where are the gamma rays?
Long-duration gamma-ray bursts are associated with peculiar supernova explosions and a long-lived radio afterglow emission has been detected for some of them. So the discovery of relativistic radio ejecta from two supernovae not associated with detected gamma-ray bursts is a surprise. Did the gamma rays point away from Earth or were they trapped inside the star? Gamma-ray bursts lasting more than several seconds are associated with peculiar supernova explosions of massive stars. They are thought to be generated by a central engine that is likely to be a newborn black hole at the heart of the dying star (CERN Courier September 2003 p15). These supernovae are all of spectral type Ibc (i.e. either Ib or Ic), which means that they are core-collapse supernovae with no evidence of hydrogen lines in the spectrum, suggesting that the massive star has previously blown away its outer envelope of hydrogen. Only about 1% of type Ibc supernovae display gamma-ray bursts and evidence for relativistic
