Four Highly Dispersed Millisecond Pulsars Discovered in the Arecibo PALFA Galactic Plane Survey

TL;DR

This paper reports the discovery and timing of four highly dispersed millisecond pulsars from the PALFA survey, including three in binary systems and one isolated, highlighting PALFA's effectiveness in detecting distant, faint MSPs.

Contribution

It presents four new MSP discoveries with detailed timing and binary characteristics, expanding the known population and demonstrating PALFA's capability for finding faint, distant pulsars.

Findings

Three pulsars are in low-eccentricity binary systems with white dwarf companions.

All four pulsars have high DM/P ratios among Galactic field MSPs.

These discoveries increase the confirmed MSPs from PALFA to fifteen.

Abstract

We present the discovery and phase-coherent timing of four highly dispersed millisecond pulsars (MSPs) from the Arecibo PALFA Galactic plane survey: PSRs J1844+0115, J1850+0124, J1900+0308, and J1944+2236. Three of the four pulsars are in binary systems with low-mass companions, which are most likely white dwarfs, and which have orbital periods on the order of days. The fourth pulsar is isolated. All four pulsars have large dispersion measures (DM > 100 pc cm-3), are distant (> 3.4 kpc), faint at 1.4 GHz (< 0.2 mJy), and are fully recycled (with spin periods P between 3.5 and 4.9 ms). The three binaries also have very small orbital eccentricities, as expected for tidally circularized, fully recycled systems with low-mass companions. These four pulsars have DM/P ratios that are among the highest values for field MSPs in the Galaxy. These discoveries bring the total number of confirmed MSPs from the PALFA survey to fifteen. The discovery of these MSPs illustrates the power of PALFA for finding weak, distant MSPs at low-Galactic latitudes. This is important for accurate estimates of the Galactic MSP population and for the number of MSPs that the Square Kilometer Array can be expected to detect.