Gamma-ray emission from high Galactic latitude globular clusters

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

doi:10.1093/mnras/sty2150

Gamma-ray emission from high Galactic latitude globular clusters

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

Authors

Sheridan J. Lloyd

Professor Paula Chadwick p.m.chadwick@durham.ac.uk
Head Of Department

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.

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.