3FGL J1924.8-1034 : A Spatially-Extended Stable Unidentified GeV Source?
  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
spatially-extended at a high confidence level of $5.4\sigma$, with a best-fit
extension radius of $\sim0.15^{\circ}$. No significant variability has been
found and its gamma-ray spectrum is well fitted by the dark matter annihilation
into $b\bar{b}$ with a mass of $\sim 43$ 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.
