A Candidate Open Cluster Pulsar: Timing Analysis of PSR J1922+3745 in NGC 6791

TL;DR

This study presents detailed timing analysis of PSR J1922+3745, a potential open cluster pulsar in NGC 6791, but current evidence does not confirm its cluster membership, highlighting the need for further searches.

Contribution

The paper provides the first phase-coherent timing solution and polarization measurements of PSR J1922+3745, and evaluates methods to confirm its association with NGC 6791.

Findings

PSR J1922+3745 is an isolated slow pulsar with a characteristic age of 7.8 Myr.

Deeper searches did not find additional pulsars in NGC 6791.

HI absorption spectroscopy is unlikely to constrain the pulsar's distance with current sensitivity.

Abstract

PSR J1922+3745 was recently identified as a radio pulsar toward the old open cluster NGC 6791, raising the prospect of the first pulsar associated with an open cluster. We report FAST follow-up observations that yield a phase-coherent timing solution, a precise position, a measurement of the spin-down rate and the pulsar's polarization properties. PSR J1922+3745 is consistent with an isolated slow pulsar with a characteristic age of 7.8 Myr, comparable to the small population of long-period pulsars found in globular clusters. Motivated by the potential cluster association, we re-process deeper searches of the NGC 6791 field at higher sensitivity but detect no additional pulsars. We also assess whether HI absorption spectroscopy can provide a useful distance constraint and find that such measurements are unlikely to be constraining with currently available sensitivity. Consequently, existing evidence does not yet establish membership in NGC 6791. Further deep searches for additional pulsars with similar dispersion measures in the cluster field will likely be the most direct path to confirming a physical association.