Examining The Fermi-LAT Third Source Catalog in search of dark matter subhalos

Abstract

Dark matter annihilations taking place in nearby subhalos could appear as gamma-ray sources without detectable counterparts at other wavelengths. In this study, we consider the collection of unassociated gamma-ray sources reported by the Fermi Collaboration in an effort to identify the most promising dark matter subhalo candidates. While we identify 24 bright, high-latitude, non-variable sources with spectra that are consistent with being generated by the annihilations of ∼ 20-70 GeV dark matter particles (assuming annihilations to bb), it is not possible at this time to distinguish these sources from radio-faint gamma-ray pulsars. Deeper multi-wavelength observations will be essential to clarify the nature of these sources. It is notable that we do not find any such sources that are well fit by dark matter particles heavier than ∼100 GeV. We also study the angular distribution of the gamma-rays from this set of subhalo candidates, and find that the source 3FGL J2212.5+0703 prefers a spatially extended profile (of width ∼ 0.15 • ) over that of a point source, with a significance of 4.2σ (3.6σ after trials factor).Although not yet definitive, this bright and high-latitude gammaray source is well fit as a nearby subhalo of mχ 20-50 GeV dark matter particles (annihilating to bb) and merits further multi-wavelength investigation. Based on the subhalo distribution predicted by numerical simulations, we derive constraints on the dark matter annihilation cross section that are competitive to those resulting from gamma-ray observations of dwarf spheroidal galaxies, the Galactic Center, and the extragalactic gamma-ray background. PACS numbers: 95.35.+d, 95.95.Pw, 07.85.-m, FERMILAB-PUB-15-124-A arXiv:1504.02087v1 [astro-ph.HE] 8 Apr 2015

Testing the dark matter subhalo hypothesis of the gamma-ray source 3FGL J2212.5+0703

“…For such a purpose, in this work we re-analyze the spatial, temporal and spectral characters of 3FGL J2212.5+0703. The difference between this work and [48,56] are the following: (1) In order to effectively suppress the possible contamination from two nearby extremelybright blazars (3FGL J2254.0+1608 and 3FGL J2232.5+1143), we just take into account the front-converting gammarays that have angular resolutions better than the back-converting photons; (2) We have extended the spectrum analysis down to the energy ∼ 100 MeV and special attention has been given to the possible improvement in the fit by introducing a phenomenological shape in comparison to the bb model. Note that if significant improvement is found, the astrophysical origin will be favored; (3) The variability of the emission in the past 8 years rather than just the first four years has been thoroughly examined to better test the stability.…”

“…3FGL J2212.5+0703 appears elliptical in TS map, and the residual in the left pannel of Fig.1 is caused by the incorrect spatial template. Following [48], to quantify the spatial extension we use a series of 2-D Gaussian distributions with different widths σ as spatial templates. Based on the optimized model in the previous subsection, we change the spatial template and perform optimizations.…”

“…DM subhalos, either massive enough or close enough to the Earth, could be visible in the gamma-ray band [42,43]. More specifically, if 40 GeV DM particles annihilate with a cross section near the latest upper limit, Fermi-LAT might have recorded ∼ 10 DM subhalos [44][45][46][47][48][49]. Due to the short of stars and gas, DM subhalos may be only detectable in gamma-rays and hence are members of the unidentified gamma-ray sources.…”

“…Dedicated efforts have been made to search for such objects [46][47][48][49][50][51][52][53][54][55][56][57][58]. For instance, by fitting spectral energy distribution (SED) with DM spectra, bright high latitude point sources are investigated in [46][47][48][49]56]. Candidates are selected from the spectrally hard sources and their multi-wavelength counterparts are examined in [51,54].…”

“…Machine learning algorithms are also used to classify un-associated sources, and outliers, which are probably DM subhalos, are selected [50,53,57]. One very attractive finding is the identification of a spatially-extended source, 3FGL J2212.5+0703, among the unidentified sources [48,56] in the Fermi-LAT third source catalog (3FGL). In astrophysical scenarios it is rather hard to give rise to a spatially-extended steady source without any association in other wavelength.…”