Jet precession in gamma-ray bursts: The roles of fallback accretion and disk dynamics

TL;DR

This paper presents a dynamic jet precession model for gamma-ray bursts that accounts for fallback accretion and disk evolution, explaining observed pulse interval variations.

Contribution

It introduces a co-evolution model of fallback accretion and disk dynamics affecting jet precession, advancing understanding of GRB temporal profiles.

Findings

Precession period decreases then increases during fallback.

Higher viscosity and slower spin extend precession periods.

Model fits explain increasing pulse intervals in GRB light curves.

Abstract

The precession phenomenon of the jet in a gamma-ray burst (GRB) is a key probe of the physics of the central engine. Previous studies generally assumed a fixed precession period when analysing the temporal profiles in GRBs; however, the dynamic evolution of the fallback process and accretion disk can significantly affect the precession behaviour. In this work we present a jet precession model that incorporates the co-evolution of fallback accretion and the central black hole (BH). Our model demonstrates that the jet precession period initially decreases rapidly during the early fallback phase and subsequently increases nearly linearly as the disk evolves. We find that a higher accretion disk viscosity and a slower BH spin lead to longer precession periods and faster precession period growth rates, and that the geometric structure of the precession system modulates the pulse amplitude of the light curve. By fitting the model to observational data of GRBs with multi-pulse structures, we show that jet precession can naturally explain the increasing pulse intervals and broadened pulse widths observed in both long and short GRBs.