Unveiling the nature of the unidentified gamma-ray sources III: gamma-ray blazar-like counterparts at low radio frequencies

TL;DR

This study uses low-frequency radio surveys to identify potential gamma-ray blazar counterparts among unidentified sources in the Fermi LAT catalog, leading to the discovery of new candidates and highlighting the method's effectiveness.

Contribution

The paper introduces a novel approach combining low-frequency radio data with multiwavelength analysis to identify gamma-ray blazar candidates among previously unidentified sources.

Findings

Identified 23 new gamma-ray blazar candidates.

Linked low-frequency radio properties to gamma-ray source counterparts.

Demonstrated the effectiveness of low-frequency radio surveys in UGS identification.

Abstract

About one third of the gamma-ray sources listed in the second Fermi LAT catalog (2FGL) have no firmly established counterpart at lower energies so being classified as unidentified gamma-ray sources (UGSs). Here we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. Comparison with previous results on the UGSs are also presented. Finally, we speculate on the advantages on the use of the low-frequency radio observations to associate UGSs and to search for gamma-ray pulsar candidates.