Temporal variability of GRB early X-ray afterglows and GRB080319B prompt emission

TL;DR

This study systematically analyzes the early X-ray afterglows of GRBs and the prompt emission of GRB080319B, revealing variability on sub-second scales and evolution of variability during prompt emission.

Contribution

First systematic search for minimum variability timescales in early X-ray afterglows using power spectrum analysis, revealing rapid variability down to about 1 second.

Findings

Early XRT afterglows exhibit variability on ~1 second timescales.

The shortest variability timescale correlates with higher energy bands.

GRB080319B's prompt emission shows a characteristic variability timescale of about 1 second, evolving during the burst.

Abstract

We performed the first systematic search for the minimum variability time scale between 0.3 and 10 keV studying the 28 brightest early (<3000 s) afterglows detected by Swift-XRT up to March 2008. We adopt the power spectrum analysis in the time domain: unlike the Fourier spectrum, this is suitable to study the rms variations at different time-scales. We find that early XRT afterglows show variability in excess of the Poissonian noise level on time-scales as short as about 1 s (rest frame value), with the shortest t_{min} associated with the highest energy band. The gamma-ray prompt emission of GRB080319B shows a characteristic average variability time-scale t_{var} of about 1s; this parameter undergoes a remarkable evolution during the prompt emission (BAT observation).