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Gamma-ray emission from high Galactic latitude globular clusters

Lloyd, Sheridan J.; Chadwick, Paula M.; Brown, Anthony M.

Gamma-ray emission from high Galactic latitude globular clusters Thumbnail


Authors

Sheridan J. Lloyd

Anthony M. Brown



Abstract

We analyse 8 years of PASS 8 Fermi-LAT data, in the 60 MeV - 300 GeV energy range, from 30 high Galactic latitude globular clusters. Six of these globular clusters are detected with a TS > 25, with NGC 6254 being detected as gamma-ray bright for the first time. The most significant detection is of the well-known globular cluster 47 Tuc, and we produce a refined spectral fit for this object with a log parabola model. NGC 6093, NGC 6752 and NGC 6254 are fitted with hard, flat power law models, NGC 7078 is best fitted with a soft power law and NGC 6218 is best fitted with a hard, broken power law. This variety of spectral models suggests that there is a variety of γ-ray source types within globular clusters, in addition to the traditional millisecond pulsar interpretation. We identify a correspondence between diffuse X-ray emission in globular cluster cores and gamma-ray emission. This connection suggests that gamma-ray emission in globular clusters could also arise from unresolved X-ray sources or a relativistic electron population, perhaps generated by the millisecond pulsars. X-ray observations of further gamma-ray bright globular clusters would allow a functional relationship to be determined between diffuse X-ray and gamma-ray emission.

Journal Article Type Article
Acceptance Date Aug 6, 2018
Online Publication Date Aug 9, 2018
Publication Date Nov 11, 2018
Deposit Date Aug 15, 2018
Publicly Available Date Aug 22, 2018
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 480
Issue 4
Pages 4782-4796
DOI https://doi.org/10.1093/mnras/sty2150
Public URL https://durham-repository.worktribe.com/output/1322918
Related Public URLs https://arxiv.org/abs/1808.03792

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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