  Several groups have recently claimed evidence for an unaccounted gamma-ray
excess over {the} diffuse backgrounds at few GeV in {the} Fermi-LAT data in a
region around the Galactic Center, consistent with a dark matter annihilation
origin. We demonstrate that the main spectral and angular features of this
excess can be reproduced if they are mostly due to inverse Compton emission
from high-energy electrons injected in a burst event of ~10^52 - 10^53erg
roughly O(10^6) years ago. We consider this example as a proof of principle
that time-dependent phenomena need to be understood and accounted for -
together with detailed diffuse foregrounds and unaccounted "steady state"
astrophysical sources - before any robust inference can be made about dark
matter signals at the Galactic Center. In addition, we point out that the
timescale suggested by our study, which controls both the energy cutoff and the
angular extension of the signal, intriguingly matches (together with the energy
budget) what is indirectly inferred by other evidences suggesting a very active
Galactic Center in the past, for instance related to intense star formation and
accretion phenomena.

High Energy Astrophysical Phenomena;High Energy Physics - Phenomenology