Timing of Eight Binary Millisecond Pulsars Found with Arecibo in Fermi-LAT Unidentified Sources

TL;DR

This paper reports the discovery and timing of eight binary millisecond pulsars from Fermi-LAT sources using Arecibo, revealing diverse companion types, gamma-ray pulsations, and eclipsing behaviors, and discusses implications for future pulsar searches.

Contribution

First timing solutions for eight binary MSPs discovered via Fermi-LAT sources, including detailed orbital and eclipse characteristics, expanding knowledge of MSP populations and gamma-ray associations.

Findings

All MSPs show gamma-ray pulsations confirmed by Fermi data.

Eclipsing behaviors vary, with redbacks eclipsed 50% of the orbit.

The study suggests potential biases in MSP detection related to orbital periods.

Abstract

We present timing solutions for eight binary millisecond pulsars (MSPs) discovered by searching unidentified Fermi-LAT source positions with the 327 MHz receiver of the Arecibo 305-m radio telescope. Five of the pulsars are "spiders" with orbital periods shorter than 8.1 h. Three of these are in "black widow" systems (with degenerate companions of 0.02-0.03 solar masses), one is in a "redback" system (with a non-degenerate companion of $\gtrsim 0.3$ solar masses), and one (J1908+2105) is an apparent middle-ground case between the two observational classes. The remaining three pulsars have white dwarf companions and longer orbital periods. With the initially derived radio timing solutions, we detected gamma-ray pulsations from all MSPs and extended the timing solutions using photons from the full Fermi mission, thus confirming the identification of these MSPs with the Fermi-LAT sources. The radio emission of the redback is eclipsed during 50% of its orbital period, which is typical for this kind of system. Two of the black widows exhibit radio eclipses lasting for 10-20% of the orbit, while J1908+2105 eclipses for 40% of the orbit. We investigate an apparent link between gamma-ray emission and a short orbital period among known binary MSPs in the Galactic disk, and conclude that selection effects cannot be ruled out as the cause. Based on this analysis we outline how the likelihood of new MSP discoveries can be improved in ongoing and future pulsar searches.