GRB 021004 HETE2 Localization
Credit: HETE2 Team; D. Fox (optical transient)

In Real Time

The localization and identification of the mysterious, extraordinarily powerful events known as gamma-ray bursts (GRBs) are some of the primary goals of modern high energy astrophysics. The High Energy Transient Explorer (HETE-2) satellite was built and launched with this goal in mind, and the tenacity of this little observatory has paid off. On October 4 HETE-2 observed a gamma-ray burst with all 3 of its high energy instruments - the FREGATE gamma-ray telescope, the Wide-Field X-ray Monitor (WXM), and the Soft X-ray Camera (SXC). The Fregate telescope provided a detection of the gamma-ray emission but only a coarse localization; the WXM and SXC X-ray cameras provide a measure of the X-ray flux associated with the GRB, and a better position. The image above left shows the "error circles" determined by each instrument- the on-board WXM software provided a fairly good localization from the WXM data, which was refined by scientists on ground. The best localization was provided by the SXC data, which has the smallest "error circle". Using the SXC information observers were able to quickly survey this area with ground based telescopes, and an optical transient was found in the field. The middle image above is an optical picture taken by Derek Fox of Caltech, and comparison of this image with an older image of the same field (shown on the right) clearly shows a bright object (marked by the arrow and "OT" for optical transient) in Fox's picture. Subsequent observations show that this object is associated with a very distant galaxy, which means that the burst must be unbelievably powerful to have been detected at earth.

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Page Author: Dr. Michael F. Corcoran
Last modified October 6, 2002