  In a previous paper, we pointed out that the gamma-ray source 3FGL
J2212.5+0703 shows evidence of being spatially extended. If a gamma-ray source
without detectable emission at other wavelengths were unambiguously determined
to be spatially extended, it could not be explained by known astrophysics, and
would constitute a smoking gun for dark matter particles annihilating in a
nearby subhalo. With this prospect in mind, we scrutinize the gamma-ray
emission from this source, finding that it prefers a spatially extended profile
over that of a single point-like source with 5.1 sigma statistical
significance. We also use a large sample of active galactic nuclei and other
known gamma-rays sources as a control group, confirming, as expected, that
statistically significant extension is rare among such objects. We argue that
the most likely (non-dark matter) explanation for this apparent extension is a
pair of bright gamma-ray sources that serendipitously lie very close to each
other, and estimate that there is a chance probability of ~2% that such a pair
would exist somewhere on the sky. In the case of 3FGL J2212.5+0703, a model
with a second gamma-ray point source at the location of a known BZCAT/CRATES
radio source yields fits that are comparable in quality to those obtained for a
single extended source. If 3FGL J2212.5+0703 is a dark matter subhalo, it would
imply that dark matter particles have a mass of ~18-33 GeV and an annihilation
cross section on the order of sigma v ~ 10^-26 cm^3/s (for the representative
case of annihilations to bb), similar to the values required to generate the
Galactic Center gamma-ray excess.

High Energy Astrophysical Phenomena;Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies;High Energy Physics - Phenomenology