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Understanding the γ-ray emission from the globular cluster 47 Tuc : evidence for dark matter?

Brown, Anthony M. and Lacroix, Thomas and Lloyd, Sheridan and Bœhm, Céline and Chadwick, Paula (2018) 'Understanding the γ-ray emission from the globular cluster 47 Tuc : evidence for dark matter?', Physical review D., 98 (4). 041301(R).


47 Tuc was the first globular cluster observed to be γ -ray bright, with the γ rays being attributed to a population of unresolved millisecond pulsars (MSPs). Recent kinematic data combined with detailed simulations appear to be consistent with the presence of an intermediate mass black hole (IMBH) at the center of 47 Tuc. We analyze nine years of Fermi-LAT observations to study the spectral properties of 47 Tuc with unprecedented accuracy and sensitivity. This nine-year γ -ray spectrum shows that 47 Tuc’s γ -ray flux cannot be explained by MSPs alone due to a systematic discrepancy between the predicted and observed flux. Rather, we find a significant preference ( TS = 40 ) for describing 47 Tuc’s spectrum with a two source population model consisting of an ensemble of MSPs and annihilating dark matter (DM) with an enhanced density around the IMBH when compared to a MSP-only explanation. The best-fit DM mass of 34 GeV is essentially the same as the best-fit DM explanation for the Galactic center “excess” when assuming DM annihilation into b ¯ b quarks. Our work constitutes the first possible evidence of dark matter within a globular cluster.

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Publisher statement:Reprinted with permission from the American Physical Society: Brown, Anthony M., Lacroix, Thomas, Lloyd, Sheridan, Bœhm, Céline & Chadwick, Paula (2018). Understanding the γ-ray emission from the globular cluster 47 Tuc: Evidence for dark matter? Physical Review D 98(4): 041301(R). © (2018) by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:01 June 2018
Date deposited:08 August 2018
Date of first online publication:03 August 2018
Date first made open access:08 August 2018

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