Fermi Gamma-ray Space Telescope

LAT 14-year Source Catalog (4FGL-DR4)

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-DR4, for Data Release 4) of the fourth full catalog of LAT sources, based on 14 years of survey data in the 50 MeV-1 TeV energy range. For a full explanation about the catalog and its construction see the DR4 document . The DR4 data analysis is similar to 4FGL-DR3 (with a few differences explained in the text), so the reference is still the DR3 paper . Please cite both documents when you use this data release.

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. The "DataRelease" column set to either 1, 2, 3 or 4 tells when a source was introduced in the catalog. The optional "e", "i" and "s" designators are explained in the caveats below.

LAT Catalog Data Products

The LAT 14-year Source Catalog is currently available as a FITS file to be used for data analysis within the Fermitools. Supporting tools and documentation have been provided and are linked below.

  • LAT 14-year Source Catalog (4FGL-DR4 in FITS format)
  • LAT 14-year Source Catalog (BROWSE table)
  • LAT 14-year Source Catalog (XML format)
  • LAT 14-year Source Catalog Paper
  • Map of the 14-year LAT Detection Threshold (in FITS format)
  • Python script (and instructions) to convert the 4FGL-DR4 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 14-year data set!
  • Plots of spectral fits for 4FGL-DR4 sources: Gzipped file
  • Plots of 1-year light curves for 4FGL-DR4 sources: Gzipped file
  • List of catalogs used for the associations of 4FGL-DR4 sources: pdf file

    • We emphasize several important points and caveats regarding use of the 4FGL-DR4 catalog:

    • This work is a summary of the LAT results covering the time period August 4, 2008, to August 2, 2022.
    • 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 7194 sources. All previous 4FGL sources (except for a few discussed in the paper) are retained in the 4FGL-DR4 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 82 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-DR4 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.
    • The DR4 catalog was developed using a smooth spatial and spectral rescaling of the 4FGL Galactic diffuse model gll_iem_v07, as explained in Sect 2.2 of the document. The adjustment is largely equivalent to modulating the gll_iem_v07 model with a LogParabola spectral shape in each region of interest. It is not recommended as an all-purpose replacement for gll_iem_v07 because its behavior above 10 GeV was not carefully controlled, but it can be used in the GeV domain following the DR4 prescription (modulated by a power law and associated with the fixed isotropic spectrum and the DR4 background of sources). When using it, please quote "the rescaled gll_iem_v07 interstellar emission model associated to the 4FGL-DR4 catalog" and cite the DR4 document (link to document). This rescaled diffuse model has the same limitations as gll_iem_v07, and comparing results obtained with this rescaled model and with gll_iem_v07 cannot quantify systematic errors due to the model of the diffuse emission.

    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-DR4 catalog. Any significant updates will be advertised to the fermi-news mailing list. All changes will be documented in the change log below.

    4FGL-DR4 Source List Change Log

    Rev Date Filename Change Description
    1 24 July 2023 gll_psc_v32.fit Initial Release
    2 20 Nov 2023 gll_psc_v33.fit Corrects values of LP_SigCurv and PLEC_SigCurv incorrectly set to 0 in 4 sources.
    3 22 Feb 2024 gll_psc_v34.fit Set localization uncertainties of 21 unpublished pulsars to 0.1; Reinstate 31 forgotten low-confidence associations, remove one and upgrade two (4FGL J0153.3-1845 and 4FGL J2306.6+0940) to high-confidence.