Jul 5 – 10, 2021
Europe/Rome timezone

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

Jul 6, 2021, 9:10 AM
Talk in the parallel session Unusual and New Types of Gamma-ray Bursts Unusual and New Types of Gamma-Ray Bursts


Yuri Sato (Aoyama Gakuin University)


Recently, ground-based Imaging Atmospheric Cherenkov Telescopes, such as MAGIC and H.E.S.S., have reported the detection of very-high-energy (VHE) gamma-rays from three gamma-ray bursts (GRB 180720B, 190114C, 190829A). One of them, GRB 190829A, was triggered by the Swift satellite, and about 20000 s after the burst onset the VHE gamma-ray emission was detected by H.E.S.S. with ~ 5 sigma significance. This event had more unusual features than the other VHE gamma-ray events. First, it had much smaller isotropic equivalent gamma-ray energy than typical long gamma-ray bursts and is classified as low luminosity GRB. Second, early X-ray and optical afterglow emission showed a rising part and simultaneously peaked at about 1400 s. We propose an off-axis jet scenario that explains these observational results. In this model, the relativistic beaming effect is responsible for the apparently small isotropic gamma-ray energy and spectral peak energy. Using a jetted afterglow model, we find that the narrow jet, which has the initial Lorentz factor of 350 and the initial jet opening half-angle of 0.015 rad, viewed off-axis can describe the observed achromatic behavior in the X-ray and optical afterglow. Another wide, baryon-loaded jet is necessary for the later-epoch X-ray and radio emissions. Also, we suggest that some of low luminosity GRBs could be explained by off-axis jet scenario.

Primary author

Yuri Sato (Aoyama Gakuin University)


Kaori Obayashi (Aoyama Gakuin University) Ryo Yamazaki (Department of Physical Sciences, Aoyama Gakuin University) Kohta Murase (Pennsylvania State University) Yutaka Ohira (Tokyo University)

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