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

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 ∼1 s (rest frame value), with the shortest t_min associated with the highest energy band. The γ—ray prompt emission of GRB 080319B shows a characteristic average variability time-scale <t_var>∼1 s; this parameter undergoes a remarkable evolution during the prompt emission (BAT observation). [ABSTRACT FROM AUTHOR]