Energy injection driven by precessing jets in gamma-ray burst afterglows

TL;DR

This paper investigates how precessing jets in gamma-ray bursts can periodically inject energy into afterglows, affecting their light curves and potentially explaining observed features like plateaus and bumps.

Contribution

It introduces jet precession as a new energy injection mechanism in GRB afterglows and explores its effects through modeling with various parameters.

Findings

Precessing jets can cause shallow decay or plateau segments in afterglow light curves.

Giant bumps in light curves can result from jets sweeping across the line of sight.

Precessing jets may explain X-ray transients without associated GRBs.

Abstract

Jet precession is considered to universally exist in different-scale astronomical phenomena, including gamma-ray bursts (GRBs). For the long-lived GRB central engine, the relativistical precessing jets will periodically inject kinetic energy into the external shocks, then significantly modulate the shapes of the light curves (LCs) in GRB afterglows. In this paper, we adopt the standard external shock model to investigate the effects of jet precession on GRB X-ray afterglows in cases with different parameters, i.e., the steady or time-dependent jet powers, precession periods, precession angles, and viewing angles. In the case where the jet powers are in steady or slow decay and the jet can sweep across the line of sight, shallow decay (or plateau) segments should appear; otherwise, a giant bump will emerge in the GRB afterglow LCs. We show that jet precession is a new plausible mechanism of the energy injection in GRBs. Moreover, some observed X-ray transients without GRB associations might be powered by the precessing jets.