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

Much of the progress in understanding gamma-ray bursts (GRBs) has come from studies of distant events (redshift z approximate to 1). In the brightest GRBs, the gamma-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 gamma-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 gamma-ray energy of less than or equal to 10(50) 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 relation(3,4) and luminosity/spectral-lag relations(5,6) that describe the majority of GRBs. Radio calorimetry shows that both of these events are under-energetic explosions(7). We conclude that there does indeed exist a large population of under-energetic events.