Imagine the Universe!

Look, There in the Sky! It's a Gamma-Ray Burster?

27 March 1997

Look, There in the Sky! It's a Gamma-Ray Burster?

What exactly is the source of a gamma-ray burst? Since their discovery in the early 1970s, nobody has been able to explain the cause of the mysterious flash of gamma-rays called a gamma-ray burst that seems to come from a random direction on the sky. Worse yet, it is even unclear whether these high-energy explosions originate in our own Galaxy or in distant galaxies across the Universe. Now, all of that may have changed!

BeppoSAX Image of GRB Source
Credit: BeppoSAX/ISA/ESA

On February 28, the Italian/Dutch satellite known as BeppoSAX detected what may well be X-rays from a burst source, eight hours after the gamma-ray flash. The discovery image from BeppoSAX, ISA, and ESA is shown above. Even later, using the position provided by this X-ray image, ground-based telescopes discovered a variable optical source which also seems to be related to the burster. Dramatically, this optical transient has now faded. In its place lies a steady source which appears to be a dim, distant galaxy.

Did the gamma-ray burst originate in the distant galaxy? If so, it answers one facet of one of modern astronomy's greatest controversies. If not, this would not be the first fortuitous coincidence to mislead astronomers. Only repeated observations of events such as those seen by BeppoSAX and ground-based observatories will be able to determine if this is a major breakthrough for high-energy astronomy or just frustratingly bad luck.

For more information, see the press release from the Italian Space Agency (

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Acting Project Leader: Dr. Barbara Mattson
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