Chandra/GRB 991216
Credit: NASA/CXC/Piro et al.

GRB Wrinkles Ironed Out?

Gamma ray bursts (GRBs) are unbelievably power explosions which generate bright flashes of gamma-ray radiation, the most energetic form of electromagnetic radiation. Though a mystery for nearly 30 years, astronomers have made substantial progress in unraveling this mystery by studying the X-ray "afterglows" from GRBs. These X-ray "afterglows" are thought to be produced by the collision of the explosion with the material surrounding the GRB source. Studies of the X-ray afterglows have helped astronomers show that GRBs are occurring in very distant, star forming galaxies far from earth. This allows astronomers to determine how powerful the explosion really is. Previous studies of GRB X-ray afterglows seem to suggest that GRBs are associated with the destruction of extremely massive stars as a violent explosion called a "hypernova". Now the Chandra X-ray observatory has helped confirm this picture by imaging at the highest resolution ever obtained an X-ray afterglow from a burst which occurred on Dec 16, 1999. The Chandra image of GRB 991216 obtained by the ACIS camera by an international team of astronomers led by Luigi Piro has allowed astronomers to study in great detail the energy distribution of the X-ray afterglow, and for the first time has revealed the presence of X-ray emission produced by the element iron. This iron "line emission" (shown as the blue peak in the insert above) allows astronomers to determine the precise location of the afterglow - astronomers calculate that the afterglow is located in a galaxy roughly 8 billion years from earth - so the event that Chandra saw actually occurred 8 billion years prior to Dec 16, 1999! Since the explosion was so distant, it must be extremely powerful to be bright enough to have been seen by Chandra. Astronomers believe the iron rich material seen by Chandra was produced inside an extremely massive star which then died and exploded as a GRB.

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Page Author: Dr. Michael F. Corcoran
Last modified November 6, 2000