SCIENTISTS WORLDWIDE RACE TO OBSERVE FADING GAMMA-RAY BURST

Dolores Beasley
Headquarters, Washington                     October 8, 2002
(Phone: 202/358-1753)

Nancy Neal
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-0045)

RELEASE: 02-196

SCIENTISTS WORLDWIDE RACE TO OBSERVE FADING GAMMA-RAY BURST

     Scientists have seen the afterglow of a gamma-ray burst 
just nine minutes after the explosion, a result of precision 
coordination and fast slewing of ground-based telescopes 
upon detection of the burst by NASA's High-Energy Transient 
Explorer (HETE) satellite.

The quick turnaround has so far allowed scientists to 
determine a minimum distance to the explosion, which likely 
marks the creation of a black hole. Results continue to pour 
in, as nearly 100 telescopes in 11 countries have tracked 
the burst. 

The burst was detected on Friday, Oct. 4, at 8:06 a.m. EDT. 
NASA's Hubble Space Telescope and Chandra X-ray Observatory 
observed the afterglow on the following day, and another 
Hubble observation is planned for later this week. These and 
other observations are providing valuable clues to the 
mysterious nature of gamma-ray bursts, the most powerful 
explosions known. 

"This is the big one that didn't get away," said George R. 
Ricker of the Massachusetts Institute of Technology in 
Cambridge, principal investigator for the international 20-
person HETE team. "HETE sent out a burst alert in 11 seconds 
and then followed-up with an accurate location just 48 
seconds later, while the bright gamma-ray emission was still 
in progress. HETE's prompt localization has resulted in this 
burst being by far the best-observed burst in the 30-year 
history of gamma-ray burst astronomy."

The burst lasted approximately 100 seconds, a relatively 
bright and long-lasting burst. Racing the clock and the 
break of dawn, Derek Fox, an astronomer at California 
Institute of Technology in Pasadena, turned the 48-inch 
Oschin Schmidt telescope at the Palomar Observatory to the 
location that HETE provided. Just nine minutes after the 
burst, Fox detected a fading, 15th-magnitude source -- the 
afterglow of the burst. 

Gamma-ray bursts have the energy of a billion trillion Suns. 
Scientists have been hard-pressed to determine their origin, 
because they occur randomly in the universe and disappear 
quickly, usually within a minute or less.  Theorists say the 
bursts are the creation of a black hole as a result of 
massive star explosions or the merger of neutron stars, or 
both. 

HETE is designed to detect gamma-ray bursts and relay their 
locations within seconds to a worldwide network of radio, 
optical and X-ray telescopes. While the burst itself -- a 
flash of gamma rays, the most energetic form of light -- 
disappears quickly, the afterglow may linger in lower-energy 
light forms for days or weeks. 

The optical afterglow of this burst is still so bright that 
it outshines the entire galaxy in which it is located, 
making it too bright to obtain information about its host 
galaxy for now.

Japanese astronomers in Kyoto and Bisei, under a blanket of 
dark sky, confirmed the Palomar observation and watched the 
burst's brightness fade by half over the next two hours. 
Seven hours after the burst occurred, astronomers at the 
Siding Spring Observatory in Australia reported the burst 
occurred more than 10 billion light-years from Earth. 

By Saturday, amateur astronomers were also observing the 
spectacle. And in the hours and days to come, astronomers 
will comb the burst region with radio, X-ray and other 
optical telescopes, searching for more clues to the burst's 
origin.

HETE, a U.S. collaboration with France and Japan, is the 
first satellite dedicated to the study of gamma-ray bursts 
and is on an extended mission until 2004. NASA's Swift 
mission, planned for an October 2003 launch, is expected to 
detect, locate and observe bursts with even greater 
precision. 

For images and additional contact information, refer to:


http://www.gsfc.nasa.gov/topstory/20021008heteburst.html


-end-


More information on HETE can be found at: 
         http://space.mit.edu/HETE