Gamma-ray bursts spring more surprises
Oct 16, 1998
Two of the most spectacular events in astrophysics - supernovae explosions and gamma-ray bursts - may be related according to three teams of astronomers. The link between certain types of supernovae and gamma-ray bursts has been suggested by the odd behavior of a supernova observed earlier this year. SN1998bw appeared unusually bright at radio wavelengths when it exploded in April. This indicated that the shock wave from the center of the explosion was travelling at relativistic speeds. The astronomers argue that this shock wave was so energetic that it also produced the gamma-ray burst observed on April 25. Indeed, GRB980425 is so different from other gamma-ray bursts that the astronomers say it should have its own classification (Nature 395 663, 670, 672).
There are a number of reasons why GRB980425 is associated with SN1998bw. Both occurred at the same time, at the same location and in the same direction as each other. SN1998bw is also a rare Type Ib/c supernova instead of the more common Type I or Type II explosions. Furthermore, material from the supernova was ejected at significantly higher speeds than standard supernove explosions.
As material from the explosion was ejected, it pushed a shock wave into the local stellar medium. The shocked material then amplified local magnetic fields which, in turn, accelerated the local electrons. This caused the electrons to emit synchrotron radiation. According to the researchers, the first synchrotron radiation produced was in the gamma-ray part of the spectrum, with the radio waves being emitted later as the shock wave slowed down. However, the researchers admit that if the radio emissions are in the form of jets, they may have overestimated the energy of the shock wave, which might cast doubt on the supernova/gamma-ray burst connection.