  Fermi-LAT unidentified sources (unIDs) have proven to be compelling targets
for performing indirect dark matter (DM) searches. In a previous work, we found
that among the 1235 unIDs in Fermi-LAT catalogs (3FGL, 2FHL and 3FHL) only 44
of those are DM subhalos candidates. We now implement a spectral analysis to
test whether these remaining sources are compatible or not with DM origin. This
analysis is executed using almost 10 years of Pass 8 Fermi-LAT data. None of
the unIDs are found to significantly prefer DM-induced emission compared to
other, more conventional, astrophysical sources. In order to discriminate
between pulsar and DM sources, we developed a new method which is based on the
source's spectral curvature, peak energy, and its detection significance. We
also look for spatial extension, which may be a hint for a DM origin according
to our N-body simulation studies of the subhalo population. In addition, we
used Gaia DR2 data to search for a potential stellar counterpart to our best DM
subhalo candidates and, although no firm associations could be found, one of
them coincides with the Sagittarius stream. Finally, previous constraints on
the DM annihilation cross section are updated with the new number of remaining
DM subhalo candidates among unIDs. Our limits now rule out canonical thermal
WIMPs up to masses of 10 GeV for $b\bar{b}$ and 20 GeV for $\tau^+\tau^-$
annihilation channels, in this way being as sensitive and complementary to
those obtained from other targets and probes.
