Evidence for New Relations between Gamma Ray Burst Prompt and X-ray Afterglow Emission from 9 Years of Swift

Abstract

When a massive star explodes as a Gamma Ray Burst information about this explosion is retained in the properties of the prompt and afterglow emission. We report on new relationships between the prompt and X-ray afterglow emission of Swift-detected Gamma Ray Bursts found from BAT and XRT data between 2004 December and 2013 August (754 GRBs). These relations suggest that the prompt and afterglow emission are closely linked. In particular,we find very strong correlations between the BAT 15-150keV $T_{90}$ and the break times before and after the plateau phase in the X-ray 0.3-10keV afterglow light curves. We also find a strong anti-correlation between the photon index of the GRB prompt emission and the X-ray spectral slope of the afterglow. Further, anti-correlations exist between the rest frame peak energy in the prompt emission, E-peak,z, and the X-ray afterglow decay slope during the plateau phase and the break times after the plateau phase. The rest-frame break times before and after the plateau phase are also anti-correlated with the rest-frame 15-150keV luminosity and isotropic energy during the prompt emission. A Principal Component Analysis suggests that GRB properties are primarily driven by the luminosity/energy release in the 15-150 keV band. Luminosity functions derived at various redshifts from logN-logS analysis, indicate that the density of bright bursts is significantly lower in the local Universe compared with the Universeat z$\approx$3, where the density of bright GRBs peaks. Using cluster analysis, we find that the duration of Swift BAT-detected short-duration GRBs is less than 1s. We also present the catalogue of all \swift-onboard detected bursts.

Accepted for publication in the ApJ-Supplement, 66 pages, including 41 figures and 11 tables. We also include the GRB catalog as an ASCII data file named 'grb_catalog_midas.dat' which can be read directly into MIDAS using the format file 'grb_catalog_format.fmt'