arXiv subjects

Giovanni Cozzolongo

Publications and source records attributed to Giovanni Cozzolongo.

3 recordsLinked to original sources

arXiv2026

Identifying potentially missed extended sources in the Fermi-LAT 4FGL Catalog using clustering analysis

Context. Since its launch in 2008, the Fermi Large Area Telescope (LAT) has detected thousands of sources, many of which remain unassociated. Some may be extended sources represented in the catalog by multiple point-like entries. The reinterpretation of HESS J1813-178 as a single extended source motivates a systematic search for further missed extended sources. Aims. We search for clusters of unassociated Fermi-LAT sources and test whether single extended-source models describe them better than multiple catalog sources. Methods. We apply the DBSCAN (Density-Based Spatial Clustering of Applications with Noise) algorithm to 4FGL sources with a linking scale of $\epsilon = 0.3^\circ$ over the 5 GeV to 1 TeV energy range. 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 compare extended- and multiple-source models and characterize each candidate spectrally and morphologically, focusing on the Galactic plane. Results. We identify 48 clusters containing 124 sources, each with at least one unassociated source. For all eight clusters passing our quality selection, an extended-source model is statistically preferred. At linking scales of $0.4^\circ$ and $0.5^\circ$, all eight retain their core sources. Cross-matches with the Second Fermi Galactic Extended Sources Catalog (2FGES) and the HESS Galactic Plane Survey (HGPS) show that five overlap known extended sources. The other three, including one with morphology dependent on the interstellar emission model, have no counterpart in either catalog and are new extended-source candidates. Conclusions. Spatial clustering combined with likelihood-based model comparison can uncover extended sources missed in the Fermi-LAT catalog and complements existing searches.

astro-ph.HE↗

arXiv2026

Search for gamma-ray variability around Fermi-LAT pulsar glitches

Pulsars are the most numerous class of Galactic gamma-ray sources detected by the Fermi Large Area Telescope (LAT). Young pulsars occasionally experience sudden timing discontinuities called glitches, characterized by rapid changes in rotational parameters, usually followed by a return to regular rotation. PSR J2021+4026 is unique among Fermi-LAT pulsars, exhibiting quasiperiodic switches between two states with varying spin-down rates approximately every 3-4 years, correlated with sudden changes in gamma-ray emission features. This study searched for gamma-ray emission variability in pulsars correlated with glitch occurrence. We introduced a novel approach to analyzing LAT gamma-ray pulsars through systematic examination of variability associated with spin-down rate changes. We tracked rotation and gamma-ray emission changes for seven promising glitches selected based on observed spin-down rate variations. Using 14 years of Fermi-LAT data, we conducted binned likelihood spectral analysis of data windows around selected glitch epochs. We improved best-fit parameter precision by incorporating likelihood weights calculated from diffuse background models, accounting for systematic error contributions. The phase-averaged flux and spectral parameters of analyzed pulsars showed no significant variation across investigated glitches. The 95% upper limits on relative flux change indicate the Vela pulsar flux is unchanging, with a 0.5% upper limit on relative change, making it promising for further searches. The connection between glitch dynamics and gamma-ray emission remains unclear, and PSR J2021+4026 remains unique in its gamma-ray variability properties. We conclude that comprehensive investigation of glitches is warranted to further unravel their underlying mechanisms.

astro-ph.HE↗

arXiv2025

Clustering analysis of Fermi-LAT unidentified point sources

The Fermi Large Area Telescope (LAT) has detected thousands of sources since its launch in 2008, with many remaining unidentified. Some of these point sources may arise from source confusion. Specifically, there could be extended sources erroneously described as groups of point sources. Using the DBSCAN clustering algorithm, we analyze unidentified Fermi-LAT sources alongside some classified objects from the 4FGL-DR4 catalog. We identified 44 distinct clusters containing 106 sources, each including at least one unidentified source. Detailed modeling of selected clusters reveals some cases where extended source models are statistically preferred over multiple point sources. The work is motivated by prior observations of extended TeV gamma-ray sources, such as HESS J1813-178, and their GeV counterparts. In the case of HESS J1813-178, two unidentified Fermi-LAT point sources were detected in the region. Subsequent multiwavelength analysis combining TeV and GeV data showed that a single extended source is a better description of the emission in this region than two point-like sources.

astro-ph.HE↗