  We propose that the nearly massless dark photons produced from the
annihilation of keV dark fermions in the Galaxy can induce the excess of
electron recoil events recently observed in the XENON1T experiment. The minimal
model for this is the extension of a $U(1)_{X}$ gauge symmetry, under which the
dark photon couples to both dark and visible matter currents. We find that the
best-fit parameters of the dark sector are compatible with the most stringent
constraints from stellar cooling. We also show that in the freeze-out scenario,
the dark fermions can explain the anomaly while contributing $\gtrsim 1\%$ of
the DM relic density.

High Energy Physics - Phenomenology;High Energy Astrophysical Phenomena