A Global Analysis of Dark Matter Signals from 27 Dwarf Spheroidal Galaxies using Ten Years of Fermi-LAT Observations. (arXiv:1812.06986v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hoof_S/0/1/0/all/0/1">Sebastian Hoof</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Geringer_Sameth_A/0/1/0/all/0/1">Alex Geringer-Sameth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Trotta_R/0/1/0/all/0/1">Roberto Trotta</a>
We perform a search for a dark matter signal in Fermi-LAT gamma-ray data from
27 Milky Way dwarf spheroidal galaxies with spectroscopically measured
$J$-factors. Our analysis properly includes uncertainties in $J$-factors and
background normalisations and systematically 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 accurately
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 the $tau^+tau^-$ and $bbar{b}$ channels. We
present new stringent Bayesian and frequentist upper limits on the
velocity-averaged annihilation cross section as a function of the dark matter
mass. The best-fit dark matter parameters associated with the Galactic Centre
excess are excluded at more than 95% confidence level/posterior probability in
the frequentist/Bayesian framework. 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.
We perform a search for a dark matter signal in Fermi-LAT gamma-ray data from
27 Milky Way dwarf spheroidal galaxies with spectroscopically measured
$J$-factors. Our analysis properly includes uncertainties in $J$-factors and
background normalisations and systematically 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 accurately
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 the $tau^+tau^-$ and $bbar{b}$ channels. We
present new stringent Bayesian and frequentist upper limits on the
velocity-averaged annihilation cross section as a function of the dark matter
mass. The best-fit dark matter parameters associated with the Galactic Centre
excess are excluded at more than 95% confidence level/posterior probability in
the frequentist/Bayesian framework. 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.
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