3FGL J1924.8-1034: A spatially extended stable unidentified GeV source?

Abstract

Milky Way-like galaxies are predicted to host a very large number of dark matter subhalos. Some massive and nearby subhalos could generate detectable gamma-rays, appearing as unidentified, spatially-extended and stable gamma-ray sources. We search for such sources in the third Fermi Large Area Telescope source List (3FGL) and report the identification of a new candidate, 3FGL J1924.8-1034. With the Fermi-LAT Pass 8 data, we find that 3FGL J1924.8-1034 is spatiallyextended at a high confidence level of 5.4σ, with a best-fit extension radius of ∼ 0.15• . No significant variability has been found and its gamma-ray spectrum is well fitted by the dark matter annihilation into bb with a mass of ∼ 43 GeV. All these facts make 3FGL J1924.8-1034 a possible dark matter subhalo candidate. However, due to the limited angular resolution, the possibility of that the spatial extension of 3FGL J1924.8-1034 is caused by the contamination from the other un-resolved point source can not be ruled out.

A Gaia DR2 search for dwarf galaxies towards Fermi-LAT sources: implications for annihilating dark matter

“…Using an analytical model of subhalo mass stripping that has been calibrated against numerical simulation results, combined with current limits on the DM annihilation cross section from known Milky Way dSphs, we estimated the gamma-ray flux and source size as a function of pre-infall halo mass for all eight Fermi-LAT sources. We concluded that our model rejects the possibility of a DM annihilation scenario for the two sources: 3FGL J2212.5+0703 (Bertoni et al 2016) and 3FGL J1924.8-1034 (Xia et al 2017) if the pre-infall DM halo mass is less than M 200 < 10 9 M at distance of d < 20 kpc, as constrained by our work. If the subhalo is farther away than 20 kpc, then its DM halo has to be larger than M 200 = 10 9 M .…”

“…The differences come from the fact that small changes of internal profiles such as r s and ρ s (e.g., Peñarrubia et al 2010) have been taken into account for the former approach based on Bartels & Ando (2015) and Hiroshima et al (2018), but not in the latter. 1034 (circle; Xia et al 2017), the measured signals are incompatible with a DM annihilation interpretation, even for halos at the pre-infall halo mass upper bound of M 200 = 10 9 M . We note that recently Fermi- LAT Collaboration & Biteau (2018) reported that the gamma-ray signals from both 3FGL J2212.5+0703 and 3FGL J1924.8-1034 are better explained by two point sources rather than a single extended source.…”

Unidentified gamma-ray sources as targets for indirect dark matter detection with theFermi-Large Area Telescope

“…We note that no source flagged as extended in the catalogs survived our cuts. In particular, the source 3FGL J2212.5+0703, which is marked as possible DM subhalo by [30], is rejected by its multiwavelength emission, and 3FGL J1924.8-1034, which is also marked as a possible extended DM subhalo by [88], is classified as an AGN by the machine-learning algorithms. Table 2 summarizes the expected efficiency, defined as the fraction of each filtering effect which is univocally applied (i.e., with no possibility of a false positive), and how we dealt in each case with the fact of not having 100% efficiency.…”

Search for line-like signals in the all-sky Fermi-LAT data

“…For some subhalos which are too small to capture enough baryonic matter (i.e., M sub < 10 8 M ), the gamma-ray annihilation signals would be the only channel to observe them. Thus, it is supposed that some unassociated Fermi-LAT sources are potential DM subhalos [28][29][30][31][32][33][34][35][36], especially those spatially extended and with spectra compatible with DM signals [32,35,36].…”