Douglas Isbell
Headquarters, Washington, DC           December 17, 1996
(Phone:  202/358-1753)

Jerry Berg
Marshall Space Flight Center, Huntsville, AL
(Phone: 205/544-0034)

RELEASE:  96-261

ASTRONOMERS DETECT NEVER BEFORE 
SEEN GAMMA-RAY MULTI-BURSTS 

     The much-debated mystery of the source and origins of 
high-energy bursts of gamma rays observed in all directions 
in distant space has been given a puzzling new twist with the 
detection by NASA astronomers of the first sequence of 
repeated bursts in one region. 

     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:

               http://www.ssl.msfc.nasa.gov

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