Internal Energy Dissipation of Gamma-Ray Bursts Observed with Swift: Precursors, Prompt Gamma-rays, Extended emission and Late X-ray Flares

TL;DR

This study analyzes Swift GRB data to explore internal energy dissipation processes, revealing that various emission episodes likely originate from repeated central engine activation, with implications for understanding GRB progenitors and jet mechanisms.

Contribution

It provides a comprehensive joint analysis of gamma-ray and X-ray data, linking different emission components to a common physical origin and highlighting the importance of early X-ray detection.

Findings

Precursor emission detected in ~10% of GRBs, associated with massive star core-collapse.

Extended emission is linked to compact star merger origins.

X-ray emission observed before gamma-ray peaks, indicating early engine activity.

Abstract

We jointly analyze the gamma-ray burst (GRB) data observed with BAT and XRT on board the Swift mission to present a global view on the internal energy dissipation processes in GRBs, including precursors, prompt gamma-ray emission, extended soft gamma-ray emission, and late X-ray flares. The Bayesian block method is utilized to analyze the BAT lightcurves to identify various emission episodes. Our results suggest that these emission components likely share a same physical origin, which is repeated activation of the GRB central engine. What we observe in the gamma-ray band may be the tip-of-iceberg of more extended underlying activities. The precursor emission, which is detected in about 10% of {\em Swift} GRBs, is preferably detected in those GRBs that have a massive star core-collapse origin. The soft extended emission (EE) tail, on the other hand, is preferably detected in those GRBs that have a compact star merger origin. Bright X-ray emission is detected during the BAT quiescent phases prior to subsequent gamma-ray peaks, implying that X-ray emission may be detectable prior the BAT trigger time. Future GRB alert instruments with soft X-ray capability would be essential to reveal the early stage of GRB central engine activities, sheding light into jet composition and jet launching mechanism in GRBs.