Gamma-ray bursts (GRBs) are the most powerful outbursts of electromagnetic radiation in our Universe. A subset of GRBs are accompanied by precursors, dim gamma-ray flashes that precede the main outburst by tens to hundreds of seconds. We present an analysis of 11 years of Fermi-GBM data to identify these precursor flashes. For each of the 2364 analyzed GRBs, a time window of 2000 s centered on the GRB trigger was examined using a Bayesian block method. 217 GRBs (9%) with precursor emission were identified. Our results indicate that long bursts (T90$>2$ s) are $\sim$10 times more likely to be preceded by a precursor than short bursts. In addition, we show that the distribution of the quiescent time, separating the precursor and the prompt (main emission) phase, is well modeled by a double Gaussian function. This suggests that at least two physical mechanisms contribute to the observed precursor flashes. One noteworthy GRB with precursor emission in our sample is the ultra-bright GRB 190114C, for which TeV gamma rays were observed by the MAGIC telescope. Our results, including the emission times and light curves of the identified precursors, have been made available via the GRBweb online tool (https://icecube.wisc.edu/~grbweb_public/Precursors.html).
GRB; precursor; Fermi; GBM