A comprehensive statistical analysis of Swift X-ray light-curves: the prompt-afterglow connection in Gamma-Ray Bursts

TL;DR

This study analyzes over 650 Swift X-ray light-curves of Gamma-Ray Bursts to explore the connection between prompt emission and afterglow, revealing differences between short and long GRBs and identifying a universal scaling relation across GRB types.

Contribution

It provides the first comprehensive statistical analysis of Swift X-ray light-curves, uncovering relations linking prompt and afterglow properties and highlighting differences between short and long GRBs.

Findings

Short GRBs decay faster and are less luminous than long GRBs.

A universal 3-parameter scaling relation exists across GRB types.

Short GRBs are outliers in most prompt-afterglow relations.

Abstract

We present a comprehensive statistical analysis of Swift X-ray light-curves of Gamma-Ray Bursts (GRBs), with more than 650 GRBs. Two questions drive this effort: (1) Does the X-ray emission retain any kind of memory of the prompt phase? (2) Where is the dividing line between long and short GRBs? We show that short GRBs decay faster, are less luminous and less energetic than long GRBs, but are interestingly characterized by very similar intrinsic absorption. Our analysis reveal the existence of a number of relations that link the X-ray to prompt parameters in long GRBs; short GRBs are outliers of the majority of these 2-parameter relations. Here we concentrate on a 3-parameter (E_pk-Egamma,iso-E_X,iso) scaling that is shared by the GRB class as a whole (short GRBs, long GRBs and X-ray Flashes -XRFs): interpreted in terms of emission efficiency, this scaling may imply that GRBs with high $E_{\rm{pk}}$ are more efficient during their prompt emission.