Can Internal Shocks Produce the Variability in Gamma-Ray Bursts?

We discuss the possibility that gamma-ray bursts result from internal shocks in ultrarelativistic matter. Using a simple model, we calculate the temporal structure and estimate the efficiency of this process. In this model the flow of ultrarelativistic matter is represented by a succession of shells with random values of the Lorentz factor. We calculate the shocks that take place between those shells, and we estimate the resulting emission. Internal shocks can produce the highly variable temporal structure observed in most of the bursts, provided that the source emitting the relativistic flow is highly variable. The observed peaks are in almost one-to-one correlation with the activity of the emitting source. A large fraction of the kinetic energy is converted to radiation. The most efficient case is when an inner engine produces shells with comparable energy but very different Lorentz factors. It also gives the most desirable temporal structure.