Detection of High-Energy Gamma-Ray Emission from the Globular Cluster 47 Tucanae with Fermi

TL;DR

This paper reports the first detection of gamma-ray emission from the globular cluster 47 Tucanae using Fermi, attributing the emission to a population of millisecond pulsars and estimating their number.

Contribution

It provides the first gamma-ray detection of a Galactic globular cluster and links the emission to millisecond pulsars, estimating their population within 47 Tucanae.

Findings

Gamma-ray emission detected from 47 Tucanae.

Emission consistent with millisecond pulsar population.

Estimated up to 60 millisecond pulsars in the cluster.

Abstract

Globular clusters are known to harbour a significant population of neutron star X-ray binaries that could be responsible for delaying the inevitable core collapse of these dense clusters. As a result, their progeny, namely millisecond pulsars, are also present in large numbers. Following the confirmation using the Fermi Gamma-ray Space Telescope that millisecond pulsars are indeed gamma-ray emitters, we report on the detection of the Galactic globular cluster 47 Tuc with the Fermi Large Area Telescope. This is the first detection of a Galactic globular cluster in the gamma-ray domain. The gamma-ray spectrum is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.