TeV Emission from Gamma-Ray Bursts: Signatures of Inverse Compton Scattering Induced by Kilonova-Jet Interactions

The fireball model is widely used to explain the spectral energy distribution and light curves of gamma-ray bursts (GRBs) during the afterglow phase [39]. According to this model, particles are accelerated in external shocks, resulting in photon emission via synchrotron radiation and synchrotron self-Compton (SSC) processes [43, 44]. However, this framework does not fully account for all observed cases. Notably, the GeV excess detected in GRB 211211A has been attributed to external inverse-Compton (EIC) interactions, where optical kilonova photons are upscattered by electrons accelerated in the forward shock of a weaker secondary jet [30]. Observations with the High Altitude Water Cherenkov (HAWC) gamma-ray observatory revealed emission spatially coincident with a few GRBs, detected at timescales consistent with the expected kilonova emission peak. In this work, we argue that the detected VHE photons indeed originate from these GRBs, the SSC mechanism in both forward and reverse shocks fails to account for this emission. Instead, we propose that these photons result from inverse-Compton scattering of kilonova photons by electrons within the reverse shock.