HESS upper limit on the very high energy γ-ray emission from the globular cluster 47 Tucanae

Abstract

Observations of the globular cluster 47 Tucanae (NGC 104), which contains at least 23 ms pulsars, were performed with the HESS telescope system. The observations lead to an upper limit of F(E < 800 GeV) < 6.7 × 10-13 cm-2 s-1 on the integral γ-ray photon flux from 47 Tucanae. Considering millisecond pulsars as the unique potential source of γ-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 γ-ray photons or to relativistic leptons. © 2009 ESO.