  In this paper we numerically examine the connection of the Gallavotti-Cohen
fluctuation formula and the functional form of the corresponding probability
density function in the field driven Lorentz gas thermostated by the Gaussian
isokinetic thermostat. We analyze the moments of the entropy production rate
fluctuations and show that all the central moments of the averaged fluctuations
exhibit power law dependence on the length of the averaging time interval,
indicating that this density deviates from a Gaussian. Furthermore the obtained
exponents are found to obey a special pairing rule showing that the
corresponding probability density function can not be scaled in the averaging
time interval.
