  We apply Fourier analysis to 214 light curves of long gamma-ray bursts and
study the statistical properties of their power density spectra (PDSs). The
averaged PDS is found to follow a power law of index -5/3 over almost 2 decades
of frequency with a break at about 2 Hz. Individual PDSs are exponentially
distributed around the power law. It provides evidence that the diversity of
the bursts is due to random realizations of the same process which is
self-similar over the full range of time-scales. The -5/3 slope of the average
spectrum may indicate that gamma-ray bursts are related to a phenomenon well
studied in hydrodynamics - fully developed turbulence.
