External Inverse-Compton Emission From Low-Luminosity Gamma-Ray Bursts: Application To Grb 190829a

The detection of TeV gamma-ray bursts (GRBs) brought new opportunities for studying the physics of particle acceleration at relativistic shocks. The High Energy Stereoscopic System (H.E.S.S.) 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 similar to 10(3) 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 dissipations are upscattered to VHE energies by the nonthermal electrons accelerated at the external forward shock. Our calculations show that the EIC flare nearly coincides with the late-prompt flare, but extends similar to 3-4 times longer than the duration of the late-prompt flare. The preferred kinetic energy and initial Lorentz factor used in our model are similar to 10(52) erg and similar to 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.