The Detection of Fermi AGN above 100 GeV using Clustering Analysis

TL;DR

This study applies a clustering algorithm to Fermi-LAT data to identify new very high energy gamma-ray sources, discovering 9 new VHE AGN candidates and confirming known sources, thus expanding the catalog of such objects.

Contribution

The paper introduces a novel clustering analysis approach to detect VHE gamma-ray sources in Fermi-LAT data, identifying new AGN candidates not previously cataloged.

Findings

Identified 9 new VHE AGN sources.

Confirmed 2 previously known Fermi VHE AGN.

Suggested these sources are similar to ground-based VHE AGN populations.

Abstract

The density-based clustering algorithm DBSCAN has been applied to the Fermi Large Area Telescope (LAT) dataset of $ E_{\gamma} \geqslant 100$ GeV events with $\lvert b\rvert>10^{\circ}$, in order to search for new very high energy (VHE) $\gamma$-ray sources. The clustering analysis returned 49 clusters, of which 21 correspond to already known VHE-emitting active galactic nuclei (AGN) within the TeVCat catalogue and a further 11 were found to be significant in a full Fermi analysis. Of these, 2 are previously detected Fermi VHE AGN, and 9 represent new VHE sources consisting of 6 BL Lac objects, one blazar of unknown type and 2 unassociated sources. Comparing these, along with the VHE AGN RBS 0679 and RBS 0970 previously detected with Fermi-LAT, to the current populations of AGN detected with ground-based instruments and Fermi suggests that the VHE-emitting AGN discovered in this study are very similar to the TeVCat AGN and therefore further observations with ground-based imaging atmospheric Cherenkov telescopes are recommended.