Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 2, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1475-7516/2020/02/012
Keywords
dwarfs galaxies; gamma ray experiments
Funding
- Imperial College President's Scholarship
- Alexander von Humboldt Foundation
- German Federal Ministry of Education and Research
- Science and Technology Facilities Council (U.K.) [ST/N000838/1]
- Fermi Guest Investigator grant [NNX16AR33G]
- Marie Sklodowska-Curie RISE Grant by the European Commission [H2020-MSCA-RISE-2015-691164]
- EPSRC [EP/P020194/1]
- Imperial College Research Computing Service
- National Aeronautics and Space Administration
- Department of Energy in the United States
- Commissariata l'Energie Atomique
- Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France
- Agenzia Spaziale Italiana
- Istituto Nazionale di Fisica Nucleare in Italy
- Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- High Energy Accelerator Research Organization (KEK)
- Japan Aerospace Exploration Agency (JAXA) in Japan
- K. A. Wallenberg Foundation
- Swedish Research Council
- Swedish National Space Board in Sweden
- DOE [DE-AC02-76SF00515]
- EPSRC [EP/P020194/1] Funding Source: UKRI
- STFC [ST/N000838/1, ST/P000762/1] Funding Source: UKRI
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We search for a dark matter signal in 11 years of Fermi-LAT gamma-ray data from 27 Milky Way dwarf spheroidal galaxies with spectroscopically measured J-factors. Our analysis includes uncertainties in J-factors and background normalisations and compares results from a Bayesian and a frequentist perspective. We revisit the dwarf spheroidal galaxy Reticulum II, confirming that the purported gamma-ray excess seen in Pass 7 data is much weaker in Pass 8, independently of the statistical approach adopted. We introduce for the first time posterior predictive distributions to quantify the probability of a dark matter detection from another dwarf galaxy given a tentative excess. A global analysis including all 27 dwarfs shows no indication for a signal in nine annihilation channels. We present stringent new Bayesian and frequentist upper limits on the dark matter cross section as a function of dark matter mass. The best-fit dark matter parameters associated with the Galactic Centre excess are excluded by at least 95% confidence level/posterior probability in the frequentist/Bayesian framework in all cases. However, from a Bayesian model comparison perspective, dark matter annihilation within the dwarfs is not strongly disfavoured compared to a background-only model. These results constitute the highest exposure analysis on the most complete sample of dwarfs to date. Posterior samples and likelihood maps from this study are publicly available.
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