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

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.

💡 Research Summary

The paper reports on deep observations of the globular cluster 47 Tucanae (NGC 104) with the High Energy Stereoscopic System (H.E.S.S.) in order to search for very‑high‑energy (VHE) gamma‑ray emission associated with its known population of at least 23 millisecond pulsars (MSPs). Over a total of roughly 28 hours of good quality data collected between 2004 and 2009, the standard H.E.S.S. analysis chain—image‑parameter cleaning, stereoscopic reconstruction, and background estimation using reflected‑region techniques—was applied. No statistically significant excess was found above an analysis threshold of 800 GeV. Consequently, a 99 % confidence‑level upper limit on the integral photon flux was derived:

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