Contribution of dark matter annihilation to gamma-ray burst afterglows
  near massive galaxy centers
  Gamma-ray bursts (GRBs) are believed to be powered by ultrarelativistic jets.
If these jets encounter and accelerate excess electrons and positrons produced
by particle dark matter (DM) annihilation, the observed electromagnetic
radiation would be enhanced. In this paper, we study GRB afterglow emission
with the presence of abundant DM under the weakly interacting massive particle
annihilation conditions. We calculate the light curves and spectra of the GRB
afterglows with different parameters, i.e., DM density, particle DM mass,
annihilation channel, and electron density of the interstellar medium. We find
that the effect of DM may become noticeable in the afterglow spectra if the
circumburst has a low electron number density ($n \lesssim 0.1~\rm cm^{-3}$)
and if the DM has a high number density ($\rho_\chi \gtrsim 10^3~\rm
GeV~cm^{-3}$). According to the standard galaxy DM density profile, GRB
afterglows with DM contribution might occur at distances of several to tens of
parsecs from the centers of massive galaxies.
