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arXiv · 1503.02320

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

Alex Geringer-Sameth·Matthew G. Walker·Savvas M. Koushiappas·Sergey E. Koposov·Vasily Belokurov·Gabriel Torrealba·N. Wyn Evans
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Abstract

We present a search for gamma-ray emission from the direction of the newly discovered dwarf galaxy Reticulum II. Using Fermi-LAT 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 x 10^2 GeV. Modeling the background as a Poisson process based on Fermi-LAT diffuse models, and taking into account trials factors, we detect emission with p-value less than 9.8 x 10^-5 (>3.7 sigma). An alternative, model-independent treatment of background reduces the significance, raising the p-value to 9.7 x 10^-3 (2.3 sigma). Even in this case, however, Reticulum II has the most significant gamma-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.

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Alex Geringer-Sameth, Matthew G. Walker, Savvas M. Koushiappas, Sergey E. Koposov, Vasily Belokurov, Gabriel Torrealba, N. Wyn Evans. 2015-07-13. Indication of Gamma-ray Emission from the Newly Discovered Dwarf Galaxy Reticulum II. https://doi.org/10.1103/physrevlett.115.081101

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