From the earliest pulses to the latest flares in long GRBs

TL;DR

This paper investigates the origins of gamma-ray pulses and X-ray flares in long GRBs, showing that both are consistent with internal shocks, and challenges the need for a long-lasting central engine.

Contribution

It demonstrates that X-ray flares can be produced by internal shocks, reducing the necessity of a long-lasting central engine in GRB models.

Findings

Prompt gamma-ray pulse duration is constant over time.

X-ray flare properties are consistent with internal shock origin.

No correlation between pulse duration and occurrence time supports internal origin.

Abstract

The prompt emission of Gamma Ray Bursts extends from the early pulses observed in gamma-rays (>15 keV) to very late flares of X-ray photons (0.3-10 keV). The duration of prompt gamma-ray pulses is rather constant while the width of X-ray flares correlates with their peak time suggesting a possible different origin. However, pulses and flares have similar spectral properties. Considering internal and external shock scenarios, we derive how the energy and duration of pulses scale with their time of occurrence and we compare with observations. The absence of an observed correlation between prompt emission pulse duration and its time of occurrence favours an "internal" origin and confirms the earlier results of Ramirez-Ruiz & Fenimore. We show that also the energetic and temporal properties of X-ray flares are consistent with being produced by internal shocks between slow fireballs with a small contrast between their bulk Lorentz factors. These results relax the requirement of a long lasting central engine to explain the latest X-ray flares.