Search for gamma-ray emission from the 12 nearby dwarf spheroidal galaxies with 12 years of Fermi-LAT data

Abstract

Previously, we have shown in Li et al. (2018) that very weak $\gamma$-ray excesses ($\sim 2\sigma$) appear in some Milky Way dwarf spheroidal galaxies (dSphs, including candidates) and the combination analysis of 12 nearby dSphs yields a local significance of $>4\sigma$. In this work, we adopt a longer data set (i.e., the 12 years of Fermi-LAT data), the latest Fermi-LAT software as well as background models to update the searches of $\gamma$-ray emission from these sources. Very weak $\gamma$-ray excesses ($>$ 2 $\sigma$) are found in the directions of three dSphs, including Reticulum II, Bootes II and Willman 1. In the direction of Reticulum II, the peak TS value of the excess reaches $\sim$11. However, different from the previous analysis with the 9 years of Fermi-LAT data, now the location of the gamma-ray emission is significantly away from the center of Reticulum II because of the enhancement of "offset" $\gamma$-rays above 10 GeV since 2017. The detected weak excess is likely due to the contamination of an astrophysical $\gamma$-ray source with a TS value of $\sim 22$, irrelevant to the dark matter inside Reticulum II. The possible excesses in the directions of Bootes II and Willman 1 are weaker with lower peak TS values ($\sim 7$). If interpreted as annihilation of dark matter particles into ${\tau }^{+}{\tau }^{-}$, the dark mass mass of $m_{\chi }\sim 14$ GeV and $\sim 80$ GeV are found for Bootes II and Willman 1, respectively. Much more data are needed to clarify whether these two potential signals are real and then reveal their origins.

10 pages, 6 figures, accepted for publication in PRD

References in corpus (19)

• Dark Matter Candidates from Particle Physics and Methods of Detection
• Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons
• Searching for Dark Matter Annihilation in Recently Discovered Milky Way Satellites with Fermi-LAT
• Background model systematics for the Fermi GeV excess
• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• Roma-BZCAT: A multifrequency catalogue of Blazars
• Dark Matter and Collider Phenomenology of Universal Extra Dimensions
• The DArk Matter Particle Explorer mission
• CGRaBS: An All-Sky Survey of Gamma-Ray Blazar Candidates
• Dwarf galaxy annihilation and decay emission profiles for dark matter experiments
• GeV excess in the Milky Way: The Role of Diffuse Galactic gamma ray Emission template
• A Comprehensive Search for Dark Matter Annihilation in Dwarf Galaxies
• A New Faint Milky Way Satellite Discovered in the Pan-STARRS1 3 pi Survey
• The WISE Blazar-Like Radio-Loud Sources: An All-Sky Catalog Of Candidate Gamma-Ray Blazars
• A Hero's Dark Horse: Discovery of an Ultra-Faint Milky Way Satellite in Pegasus
• An Ultra-Faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey
• A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey
• Extracting limits on Dark Matter annihilation from gamma-ray observations towards dwarf spheroidal galaxies
• Search for gamma-ray line features from Milky Way satellites with Fermi-LAT Pass 8 data

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