http://arxiv.org/abs/2106.03466
We present a self-consistent paradigm for interpreting 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 ($E_p= 624_{-303}^{+2432}$ keV) of its initial pulse with the dusty medium ($A_{\rm V}=2.33$) does not only result in the second soft gamma-ray pulse ($E_p\sim 12$ keV), but also makes a pre-accelerated $e^{\pm}$-rich medium shell via the $\gamma\gamma$ annihilation.In this paradigm, we show that the observed radio, optical, and X-ray afterglow lightcurves are well fit with the forward shock model. Its jet is almost isotropic ($\theta_j>1.0$ rad) with a Lorentz factor of $\sim 35$, and the electron density of the $e^{\pm}$-rich medium shell is $\sim 15$ cm$^{-3}$, about 7~times higher than the electron density of its normal surrounding medium. The GRB ejecta catches up with and propagates into the $e^{\pm}$-rich medium shell at a region of $R=(4.07-6.46)\times 10^{16}~\rm cm$, resulting in a bright afterglow bump at $\sim 10^3$ seconds post 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 (Cherenkov Telescope Arrays).
Z. Lu-Lu, R. Jia, H. Xiao-Li, et. al.
Tue, 8 Jun 21
80/86
Comments: 14 pages, 4 figures, 1 tables; the original version was submitted to ApJ on Feb. 20, 2021 and currently is under review. The H.E.S.S. data published in Science 372, 1081 (2021) are added in the current posted version
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