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Homing In on the Elusive Source of Gamma-Ray Bursts

Dutch and Italian astronomers are closing the net on the culprits behind one of astronomy's greatest mysteries: gamma-ray bursts.

Since their discovery almost 30 years ago, over 1000 of these bursts have been observed at random positions in the sky. But astronomers don't have the faintest idea whether they originate near our Milky Way galaxy or in the far reaches of the universe. Because most gamma detectors have a very low positional accuracy, it has never been possible to identify a burst with a known astronomical object like a galaxy or a star.

But hunters of these strange beasts drew a sharper bead on a recent one. In the early morning of Friday, 28 February, a burst of gamma rays erupted in the constellation Orion, lighting up a detector aboard the Italian-Dutch satellite Beppo-SAX. At the same time, one of the satellite's two Dutch wide-field x-ray cameras, which have a much sharper resolution than the gamma detector, caught the burst, enabling scientists to narrow the search. Eight hours later, controllers pointed the satellite's sensitive narrow-field x-ray cameras at the suspect position, revealing a rapidly dimming x-ray source that hadn't been there before.

Beppo-SAX had apparently caught the first glimpse ever of the object responsible for the original blast as it cooled off, detecting it just before it vanished. "Had the burst occurred over the weekend, we wouldn't have been able to respond so quickly," says John Heise of the Utrecht laboratory of SRON (Space Research Organization Netherlands), the project scientist for the wide-field x-ray cameras.

The detection has sparked a flurry of activity at observatories worldwide to try to nail down what kind of object may have produced the burst. Dale Frail of the National Radio Astronomy Observatory, for example, observed the burst region with the Very Large Array radio telescope near Socorro, New Mexico. Frail reports that measurements on 1 and 4 March reveal a suspect radio source. But according to Heise, it's too early to say for sure whether this source is related to the gamma-ray burst.