  G31.9+0.0 (3C 391) is a Galactic mixed-morphology supernova remnant observed
in GeV gamma rays by Fermi Gamma Ray Space Telescope's LAT (Fermi-LAT), as well
as in the 0.3-10 keV X-ray band by Suzaku. In this paper, we will present the
analysis results of X- and gamma-ray data of 3C 391 taken with Suzaku and
Fermi-LAT. The X-ray spectrum of 3C 391 was fitted to a single-temperature
variable abundance non-equilibrium ionization model with an electron
temperature of kTe ~ 0.57 keV, an absorbing column density of NH ~ 3.1 x
10^{22} cm^{-2} and a very high ionization age (\tau > 10^{12} cm^{-3} s),
which suggest that the plasma has reached ionization equilibrium. The spectrum
shows clearly detected emission lines of Mg, Si, and S. 3C 391 was detected in
GeV gamma rays with a significance of ~ 13 sigma. The spectrum was fitted with
a log-parabola function, where the spectral index and beta parameters were
found to be \alpha = 2.35 +- 0.07 and \beta = 0.366 +- 0.339. The integrated
flux above 200 MeV was found as F = (2.34 +- 0.37) x 10^{-8} ph cm^{-2} s^{-1}.
These results are in agreement with the Fermi-LAT results given in the 2nd
Fermi-LAT catalog.
