WFC Science highlights - Gamma-ray burst 980425

Due to an unfavorable star tracker configuration, GRB 980425 could not be localized with WFC to better than an 8' radius error box. The follow up observations with the narrow field instruments on BeppoSAX revealed two weak X-ray sources inside this error box.

To the surprise of many, Galama (University of Amsterdam) discovered a supernova explosion (SN1998bw) coincident with one of the two NFI sources and coincident in time with GRB to within a few days. The explosion occurred inside a relatively nearby galaxy (z=0.0085) which is in strong contrast to 5 other GRBs whose distance could be determined and which have a distance z>0.835. This implies a total gamma-ray energy output of only 1048 ergs, again in strong contrast to the cosmological bursts with outputs of up to 1054 ergs. This points to a different physical mechanism at work, as well as a diversity in GRBs.

The various error boxes of GRB 980425 overlayed on a DSS image. The large circle is the WFC error box. Courtesy Titus Galama (UvA).

Jean in 't Zand, SRON, March 12, 1999