The X-ray light curve of Gamma-ray bursts: clues to the central engine

TL;DR

This paper analyzes X-ray light curves of gamma-ray bursts to understand their central engine, comparing different models and identifying features that support a central engine origin, including the magnetar model for certain phases.

Contribution

It provides a detailed analysis of GRB X-ray light curves, comparing flaring and non-flaring cases, and evaluates models like the central engine and magnetar scenarios.

Findings

Steep decay and flares support a central engine origin.

Magnetar model explains shallow decay and plateau luminosity.

Self-similar progenitor structure influences light curve phases.

Abstract

We present the analysis of a large sample of gamma-ray burst (GRB) X-ray light curves in the rest frame to characterise their intrinsic properties in the context of different theoretical scenarios. We determine the morphology, time scales, and energetics of 64 long GRBs observed by \emph{Swift}/XRT \emph{without} flaring activity. We furthermore provide a one-to-one comparison to the properties of GRBs \emph{with} X-ray flares. We find that the steep decay morphology and its connection with X-ray flares favour a scenario in which a central engine origin. We show that this scenario can also account for the shallow decay phase, provided that the GRB progenitor star has a self-similar structure with a constant envelope-to-core mass ratio $\sim 0.02-0.03$. However, difficulties arise for very long duration ($t_p\gtrsim10^4$ s) shallow phases. Alternatively, a spinning-down magnetar whose emitted power refreshes the forward shock can quantitatively account for the shallow decay properties. In particular we demonstrate that this model can account for the plateau luminosity vs. end time anticorrelation.