Nearby SN-Associated GRB~190829A: Environment, Jet Structure, and VHE Gamma-Ray Afterglows

Abstract

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 ($A_{\mathrm{V}}=2.33$) 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 $R=(4.07-6.46)\times 10^{16}\mathrm{cm}$, 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).

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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Cited by in corpus (13)

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• Synchrotron Self-Compton Emission in the Two-Component Jet Model for Gamma-Ray Bursts
• Prompt emission and early optical afterglow of VHE detected GRB 201015A and GRB 201216C: onset of the external forward shock
• The origin of very-high-energy gamma-rays from GRB 221009A: implications for reverse shock proton synchrotron emission
• VLBI observations of GRB 201015A, a relatively faint GRB with a hint of Very High Energy gamma-ray emission
• Very-High-Energy Gamma-Ray Afterglows of GRB 201015A and GRB 201216C
• Photometric and Spectroscopic Observations of GRB 210104A: Bright Reverse shock Emission and Dense Circumburst Environment
• Hard TeV Gamma-Ray Afterglows of Nearby GRB 190829A as a Tentative Signature of Ultra-High-Energy Cosmic Rays Accelerated in Gamma-Ray Burst Jets
• Time dependent numerical model for the very high energy emissions of distant gamma-ray busrt GRB 201216C
• Very high-energy gamma rays from GRB 180720B and GRB 190829A with external Compton emission
• Jet-Cocoon Geometry in the Optically Dark, Very High Energy Gamma-ray Burst 201216C