Beaming in Gamma-Ray Bursts: Evidence for a Standard Energy Reservoir

TLDR

The study compiles all GRB afterglows with known distances and determines their jet opening angles from broadband light‑curve breaks. Using a conical jet model, the authors correct for geometry and show that the true gamma‑ray energy release clusters around 5 × 10^50 ergs. They conclude that GRB engines release energies similar to supernovae, that the wide fluence and luminosity spread is mainly due to varying opening angles, and that only a small fraction are observable, implying a true GRB rate hundreds of times higher than observed.

Abstract

We present a comprehensive sample of all gamma-ray burst (GRB) afterglows with known distances, and we derive their conical opening angles based on observed broadband breaks in their light curves. Within the framework of this conical jet model, we correct for the geometry and we find that the gamma-ray energy release is narrowly clustered around 5 × 1050 ergs. We draw three conclusions. First, the central engines of GRBs release energies that are comparable to ordinary supernovae. Second, the broad distribution in fluence and luminosity for GRBs is largely the result of a wide variation of opening angles. Third, only a small fraction of GRBs are visible to a given observer, and the true GRB rate is several hundred times larger than the observed rate.