Modeling Gamma-ray burst Afterglow observations with an Off-axis Jet emission

TL;DR

This paper develops an analytical and numerical model for off-axis gamma-ray burst afterglows, successfully explaining delayed emissions and providing constraints on future observations, including gravitational-wave events.

Contribution

It introduces a combined analytical and hydrodynamical approach to model off-axis GRB afterglows, improving understanding of their long-lasting emissions.

Findings

Numerical simulations agree with analytical models.

The model explains delayed non-thermal emissions in GRBs.

Constraints on afterglow emissions from multi-wavelength upper limits.

Abstract

Gamma-ray bursts (GRBs) are fascinating extragalactic objects. They represent a fantastic opportunity to investigate unique properties not exhibited in other sources. Multi-wavelength afterglow observations from some short- and long-duration GRBs reveal an atypical long-lasting emission that evolves differently from the canonical afterglow light curves favoring the off-axis emission. We present an analytical synchrotron afterglow scenario, and the hydrodynamical evolution of an off-axis top-hat jet decelerated in a stratified surrounding environment. The analytical synchrotron afterglow model is shown during the coasting, deceleration (off- and on-axis emission), and the post-jet-break decay phases, and the hydrodynamical evolution is computed by numerical simulations showing the time evolution of the Doppler factor, the half-opening angle, the bulk Lorentz factor, and the deceleration radius. We show that numerical simulations are in good agreement with those derived with our analytical approach. We apply the current synchrotron model and describe successfully the delayed non-thermal emission observed in a sample of long and short GRBs with evidence of off-axis emission. Furthermore, we provide constraints on the possible afterglow emission by requiring the multi-wavelength upper limits derived for the closest Swift-detected GRBs and promising gravitational-wave events.