An image-based search for pulsars among Fermi unassociated LAT sources

TL;DR

This paper presents an image-based radio method using compactness and spectral index criteria to identify pulsar candidates among Fermi LAT sources, leading to the discovery of multiple pulsars and expanding the search strategies.

Contribution

The study introduces a novel radio imaging approach for pulsar candidate selection, demonstrating its effectiveness in discovering new pulsars among Fermi unassociated sources.

Findings

Six millisecond pulsars discovered

One normal pulsar discovered

Radio imaging expands pulsar search space

Abstract

We describe an image-based method that uses two radio criteria, compactness and spectral index, to identify promising pulsar candidates among Fermi Large Area Telescope (LAT) unassociated sources. These criteria are applied to those radio sources from the Giant Metrewave Radio Telescope all-sky survey at 150 MHz (TGSS ADR1) found within the error ellipses of unassociated sources from the 3FGL catalog and a preliminary source list based on 7 years of LAT data. After follow-up interferometric observations to identify extended or variable sources, a list of 16 compact, steep-spectrum candidates is generated. An ongoing search for pulsations in these candidates, in gamma rays and radio, has found six millisecond pulsars and one normal pulsar. A comparison of this method with existing selection criteria based on gamma-ray spectral and variability properties suggests that the pulsar discovery space using Fermi may be larger than previously thought. Radio imaging is a hitherto underutilized source selection method that can be used, as with other multi-wavelength techniques, in the search for Fermi pulsars.