December 17, 1996
Four separate gamma-ray bursts were detected in two groups of two in rapid succession on October 27 and October 29, respectively. Astronomers based at NASA's Marshall Space Flight Center in Huntsville, AL, measured the unique sequence using the Burst and Transient Source Experiment (BATSE) instrument aboard NASA's Earth-orbiting Compton Gamma Ray Observatory, launched from the Space Shuttle Atlantis in April 1991. The repeated bursts are unlike any of the other 1,700 gamma-ray bursts observed by BATSE.
Marshall Space Sciences Laboratory astrophysicist Dr. Valerie Connaughton will present more details on the findings in a paper at the Texas Symposium on Relativistic Astrophysics in Chicago on Wednesday, December 18, at 4:15 p.m. CST at the Palmer House Hilton.
The BATSE finding is expected to prompt vigorous debate on subjects such as the distance to the sources of gamma-ray bursts and their causes -- subjects still debated by scientists despite nearly 25 years of study.
BATSE usually detects only about one gamma-ray burst per day, lasting from 10-30 seconds, and the locations of these events on the sky appear to be randomly distributed. "That's what makes these recent events so unusual," said Dr. Charles Meegan, BATSE experiment co-investigator. "They came right after one another, about two days apart, and all from the same part of the sky. Moreover, the last one was much longer than usual, lasting 23 minutes."
The BATSE astronomers cannot yet say for sure whether these events were produced by just one object in space, or several, but "it would be unlikely that this actually happened by chance" in four unrelated places, said Connaughton.
"Some astronomers argue for an explanation that the origin of these bursts is fairly local, just outside our own galaxy," said Dr. Gerald Fishman, BATSE principal investigator, who agrees that the recent events are likely related. "But most believe that bursts come from remote parts of the universe, at cosmological distances of a billion light years or more."
Another debated topic is how bursts are created. One theory suggests that bursts do not repeat from the same source because they involve a tremendous explosion that destroys the source in the process. Another possibility is that bursts occur when neutron stars merge, which would not be consistent with repeating bursts. "This discovery of multiple bursts adds fuel to the debate as to the source of the bursts," said Fishman.
The discovery was confirmed by three other gamma-ray burst detectors. Scientists from NASA's Goddard Space Flight Center in Greenbelt, MD, the University of California at Berkeley and the Ioffe Institute in Russia participated in the discovery.
The Texas Symposium on Relativistic Astrophysics is one of the most significant scientific forums for high energy astrophysics, and is being attended by leading astronomers from around the world, including Sir Martin Rees from Cambridge University. Dr. Rees is scheduled to present an invited talk on gamma-ray bursts at the meeting today.
Press contacts during the symposium are Don Sena of the Fermi National Accelerator Laboratory and Diana Steele of the University of Chicago, who can be reached at 312/917-1781, fax 312/917-1786. To arrange an interview with a NASA BATSE researcher at the symposium, Kelly McFalls of the Marshall Office of Public Affairs can be reached at that number.
The Burst and Transient Source Experiment is one of several instruments on NASA's Compton Gamma Ray Observatory. Other BATSE discoveries include a bursting pulsar, gamma rays from thunderstorms and eight new pulsars, and the observation of more than 1,700 gamma-ray bursts.
Further information on the mission and its accomplishments is available on the Internet home page of Marshall's Space Sciences Laboratory on the World Wide Web at URL:
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