Identifying potentially missed extended sources in the Fermi-LAT 4FGL Catalog using clustering analysis
Abstract
Many Fermi Large Area Telescope (LAT) sources remain unassociated. Some may be extended sources represented by multiple catalog entries, as found for HESS J1813-178. We search for clusters of unassociated Fermi-LAT sources and test whether single extended-source models describe them better than multiple catalog sources. We applied DBSCAN to 4FGL sources with a linking scale of 0.3∘ over 5 GeV-1 TeV. Each cluster contains at least one unassociated source and up to one extended or point-like associated source from selected categories, including pulsars, pulsar wind nebulae and supernova remnants. Using Fermipy, we compared extended- and multiple-source models and characterized each candidate spectrally and morphologically, focusing on the Galactic plane. We identified 48 clusters containing 124 sources, each with at least one unassociated source. For all 8 clusters passing our quality selection, an extended-source model is statistically preferred. At linking scales of 0.4∘ and 0.5∘, all 8 clusters retain their core sources. Cross-matches with the Second Fermi Galactic Extended Sources Catalog (2FGES) and the HESS Galactic Plane Survey (HGPS) showed that 5 clusters overlap known extended sources. The other 3 clusters, including one cluster with a morphology dependent on the interstellar emission model, have no counterpart in either catalog and are new extended-source candidates. Spatial clustering combined with likelihood-based model comparison can uncover extended sources missed in the Fermi-LAT catalog and complements existing searches.
Versions
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BibTeX
@misc{cozzolongo2026identifying,
title = {{Identifying potentially missed extended sources in the Fermi-LAT 4FGL Catalog using clustering analysis}},
author = {Giovanni Cozzolongo and Alison M. W. Mitchell and Samuel T. Spencer and Dmitry V. Malyshev and Tim Unbehaun},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.12776},
eprint = {2607.12776},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.12776},
}
RIS
TY - UNPB
TI - Identifying potentially missed extended sources in the Fermi-LAT 4FGL Catalog using clustering analysis
AU - Giovanni Cozzolongo
AU - Alison M. W. Mitchell
AU - Samuel T. Spencer
AU - Dmitry V. Malyshev
AU - Tim Unbehaun
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2607.12776
UR - https://arxiv.org/abs/2607.12776
AB - Many Fermi Large Area Telescope (LAT) sources remain unassociated. Some may be extended sources represented by multiple catalog entries, as found for HESS J1813-178. We search for clusters of unassociated Fermi-LAT sources and test whether single extended-source models describe them better than multiple catalog sources. We applied DBSCAN to 4FGL sources with a linking scale of 0.3^∘ over 5 GeV-1 TeV. Each cluster contains at least one unassociated source and up to one extended or point-like associated source from selected categories, including pulsars, pulsar wind nebulae and supernova remnants. Using Fermipy, we compared extended- and multiple-source models and characterized each candidate spectrally and morphologically, focusing on the Galactic plane. We identified 48 clusters containing 124 sources, each with at least one unassociated source. For all 8 clusters passing our quality selection, an extended-source model is statistically preferred. At linking scales of 0.4^∘ and 0.5^∘, all 8 clusters retain their core sources. Cross-matches with the Second Fermi Galactic Extended Sources Catalog (2FGES) and the HESS Galactic Plane Survey (HGPS) showed that 5 clusters overlap known extended sources. The other 3 clusters, including one cluster with a morphology dependent on the interstellar emission model, have no counterpart in either catalog and are new extended-source candidates. Spatial clustering combined with likelihood-based model comparison can uncover extended sources missed in the Fermi-LAT catalog and complements existing searches.
ER -