GRB 031203 afterglow
Gamma-ray bursts were first detected in the late 1960's. These energetic eruptions of gamma radiation initially had no discernable counterpart and it wasn’t until 1997, with the detection of a faint X-ray counterpart of GRB 970228 by the Italian-Dutch satellite BeppoSax, that progress could begin to be made in identifying the origin of these powerful explosions. While a consensus appears to exist to account for the origin of one class of gamma-ray bursts a number of questions remain. The X-ray afterglow of gamma-ray bursts is an important source of information about the radiation processes at play and the environment of the burst. Detecting this afterglow is a great challenge since it fades rapidly.
Just 6 hours after INTEGRAL had alerted the astronomical world to the existence of a new gamma-ray burst, GRB 031203, XMM-Newton turned its instruments towards the region of the explosion. The images obtained by XMM-Newton revealed the first detection of a time-dependent dust-scattered X-ray halo around a gamma-ray burst. Two rings are seen, concentric with the X-ray afterglow, and appearing to expand outwards. In fact, the apparent rate of expansion is a thousand times the speed of light and the two rings are caused by separate dust slabs between the observer and the burst at distances of 880 and 1390 parsecs. The rings appear to expand outwards because light scattered at a larger angle to the line of sight take longer to reach the observer, hence giving the appearance of an expanding circle. This observation provides highly accurate distance determinations to the dust.