Sheridan J. Lloyd
Gamma-ray emission from high Galactic latitude globular clusters
Lloyd, Sheridan J.; Chadwick, Paula M.; Brown, Anthony M.
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.
Citation
Lloyd, S. J., Chadwick, P. M., & Brown, A. M. (2018). Gamma-ray emission from high Galactic latitude globular clusters. Monthly Notices of the Royal Astronomical Society, 480(4), 4782-4796. https://doi.org/10.1093/mnras/sty2150
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 |
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.
Published Journal Article
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