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Durham University

Department of Physics

Staff profile

Publication details for Dr Anthony Brown

Brown, Anthony M., Lacroix, Thomas, Lloyd, Sheridan, Bœhm, Céline & Chadwick, Paula (2019). Reply to “Comment on ‘Understanding the γ -ray emission from the globular cluster 47 Tuc: Evidence for dark matter?”’. Physical Review D 100(6): 068302.

Author(s) from Durham


Analyzing nine years of Fermi-LAT observations, we recently studied the spectral properties of the
prominent globular cluster [Phys. Rev. 98, 041301 (2018)]. In particular, we investigated several models to
explain the observed gamma-ray emission, ranging from millisecond pulsars (MSPs) to dark matter (DM),
with the motivation for the latter model driven by recent evidence that 47 Tuc harbors an intermediate-mass
black hole [B. Kiziltan et al., Nature (London) 542, 203 (2017)]. This investigation found evidence that the
observed gamma-ray emission from 47 Tuc is due to two source populations of MSPs and DM. In
preceding Comment [Phys. Rev. D 100, 068301 (2019)], Bartels and Edwards comment that this evidence
is an artifact of the MSP spectra used in our paper. Here, we reply to this comment and argue that (i) Bartels
and Edwards do not give due consideration to a very important implication of their result and (ii) there is
tension between our MSP fit and their MSP fit when taking uncertainties into consideration. As such, we
still conclude there is evidence for a DM component which motivates a deeper radio study of the prominent
globular cluster 47 Tuc.