Time delays between Fermi LAT and GBM light curves of GRBs

Understand

Most Gamma-Ray Bursts (GRBs) detected by the Fermi Gamma-ray Space Telescope exhibit a delay of up to about 10 seconds between the trigger time of the hard X-ray signal as measured by the Fermi GBM and the onset of the MeV-GeV counterpart detected by the LAT.

• This delay may hint at important physics, whether it is due to the intrinsic variability of the inner engine or it is related to quantum dispersion effects in the velocity of light propagation from the sources to the observer.
• It is critical to have a proper assessment of how these time delays affect the overall properties of the light curves.
• We cross-correlated the 5 brightest GRBs of the 1st Fermi LAT Catalog by means of the continuous correlation function (CCF) and of the Discrete Correlation Function (DCF).