Gamma Ray Bursts and Super-novas

Although the issue of whether some or most gamma-ray-burst (GRB) objects lie at extragalactic distances has been settled (they do), the question of what they are is still a mystery. Two new results reported in the 3 November issue of Science support the idea that supernovas are responsible in some way. X-ray spectra from one GRB recorded by the BeppoSAX satellite (Amati et al.) and from another GRB as recorded by the Chandra satellite (Piro et al.) detect the presence of iron, which is made in supernovas. The trouble is that there seems to be a delay (of some years) between the time of the GRB and the time of the supernova. A new hypothesis to account for the delay is offered by Mario Vietri of the Third University of Rome and Luigi Stella of the Astronomical Observatory of Rome. They believe the star in question has collapsed twice. In their "supranova" model a rapidly rotating supermassive star collapses first to a neutron star, scattering a debris cloud as it does so. Later the neutron star collapses into a black hole, unleashing a gamma burst which illuminates the debris shell left from the first collapse.