Scientists from around the world have taken advantage of NASA teamwork to quickly locate and observe a gamma ray burst -- one of the most violent events in the universe.
Astronomers pinpointed the precise location of the blast on Dec. 16, 1999, by using coordinated observations from the Burst and Transient Source Experiment (BATSE) managed by NASA's Marshall Space Flight Center in Huntsville, Ala., and the Rossi X-ray Timing Explorer operated by NASA's Goddard Space Flight Center in Greenbelt, Md.
"This is the first major success in using instruments on two NASA satellites to locate a burst quickly," said Dr. Marc Kippen, a University of Alabama in Huntsville astrophysicist working on the BATSE team at the Marshall Center.
It can take several hours to reprogram a spacecraft to point to a source. By then the afterglow left by the burst explosion is usually too faint to be detected. That is why Marshall's Burst Experiment, designed specifically to detect elusive gamma ray bursts, is usually the first -- and sometimes only -- instrument to detect these mysterious explosions.
The Burst Experiment apparatus includes eight detector modules mounted on the corners of NASA's Compton Gamma Ray Observatory orbiting Earth. BATSE's ability to see gamma ray bursts across most of the universe has given scientists the most information ever obtained on bursts. But the detectors' ability to see gamma ray bursts across most of the universe reduces their precision in determining burst locations.
To locate bursts more accurately, Marshall's BATSE team worked with the Rossi Explorer team to develop a way to get information to the Rossi satellite so that it could quickly aim toward the burst and record information before the explosion's glow faded. Rossi pointed toward the burst and recorded data within four hours of the burst.
"We determined the burst location so precisely and so quickly that we had enough time to send information to other telescopes, like the Chandra X-ray Observatory," said Kippen. "These bigger observatories need more precise information and even more time to aim at a burst. Usually by the time we have enough data on a burst's location, it has already faded and can't be seen by other observatories."
NASA's space-based Chandra Observatory, managed by the Marshall Center, was able to swing into position and catch the fading embers of the burst four days after the explosion, providing data on X-rays released by the blast.
Other observatories in space and on the ground recorded the energy being released from the blast in the form of gamma rays, X-rays and visible and radio waves. Using a variety of spacecraft to record different signatures of visible and invisible energy will enable scientists to learn more about these mysterious explosions.
"It was an excellent opportunity for Chandra to make its first observation of a gamma-ray source," said Dr. Gerald Fishman, principal investigator for the Burst and Transient Source Experiment at the Marshall Center. "The coordinated effort shows the value of spacecraft and people working together to make exciting observations that could not be made by one single observatory."
The reward for the years of effort to obtain this set of complementary observations is the large volume of data obtained on the burst. One early result has been published in astronomical circulars, indicating the blast occurred more than 10 billion light years away - putting it, in terms of age, roughly 2 billion years after the "Big Bang." A light year is the distance light travels in one year. The Big Bang theory assumes that initially the universe existed as a single compact ball of matter that exploded, forming gaseous debris, which eventually condensed to form stars and galaxies.
Scientists expect to publish many more findings about this burst in journals. The burst -- which one astronomer nicknamed Beethoven because it fell on the anniversary of the composer's birth on Dec. 16, 1770 -- was one of the brightest ever recorded by BATSE. The burst's official name is GRB 991216.
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