Simultaneous prompt optical and gamma-ray emission: GRB 090727

The standard theoretical model of Gamma‐Ray Bursts (GRBs) predicts that high energy gamma‐ray emission is produced by internal shocks and that afterglow emission at longer wavelengths is produced later by external shocks, i.e., prompt emission and afterglow are coming from different regions. This is usually the case in typical light curves (LCs), where gamma‐ray/hard X‐ray data evolve differently with time than soft X‐ray and optical data. But there are cases like GRB 090727 which show that X‐ray/optical emission could be produced simultaneously with gamma‐ray emission. Some of these GRBs show very similar properties in LCs, for instance peaks occurring at the same time in optical, X‐ray and gamma‐ray regime. This favours the idea that we could be dealing with radiation at very different frequencies all coming from single emission region. We focus our attention on GRB 090727 which shows what looks like correlated optical, X‐ray and gamma‐ray emission, but we also discuss similar GRBs and possible scenarios and implications for the standard model.