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FSSC: Data : Data Access : LAT 16-year Source List

LAT 16-year Source List (FL16Y)

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 early version (FL16Y, for Fermi LAT 16 Years) of the upcoming 5FGL catalog of LAT sources, based on 16 years of survey data in the 50 MeV-1 TeV energy range. For a full explanation about the catalog and its construction see the FL16Y document. The FL16Y 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 FL16Y JHHMM.m+DDMM(e,i,s,A,B). The optional "e", "i", "s", "A" and "B" designators are explained in the caveats below.

FL16Y Source List Data Products

The 16-year Source List 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.

We emphasize several important points and caveats regarding use of the FL16Y Source List:
  • This work is a summary of the LAT results covering the time period August 4, 2008, to August 2, 2024.
  • 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 source list 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 source list has 7220 sources.
  • The corresponding energy flux limit varies according to the hardness of the source spectrum and the brightness of the background Galactic diffuse emission.
  • Source List 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 source list analysis assumed point source emission for all but 83 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. Besides the Crab Nebula, three other sources are modeled with two spectral components. The components are designated with "A" (primary) and "B" (secondary).
  • 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 FL16Y 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 FL16Y catalog was developed using the same smooth spatial and spectral rescaling of gll_iem_v07 as the 4FGL-DR4 catalog. 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 FL16Y Source List. Any significant updates will be advertised to the fermi-news mailing list. All changes will be documented in the change log below. For any questions please contact the Fermi helpdesk directly at fermihelp@milkyway.gsfc.nasa.gov

FL16Y Source List Change Log

Rev Date Filename Change Description
1 Feb 27, 2026 gll_psc_v40.fit Initial release.