Off-axis jet scenario for early afterglow emission of low-luminosity gamma-ray burst GRB 190829A

ABSTRACT Recently, ground-based Imaging Atmospheric Cherenkov Telescopes have reported the detection of very-high-energy (VHE) gamma-rays from some gamma-ray bursts (GRBs). One them, GRB 190829A, was triggered by Swift satellite, and about 2 × 104 s after burst onset VHE emission detected H.E.S.S. with ∼5σ significance. This event had unusual features having much smaller isotropic equivalent energy than typical long GRBs achromatic peaks in X-ray optical afterglow at 1.4 103 s. Here, we propose an off-axis jet scenario that explains these observational results. In this model, relativistic beaming effect is responsible for apparently small spectral peak energy. Using a jetted find narrow jet, which has initial Lorentz factor 350 opening half-angle 0.015 rad, viewed can describe observed behaviour afterglow. Another wide, baryon-loaded necessary later-epoch radio emissions. According to our gamma rays may come through synchrotron self-Compton process.