Indication of Gamma-Ray Emission from the Newly Discovered Dwarf Galaxy Reticulum II

We present a search for γ-ray emission from the direction of the newly discovered dwarf galaxy Reticulum II. Using Fermi-LAT Collaboration data, we detect a signal that exceeds expected backgrounds between ∼2-10  GeV and is consistent with annihilation of dark matter for particle masses less than a...

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Bibliographic Details
Published in:Physical review letters 2015-08, Vol.115 (8), p.081101-081101, Article 081101
Main Authors: Geringer-Sameth, Alex, Walker, Matthew G, Koushiappas, Savvas M, Koposov, Sergey E, Belokurov, Vasily, Torrealba, Gabriel, Evans, N Wyn
Format: Article
Language:English
Subjects:
Cooperation
Cross sections
Dark matter
Diffusion
Dwarf galaxies
Emission
Halos
Particle mass
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Summary:We present a search for γ-ray emission from the direction of the newly discovered dwarf galaxy Reticulum II. Using Fermi-LAT Collaboration data, we detect a signal that exceeds expected backgrounds between ∼2-10  GeV and is consistent with annihilation of dark matter for particle masses less than a few ×10^{2}  GeV. Modeling the background as a Poisson process based on Fermi-LAT diffuse models, and taking into account trial factors, we detect emission with p value less than 9.8×10^{-5} (>3.7σ). An alternative, model-independent treatment of the background reduces the significance, raising the p value to 9.7×10^{-3} (2.3σ). Even in this case, however, Reticulum II has the most significant γ-ray signal of any known dwarf galaxy. If Reticulum II has a dark-matter halo that is similar to those inferred for other nearby dwarfs, the signal is consistent with the s-wave relic abundance cross section for annihilation.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.115.081101