Evidence of Exponential Decay Emission in the Swift Gamma-ray Bursts

TL;DR

This study analyzes Swift GRB data, confirming an exponential decay component in the steep emission phase that connects prompt and afterglow emissions, offering insights into the decay mechanisms.

Contribution

It introduces a novel method of extrapolating XRT data into BAT energy range and confirms the exponential decay component in GRB emission profiles.

Findings

Exponential decay component connects BAT prompt and XRT steep decay.

Some GRBs' steep decay fits a power-law with exponential decay.

Discussion of decay component within internal and external shock models.

Abstract

We present a systematic study of the steep decay emission from gamma-ray bursts (GRBs) observed by the Swift X-Ray Telescope (XRT). In contrast to the analysis described in recent literature, we produce composite Burst Alert Telescope (BAT) and XRT light curves by extrapolating the XRT data (2-10 keV) into the BAT energy range (15-25 keV) rather than extrapolating the BAT data into the XRT energy band (0.3-10 keV). Based on the fits to the composite light curves, we have confirmed the existence of an exponential decay component which smoothly connects the BAT prompt data to the XRT steep decay for several GRBs. We also find that the XRT steep decay for some of the bursts can be well fit by a combination of a power-law with an exponential decay model. We discuss this exponential component within the frame work of both the internal and the external shock model.