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Steve Roy
Media Relations Dept.
Marshall Space Flight Center, Huntsville, AL
steve.roy{at}msfc.nasa.gov
(256) 544-0034

Megan Watzke
Chandra X-ray Obs. Center, CFA, Cambridge, MA
cxcpress{at}cfa.harvard.edu
(617) 496-7998

Science Contacts:

Nathaniel Butler, nrbutler{at}mit.edu, 617-253-9687
George Ricker, grr{at}space.mit.edu

For release: 03/24/03

Release No.: 03-041

Cosmic forensics confirms gamma-ray burst and supernova
connection

Scientists announced today that they have used NASA's
Chandra X-ray Observatory to confirm that a gamma-ray
burst was connected to the death of a massive star. This
result is an important step in understanding the origin
of gamma-ray bursts, the most violent events in the
present-day Universe.

"If a gamma-ray burst were a crime, then we now have
strong circumstantial evidence that a supernova
explosion was at the scene," said Nathaniel Butler of
Massachusetts Institute of Technology in Cambridge,
lead author of a paper presented today at the meeting
of the High Energy Division of the American Astronomical
Society.

Chandra was able to obtain an unusually long observation
(approximately 21 hours) of the afterglow of GRB 020813
(so named because the High-Energy Transient Explorer,
HETE, discovered it on August 13, 2002.)  A grating
spectrometer aboard Chandra revealed an overabundance
of elements characteristically dispersed in a supernova
explosion.  Narrow lines, or bumps, due to silicon and
sulfur ions (atoms stripped of most of their electrons)
were clearly identified in the X-ray spectrum of
GRB 020813.

"Our observation of GRB 020813 supports two of the most
important features of the popular supra-nova model for
gamma-ray bursts," said Butler. "An extremely massive
star likely exploded less than two months prior to the
gamma-ray burst, and the radiation from the gamma-ray
burst was beamed into a narrow cone."

An analysis of the data showed that the ions were
moving away from the site of the gamma-ray burst at a
tenth the speed of light, probably as part of a shell
of matter ejected in the supernova explosion. The
line features were observed to be sharply peaked,
indicating that they were coming from a narrow region
of the expanding shell. This implies that only a small
fraction of the shell was illuminated by the gamma-ray
burst, as would be expected if the burst was beamed
into a narrow cone. The observed duration of the
afterglow suggests a delay of about 60 days between
the supernova and the gamma ray burst.

The supra-nova model involves a two-step process: the
first step is the collapse of the core of an extremely
massive star accompanied by the ejection of the outer
layers of the star. The collapsed core forms a rapidly
rotating black hole surrounded by a swirling disk of
matter. In the second step this black hole-disk system
produces a jet of high-energy particles. Shock waves
within the jet produce the burst of X-rays and gamma
rays that is observed to last only a few minutes.
Interaction of the jet with the ejected supernova shell
produces the X-ray afterglow, which can last for days
or even months. The reason for the delay between the
formation of the black hole and the production of the
jet is not understood.

Earlier observations with Japan's ASCA, the Italian-
Netherlands Beppo-SAX, and the European Space Agency's
XMM-Newton satellites, as well as Chandra had given
some indication of the presence of elements expected
in a shell ejected by a supernova. However, the number
of X-rays detected in those observations was small,
and the possibility remained that the reported lines
were an instrumental effect or statistical fluctuation.
Since Chandra was able to observe X-ray lines from
GRB 020813 for almost an entire day, the number of
X-rays detected was five times larger than for
previous observations. This enabled the team to make
a definitive identification of the silicon and sulfur
lines.

Chandra observed GRB 020813 for about 77,000 seconds,
approximately 21 hours after the initial burst. Other
members of the research team included Herman Marshall,
George Ricker, Roland Vanderspeak, Peter Ford, Geoffrey
Crew (MIT), and Donald Lamb (University of Chicago).

The High Energy Transmission Grating Spectrometer was
built by MIT. NASA's Marshall Space Flight Center in
Huntsville, Ala., manages the Chandra program, and TRW,
Inc., Redondo Beach, Calif., is the prime contractor
for the spacecraft. The Smithsonian's Chandra X-ray
Center controls science and flight operations from
Cambridge, Mass., for the Office of Space Science at
NASA Headquarters, Washington.

Images and additional information about this result are
available at:

     http://chandra.harvard.edu

and

     http://chandra.nasa.gov

Note: From March 23-26, 2003, the principal investigators
in this research will be attending the High Energy
Astrophysics Division meeting in Mt. Tremblant,
Canada. To reach the Press Room of this event, call
(819) 681-4200.

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