External Inverse-Compton Emission from Low-Luminosity Gamma-Ray Bursts: Application to GRB 190829A

TL;DR

This paper explains the very-high-energy gamma-ray emission observed from a low-luminosity gamma-ray burst, GRB 190829A, using an external inverse-Compton model involving seed photons from late-time flares.

Contribution

The study demonstrates that VHE emission in GRB 190829A can be explained by EIC scattering, providing insights into particle acceleration and central engine activity in low-luminosity GRBs.

Findings

VHE emission is produced by external inverse-Compton scattering of flare photons.

EIC flare duration extends 3-4 times longer than the late-prompt flare.

Model parameters include kinetic energy ~10^{52} erg and Lorentz factor ~20.

Abstract

The detection of TeV gamma-ray bursts (GRBs) brought new opportunities for studying the physics of particle acceleration at relativistic shocks. The \hess telescopes recently observed very-high-energy (VHE) emission from a nearby low-luminosity GRB, GRB 190829A. Follow-up observations with, e.g., Swift-XRT, revealed unusual flare activities at $\sim 10^3\rm~s$, which can be caused by a long-lasting central engine. We show that the VHE emission during the H.E.S.S. observation time is naturally produced in the external inverse-Compton (EIC) scenario, where seed photons supplied by the flares or other late-time dissipation are upscattered to VHE energies by the non-thermal electrons accelerated at the external forward shock. Our calculations show that the EIC flare nearly coincides with the late-prompt flare, but extends $\sim3-4$ times longer than the duration of the late-prompt flare. The preferred kinetic energy and initial Lorentz factor used in our model are $\sim 10^{52}\rm~erg$ and $\sim 20$, respectively. Understanding the mechanisms of the VHE emission from low-luminosity GRBs will help us constrain the properties of the outflow and the central engine activities, as well as the particle acceleration mechanism.