Searching for radio pulsars in old open clusters from the Parkes archive

TL;DR

This study searched for radio pulsars in old open clusters using archival Parkes data, discovering known pulsars, RRAT candidates, and potential cluster members, highlighting the need for follow-up observations.

Contribution

The paper presents the first systematic search for radio pulsars in old open clusters using archival data, identifying new RRAT candidates and potential cluster-associated neutron stars.

Findings

Identified five known pulsars and three RRAT candidates.

Most detected sources are likely background pulsars based on DM comparison.

Two RRATs have DMs close to cluster values, suggesting possible membership.

Abstract

Motivated by the discovery of a pulsar in the direction of the old open cluster NGC 6791, we conducted a search for radio pulsars in archival Parkes observations targeting similar old open clusters. We reprocessed 224 observations totalling 75.02 hours from four clusters: Theia 1661, NGC 6259, Pismis 3, and Trumpler 20. Our analysis identified five known pulsars and three new rotating radio transient (RRAT) candidates. By comparing the measured dispersion measures (DMs) with the expected DM values for each cluster derived from YMW16 and NE2001 models, we conclude that most detected sources are likely background pulsars. However, RRAT J1749-25 in Theia 1661 and RRAT J1237-60 in Trumpler 20 have DMs reasonably close to their respective clusters, suggesting possible membership. The association between PSR J1750-2536 and Theia 1661 remains ambiguous due to its intermediate DM. These candidate cluster-associated neutron stars warrant follow-up with more sensitive telescopes such as MeerKAT or the SKA, potentially offering valuable insights into neutron star retention mechanisms and evolution in open cluster environments.