Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs

TL;DR

This paper provides a comprehensive homogeneous X-ray analysis of 318 GRBs observed by Swift-XRT, introducing new methods and tools for data processing, and discusses the implications of the results for GRB emission models.

Contribution

It presents a large, uniform dataset of GRB X-ray observations along with novel analysis methods and web tools for broader community use.

Findings

Evidence for a common underlying behavior in GRB light curves

Range of light curve morphologies explained by external forward shock models

Energy injection may need to continue for days to weeks in GRB afterglows

Abstract

We present a homogeneous X-ray analysis of all 318 Gamma Ray Bursts detected by the X-ray Telescope on the Swift satellite up to 2008 July 23; this represents the largest sample of X-ray GRB data published to date. In Sections 2--3 we detail the methods which the Swift-XRT team has developed to produce the enhanced positions, light curves, hardness ratios and spectra presented in this paper. Software using these methods continues to create such products for all new GRBs observed by the Swift-XRT. We also detail web-based tools allowing users to create these products for any object observed by the XRT, not just GRBs. In Sections 4--6 we present the results of our analysis of GRBs, including probability distribution functions of the temporal and spectral properties of the sample. We demonstrate evidence for a consistent underlying behaviour which can produce a range of light curve morphologies, and attempt to interpret this behaviour in the framework of external forward shock emission. We find several difficulties, in particular that reconciliation of our data with the forward shock model requires energy injection to continue for days to weeks.