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We present a self-consistent paradigm to interpret the striking features of nearby low-luminosity GRB 190829A. Its prompt gamma-ray lightcurve has two separated pulses. We propose that the interaction of the hard prompt gamma-ray photons (keV) of its initial pulse with the dusty medium (AV = 2.33) not only results in the second soft gamma-ray pulse (Ep ∼ 12 keV) but also makes a pre-accelerated e± -rich medium shell via the γγ annihilation. In this paradigm, we show that the observed radio, optical, and X-ray afterglow lightcurves are well-fitted with the forward shock model. Its jet is almost isotropic (θj > 1.0 rad) with a Lorentz factor of ∼35, and the electron density of the e± -rich medium shell is ∼15 cm−3, which is about seven times higher than the electron density of its normal surrounding medium. The GRB ejecta catches up with and propagates into the e± -rich medium shell at a region of R = (4.07–6.46) × 1016 cm. This results in a bright afterglow bump at ∼103 seconds after the GRB trigger. The predicted very high energy (VHE) gamma-ray emission from the synchrotron self-Compton process agrees with the H.E.S.S. observation. The derived broadband spectral energy distribution shows that GRB 190829A like nearby GRBs would be promising targets of the VHE gamma-ray telescopes, such as H.E.S.S., MAGIC, and CTA (Cerenkov Telescope Arrays). [ABSTRACT FROM AUTHOR]

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 () and if the DM has a high number density (). 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. [ABSTRACT FROM AUTHOR]