Determining the viewing angle from TeV light curve of GRB 221009A

TL;DR

This paper analyzes the TeV light curve of GRB 221009A to determine its viewing angle, using models with and without high-latitude radiation, revealing a near on-axis viewing configuration.

Contribution

It introduces two models to estimate the GRB's viewing angle from TeV light curves, considering high-latitude radiation effects.

Findings

Viewing angles are approximately 9.4e-4 and 5.9e-3 radians.

The estimated angles suggest an on-axis observation.

Models fit the observed jet break in the light curve.

Abstract

Gamma-ray bursts (GRBs) are among the most powerful explosive events in the universe. LHAASO recently observed the most luminous one: GRB 221009A, and unveiled its TeV light curve. The light curve exhibits a distinct jet break at around 670 seconds, enabling the derivation of the viewing angle based on the smoothness of the jet break. We constructed two models with or without considering the high-latitude radiation, where the viewing angle was treated as a free parameter, to fit the TeV light curve. We obtained the viewing angles being 9.4 $\times 10^{-4}$ radians and 5.9 $\times 10^{-3}$ radians, respectively. These values closely resemble an on-axis scenario, given the opening angle is 1.4 $\times 10^{-2}$ radians.