Three-dimensional simulations of long duration gamma-ray burst jets: time scales from variable engines

TL;DR

This study uses 2D and 3D hydrodynamic simulations to explore how unsteady, pulsed jets from gamma-ray burst engines interact with progenitor stars, affecting jet propagation, asymmetry, and observable light curve variability.

Contribution

It provides new insights into how episodic central engines influence jet dynamics and observable properties in long gamma-ray bursts through detailed numerical simulations.

Findings

Unsteady jets are affected by progenitor interaction long after breakout.

Long quiescent times lead to asymmetric pulse and quiescent durations.

Quiescent periods tend to be longer than pulses, explaining observed light curve asymmetries.

Abstract

Gamma-ray burst light curves are characterized by marked variability, each showing unique properties. The origin of such variability, at least for a fraction of long GRBs, may be the result of an unsteady central engine. It is thus important to study the effects that an episodic central engine has on the jet propagation and, eventually, on the prompt emission within the collapsar scenario. Thus, in this study we follow the interaction of pulsed outflows with their progenitor stars with hydrodynamic numerical simulations in both two and three dimensions. We show that the propagation of unsteady jets is affected by the interaction with the progenitor material well after the break-out time, especially for jets with long quiescent times, comparable to or larger than a second. We also show that this interaction can lead to an asymmetric behavior in which pulse durations and quiescent periods are systematically different. After the pulsed jets drill through the progenitor and the interstellar medium, we find that, on average, the quiescent epochs last longer than the pulses (even in simulations with symmetrical active and quiescent engine times). This could explain the asymmetry detected in the light curves of long-quiescent times duration gamma-ray bursts.