An apparently normal γ-ray burst with an unusually low luminosity

Much of the progress in understanding γ-ray bursts (GRBs) has come from studies of distant events (redshift z ≈ 1). In the brightest GRBs, the γ-rays are so highly collimated that the events can be seen across the Universe. It has long been suspected that the nearest and most common events have been missed because they are not as collimated or they are under-energetic (or both)1. Here we report soft γ-ray observations of GRB 031203, the nearest event to date (z = 0.106; ref. 2). It had a duration of 40 s and peak energy of >190 keV, and therefore appears to be a typical long-duration GRB. The isotropic γ-ray energy of ≤1050 erg, however, is about three orders of magnitude smaller than that of the cosmological population. This event—as well as the other nearby but somewhat controversial GRB 980425—is a clear outlier from the isotropic-energy/peak-energy relation3,4 and luminosity/spectral-lag relations5,6 that describe the majority of GRBs. Radio calorimetry shows that both of these events are under-energetic explosions7. We conclude that there does indeed exist a large population of under-energetic events.