic errors (see the table in the preprint for details). Sources with these indicators should be used with great care. They correspond to significant excesses of photons, but such excesses can result from residual extended emission or confused source pile-up.
    • The catalog analysis assumed point source emission for all but seventy-five extended sources, which were modeled using spatial templates and are indicated by an "e" following the name. Results for extended sources such as the LMC and Cen A lobes are likely to not be representative of the total emission, and additional catalog point sources may appear near such objects.
    • The Crab pulsar and PWN are represented by a total of three entries, two of which (designated "i" for inverse compton and "s" for synchrotron) represent spectral components of the PWN. We consider these three entries to represent two sources.
    • 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 alignment between known and candidate gamma-ray producing objects with 4FGL-DR2 sources. Upper case in the CLASS1 column means identified. Except for those cases with correlated variability or spatial extent, a physical relationship is not established. The designators for some associated sources may be updated in a future release to use more common or more complete names.

    Feedback about the catalog and document should be directed to the contact authors. Ongoing efforts to understand the calibration and improve the analysis techniques may lead to updates to the 4FGL-DR2 catalog. Any significant updates will be advertised to the fermi-news mailing list. All changes will be documented in the change log below.

    4FGL-DR2 Source List Change Log

    Rev Date Filename Change Description
    1 22 May 2020 gll_psc_v23.fit Initial Release
    2 10 September 2020 gll_psc_v24.fit Optical classifications of 132 more sources, previously blazars of unknown type