Whereas standard science analyses with the Fermi Large Area Telescope (LAT) are restricted to well-reconstructed events, the LLE (LAT Low Energy) event selection is based on relaxed criteria which offer a much higher effective area below 100 MeV. As this new event selection also increases the background levels, it can be used in case of impulsive celestial sources such as the prompt emission of Gamma-Ray Bursts (GRBs) which provide high signal-to-noise ratios.

The LLE data have been publicly released for 23 GRBs (and 5 solar flares) so far. They will allow any scientist interested in the LAT observations of GRBs to better study their temporal and spectral properties, especially for GRBs with faint emission above 100 MeV and/or observed at inclinations larger than 65 deg in the LAT field of view. We will present a validation study of the Monte-Carlo simulations which are used to derive the LLE Instrument Response Functions (effective area, energy resolution and Point Spread Function), with particular emphasis on the estimation of the associated systematic uncertainties which are relevant for GRB spectral reconstruction based on LLE data.