Lightcurves of cosmological gamma-ray bursts

It is shown that in a typical fireball of cosmological GRB a neutron compon ent is initially present and has the energy of the order of the proton-elec tron component. Free neutrons change essentially the dynamics of a relativi stic shock formed by the ejected material in the surrounding medium. The ne utron flow may decouple from the proton one or may not. Also, neutrons may decay before the shock of proton origin decelerates significantly or after that. According to these possibilities there are four types of bursts posse ssing lightcurves with different global appearance. We point out a number o f lightcurve features expected to be correlated. For example, the height, d elay time and duration of the secondary pulse are related to each other. We show that two-peaked lightcurves may be as common as single-peaked ones.