The source of Gamma Ray bursts is currently unknown.  They are a surprising phenomenon because gamma rays are so powerful that very few events could cause them.  They have also only been recently discovered by projects like the Compton Gamma Ray Observatory, and appear to be coming from all directions, not just in the galactic plane.\nThis would indicate a phenomenon that has extra-galactic origins... for example, activity inside of an active galactic nuclei, or quasars.\nBecause they happen at random intervals, abd are ephemeral (often just a few seconds), and the "scopes" used to capture them are not tightly directional, we don't have any instruments currently that can figure out exactly what they are.  For now that means, the best we can do is hypothesize based on what cosmic events we believe are of the appropriate magnitude to tigger gamma rays.
what are gamma ray bursts?