Nearly 1/3 of the sources listed in the Third Fermi Large Area Telescope ( LAT ) catalog ( 3FGL ) remain unassociated .
It is possible that predicted and even unanticipated gamma-ray source classes are present in these data waiting to be discovered .
Taking advantage of the excellent spectral capabilities achieved by the Fermi LAT , we use machine learning classifiers ( Random Forest and XGBoost ) to pinpoint potentially novel source classes in the unassociated 3FGL sample outside the Galactic plane .
Here we report a total of 34 high-confidence Galactic candidates at |b| \geq 5 \mathrm { { } ^ { \circ } } .
The currently favored standard astrophysical interpretations for these objects are pulsars or low-luminosity globular clusters hosting millisecond pulsars ( MSPs ) .
Yet , these objects could also be interpreted as dark matter annihilation taking place in ultra-faint dwarf galaxies or dark matter subhalos .
Unfortunately , Fermi LAT spectra are not sufficient to break degeneracies between the different scenarios .
Careful visual inspection of archival optical images reveals no obvious evidence for low-luminosity globular clusters or ultra-faint dwarf galaxies inside the 95 % error ellipses .
If these are pulsars , this would bring the total number of MSPs at |b| \geq 5 \mathrm { { } ^ { \circ } } to 106 , down to an energy flux \approx 4.0 \times 10 ^ { -12 } erg cm ^ { -2 } s ^ { -1 } between 100 MeV and 100 GeV .
We find this number to be in excellent agreement with predictions from a new population synthesis of MSPs that predicts 100–126 high-latitude 3FGL MSPs depending on the choice of high-energy emission model .
If , however , these are dark matter substructures , we can place upper limits on the number of Galactic subhalos surviving today and on dark matter annihilation cross sections .
These limits are beginning to approach the canonical thermal relic cross section for dark matter particle masses below \sim 100 GeV in the bottom quark ( b \bar { b } ) annihilation channel .