Searching for Gamma-Ray Millisecond Pulsars: Selection of Candidates Revisited

Xuejie Dai,Jithesh Vadakkumthani,Zhongxiang Wang

doi:10.3390/galaxies7010031

Abstract

We are starting a project to find γ -ray millisecond pulsars (MSPs) among the unidentified sources detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope (Fermi), by radio observations. The selection of good candidates from analysis of the LAT data is an important part of the project. Given that there is more than 10 years worth of LAT data and the advent of the newly released LAT 8-year point source list (FL8Y), we have conducted a selection analysis, on the basis of our previous analysis, and report the results here. Setting the requirements for the unidentified sources in FL8Y of Galactic latitudes | b | > 5 ∘ and curvature significances >3 σ , there are 202 sources with detection signficances >6 σ . We select 57 relatively bright ones (detection significances >15 σ ) and analyze their 10.2 years of LAT data. Their variability is checked to exclude variable sources (likely blazars), test statistic maps are constructed to avoid contaminated sources, and curvature significances are re-obtained and compared to their γ -ray spectra to exclude non-significant sources. In the end, 48 candidates are found. Based on the available information, mostly from multi-wavelength studies, we discuss the possible nature of several of the candidates. Most of these candidates are currently being observed with the 65-meter Shanghai Tian Ma Radio Telescope.

Highlights

The Large Area Telescope (LAT), onboard the Fermi Gamma-Ray Space Telescope (Fermi), has been monitoring the whole sky for more than 10 years
Among 131 young γ-ray pulsars, only 19 have magnitudes of Galactic latitudes greater than 5◦ ; there is only small chance that we selected candidate young pulsars
Based on the latest FL8Y catalog and analysis of 10.2 years of Fermi LAT data, we have revisited our selection of candidate millisecond pulsars (MSPs)

Summary

Introduction

The Large Area Telescope (LAT), onboard the Fermi Gamma-Ray Space Telescope (Fermi), has been monitoring the whole sky for more than 10 years. Among 131 young (i.e., non-MSP) γ-ray pulsars, only 19 have magnitudes of Galactic latitudes greater than 5◦ ; there is only small chance that we selected candidate young pulsars The latter two help to distinguish a candidate from blazars. Generally described with a power law with an exponential cutoff (i.e., some degree of curvature in the spectra), in contrast to the highly variable and power-law like emission from blazars (e.g., see [1,6]) Using these criteria, we selected 101 sources from 3FGL and found 52 candidate MSPs; 49 were rejected, due to low detection significances (average_sig < 6σ; [3]), confusion or mixed with extended bright emission regions, based on the Test Statistic (TS) maps we calculated [4], or low curvature significances based on spectra we obtained [4,5]. Mainly focused on analysis of the data for the 20 new sources

LAT Data

Variability Analysis

Maximum Likelihood Analysis

Spectral Analysis

Swift X-ray Data Analysis

Results and Discussion