Pulsar Candidates Toward Fermi Unassociated Sources

TL;DR

This study searches for steep spectrum radio sources within Fermi unassociated sources, identifying pulsar candidates that may have been missed by previous surveys due to interstellar effects or binary motion.

Contribution

It introduces a method to identify pulsar candidates based on steep spectrum radio sources using existing catalogs and new low-frequency survey data.

Findings

Identified 11 Fermi sources with point-like, steep spectrum radio candidates.

Suggests many candidates could be undiscovered pulsars hidden by interstellar effects.

Proposes targeted gamma-ray and radio searches to confirm pulsations.

Abstract

We report on a search for steep spectrum radio sources within the 95% confidence error ellipses of the Fermi unassociated sources from the Large Array Telescope (LAT). Using existing catalogs and the newly released GMRT all-sky survey at 150 MHz we identify compact radio sources that are bright at MHz frequencies but faint or absent at GHz frequencies. Such steep spectrum radio sources are rare and constitute a sample of pulsar candidates, selected independently of period, dispersion measure, interstellar scattering and orbital parameters. We find point-like, steep spectrum candidates toward 11 Fermi sources. Based on the gamma-ray/radio positional coincidence, the rarity of such radio sources, and the properties of the 3FGL sources themselves, we argue that many of these sources could be pulsars. They may have been missed by previous radio periodicity searches due to interstellar propagation effects or because they lie in an unusually tight binary. If this hypothesis is correct, then renewed gamma-ray and radio periodicity searches at the positions of the steep spectrum radio sources may reveal pulsations.