The sub-energetic gamma-ray burst GRB 031203 as a cosmic analogue to the nearby GRB 980425

Abstract

Over the six years since the discovery(1) of the gamma-ray burst GRB 980425, which was associated(2) with the nearby ( distance similar to40 Mpc) supernova 1998bw, astronomers have debated fiercely the nature of this event. Relative to bursts located at cosmological distance ( redshift z approximate to 1), GRB 980425 was under-luminous in gamma-rays by three orders of magnitude. Radio calorimetry(3,4) showed that the explosion was sub-energetic by a factor of 10. Here we report observations of the radio and X-ray afterglow of the recent GRB 031203 ( refs 5 - 7), which has a redshift of z = 0.105. We demonstrate that it too is sub-energetic which, when taken together with the low gamma-ray luminosity(7), suggests that GRB 031203 is the first cosmic analogue to GRB 980425. We find no evidence that this event was a highly collimated explosion viewed off-axis. Like GRB 980425, GRB 031203 appears to be an intrinsically sub-energetic gamma-ray burst. Such sub-energetic events have faint afterglows. We expect intensive follow-up of faint bursts with smooth gamma-ray light curves(8,9) ( common to both GRB 031203 and 980425) to reveal a large population of such events.