A Search for Millisecond Pulsars in Fermi LAT-Detected Globular Clusters

TL;DR

This study searched for millisecond pulsars in two gamma-ray detected globular clusters, discovering one MSP in NGC 6652, which may explain the clusters' gamma-ray emission and provides insights into pulsar populations.

Contribution

First search for MSPs in these clusters using Green Bank Telescope, discovering a new MSP and analyzing its potential link to gamma-ray emission.

Findings

Discovered one MSP in NGC 6652 within the gamma-ray error circle.

The MSP has a lower dispersion measure than predicted by models.

Uncertain whether the MSP is a cluster member or foreground object.

Abstract

We have searched for millisecond pulsars (MSPs) in two globular clusters detected by the Fermi Large Area Telescope. These clusters contained no known MSPs prior to their detections in gamma rays. The discovery of gamma ray emission from many MSPs and the prevalence of MSPs in globular clusters points to a population of MSPs as the likely source of the detected GeV emission, directing our search for new cluster MSPs. We observed NGC 6652 and NGC 6388 at 2 GHz with the Green Bank Ultimate Pulsar Processing Instrument pulsar backend at the Green Bank Telescope using the coherent dedispersion mode. We have discovered one MSP in the gamma ray error circle of NGC 6652. This pulsar is interesting because, while positionally coincident with the GC, it has a much lower dispersion measure than expected from the NE2001 galactic free electron density model. It is unclear whether the MSP is a foreground pulsar or a cluster member, and whether the pulsar, cluster, or both, is responsible for the gamma ray emission. Timing the MSP will give the pulsar position and a solid identification of the pulsar as a cluster member if it is within a few core radii of the cluster center, as well as the opportunity to search for gamma ray pulsations and determine the origin of the GeV emission.