H.E.S.S. upper limit on the very high energy gamma-ray emission from the globular cluster 47 Tucanae

TL;DR

This paper reports H.E.S.S. telescope observations of globular cluster 47 Tucanae, setting upper limits on very high energy gamma-ray emission and constraining models of millisecond pulsar emissions.

Contribution

It provides the first upper limit on VHE gamma-ray flux from 47 Tucanae and constrains pulsar emission models based on these observations.

Findings

Upper limit of 6.7e-13 / cm^2 s for gamma-ray flux above 800 GeV

Constraints on magnetic field strength in pulsar nebulae

Limits on efficiency of spin-down power conversion to gamma-rays

Abstract

Observations of the globular cluster 47 Tucanae (NGC 104), which contains at least 23 millisecond pulsars, were performed with the H.E.S.S. telescope system. The observations lead to an upper limit of F(E>800 GeV) < 6.7e-13 / cm^2 s on the integral gamma-ray photon flux from 47 Tucanae. Considering millisecond pulsars as the unique potential source of gamma-rays in the globular cluster, constraints based on emission models are derived: on the magnetic field in the average pulsar nebula and on the conversion efficiency of spin-down power to gamma-ray photons or to relativistic leptons.