On the orbital properties of millisecond pulsar binaries

TL;DR

This paper analyzes the orbital properties of millisecond pulsar binaries with white dwarf companions, revealing new gaps in orbital period distribution and correlations with companion mass, advancing understanding of their evolutionary history.

Contribution

It identifies a new orbital period gap and characterizes subpopulations of MSP binaries, providing insights into their binary evolution and companion mass relations.

Findings

Discovery of a new orbital period gap at 2.5-4.5 days.

Correlation between orbital period and companion mass in different subpopulations.

Distinct evolutionary pathways for MSP binaries with different white dwarf types.

Abstract

We report a detailed analysis of the orbital properties of binary millisecond pulsar (MSP) with a white dwarf (WD) companion. Positive correlations between the orbital period $P_{\rm b}$ and eccentricity $\epsilon$ are found in two classes of MSP binaries with a He WD and with a CO/ONeMg WD, though their trends are different. The distribution of $P_{\rm b}$ is not uniform. Deficiency of sources at $P_{\rm b}\sim35-50$~days (Gap 1) have been mentioned in previous studies. On the other hand, another gap at $P_{\rm b}\sim2.5-4.5$~days (Gap 2) is identified for the first time. Inspection of the relation between $P_{\rm b}$ and the companion masses $M_{\rm c}$ revealed the subpopulations of MSP binaries with a He WD separated by Gap 1, above which $P_{\rm b}$ is independent of $M_{\rm c}$ (horizontal branch) but below which $P_{\rm b}$ correlates strongly with $M_{\rm c}$ (lower branch). Distinctive horizontal branch and lower branch separated by Gap 2 were identified for the MSP binaries with a CO/ONeMg WD at shorter $P_{\rm b}$ and higher $M_{\rm c}$. Generally, $M_{\rm c}$ are higher in the horizontal branch than in the lower branch for the MSP binaries with a He WD. These properties can be explained in terms of a binary orbital evolution scenario in which the WD companion was ablated by a pulsar wind in the post mass-transfer phase.