Reverse Shock Emission from Misaligned Structured Jets in Gamma-Ray Bursts

TL;DR

This paper explores how reverse shock emissions influence off-axis gamma-ray burst afterglows, revealing their potential to produce distinctive light curve features like double peaks, depending on jet structure and viewing angle.

Contribution

It introduces a comprehensive model for reverse shock emission in various jet structures and applies it to GW170817, highlighting its significance in early afterglow observations.

Findings

Reverse shock can significantly affect early afterglow brightness.

Light curves may show double peaks or single peaks with prominent features.

Jet structure and viewing angle critically influence observed light curves.

Abstract

The afterglow of gamma-ray bursts (GRBs) has been extensively discussed in the context of shocks generated during an interaction of relativistic outflows with their ambient medium. This process leads to the formation of both a forward and a reverse shock. While the emission from the forward shock, observed off-axis, has been well-studied as a potential electromagnetic counterpart to a gravitational wave-detected merger, the contribution of the reverse shock is commonly overlooked. In this paper, we investigate the contribution of the reverse shock to the GRB afterglows observed off-axis. In our analysis, we consider jets with different angular profiles, including two-component jets, power-law structured jets, Gaussian jets and 'mixed jets' featuring a Poynting-flux-dominated core surrounded by a baryonic wing. We apply our model to GRB 170817A/GW170817 and employ the Markov Chain Monte Carlo (MCMC) method to obtain model parameters. Our findings suggest that the reverse shock emission can significantly contribute to the early afterglow. In addition, our calculations indicate that the light curves observable in future off-axis GRBs may exhibit either double peaks or a single peak with a prominent feature, depending on the jet structure, viewing angle and micro-physics shock parameters.