  We search for possible time lags caused by quantum gravitational (QG) effects
using gamma-ray bursts (GRBs) detected by INTEGRAL. The advantage of this
satellite is that we have at our disposal the energy and arrival time of every
detected single photon, which enhances the precision of the time resolution. We
present a new method for seeking time lags in unbinned data using a maximum
likelihood method and support our conclusions with Monte Carlo simulations. The
analysis of the data yields a mass scale well below the Planck mass whose value
may however increase if better statistics of GRBs were available. Furthermore,
we disagree with previous studies in which a non-monotonic function of the
redshift was used to perform a linear fit.
