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Several groups have recently claimed evidence for an unaccounted gamma-rayexcess over {the} diffuse backgrounds at few GeV in {the} Fermi-LAT data in aregion around the Galactic Center, consistent with a dark matter annihilationorigin. We demonstrate that the main spectral and angular features of thisexcess can be reproduced if they are mostly due to inverse Compton emissionfrom high-energy electrons injected in a burst event of ~10^52 - 10^53ergroughly O(10^6) years ago. We consider this example as a proof of principlethat 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 darkmatter signals at the Galactic Center. In addition, we point out that thetimescale suggested by our study, which controls both the energy cutoff and theangular extension of the signal, intriguingly matches (together with the energybudget) what is indirectly inferred by other evidences suggesting a very activeGalactic Center in the past, for instance related to intense star formation andaccretion phenomena.

Galactic Center gamma-ray "excess" from an active past of the Galactic Centre?