Prior Emission Model for X-ray Plateau Phase of Gamma-Ray Burst Afterglows

TL;DR

This paper proposes a two-component emission model for gamma-ray burst afterglows, attributing the plateau phase to prior emission from the central engine, and suggests observational tests for this hypothesis.

Contribution

It introduces a novel two-component model explaining the plateau phase as prior emission, linking it to central engine activity before the main burst.

Findings

The plateau phase is caused by prior emission from the central engine.

Transition from plateau to normal decay is due to zero-time choice.

Prior emission may be observable 10^3-10^4 seconds before the main burst.

Abstract

The two-component emission model to explain the plateau phase of the X-ray afterglows of gamma-ray bursts (GRBs) is proposed. One component, which is responsible for the plateau and subsequent normal decay phase of the X-ray afterglow, is the prior emission via outflow ejected from the central engine before the main burst. The other is the main outflow, which causes the prompt GRB emission and the initial steep decay phase of the X-ray afterglow. In this model, the transition from the plateau to the subsequent normal decay phase is an artifact of the choice of the zero of time. For events with distinct plateau phase, the central engine is active 10^3-10^4 sec before the launch of the main outflow. According to this model, a prior emission in the X-ray and/or optical bands 10^3-10^4 sec before the prompt GRB emission is possibly seen, which will be tested by near-future instruments such as Monitor of All-sky X-ray Image (MAXI), WIDe-field telescope for GRB Early Timing (WIDGET), and so on.