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.
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