A gamma-ray periodic modulation in Globular Cluster 47 Tucanae
Abstract
The Globular Cluster 47 Tucanae was firstly detected in gamma-rays by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope, and the gamma-ray emission has been widely attributed to the millisecond pulsars. In this work, we analyze the Fermi-LAT pass 8 data ranging from 2008 August to 2017 May and report the detection of a modulation with a period of 18.4160.008 hours at a significance level of 4.8σ. This is the first time to detect a significant modulation with a period much longer than that of millisecond pulsars in gamma-rays from Globular Clusters. The periodic modulation signal appears in the Swift-BAT data as well. The phase-folded Chandra X-ray light curve of a point source may have provided an additional clue.
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