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NASA Science News for April 10, 2003

It's a Supernova

A bright explosion two billion light years away is the missing link
between supernovas and gamma ray bursts. 

April 10, 2003: Scientists have discovered that one of the brightest
gamma ray bursts on record is also a supernova. It's the first direct
evidence linking these two types of explosions, both triggered by the
death of a massive star. 

NASA's High-Energy Transient Explorer satellite (HETE) initially
detected the burst on March 29, 2003, in the constellation Leo. For
more than 30 seconds, the burst outshone the entire universe in gamma
rays. 

Two hours later, the explosion's optical afterglow remained a
trillion times more luminous than the Sun. Although the fireball was
about two billion light-years away, it was nevertheless bright enough
to be detected by small telescopes on Earth. Sky watchers in Japan,
for instance, had no trouble photographing the fading afterglow using
a 12" telescope at the Tokyo Institute of Technology. 

In Arizona, astronomers turned the Multiple Mirror Telescope (MMT) at
Mount Hopkins toward the gamma ray burst afterglow and soon spotted
the telltale signs of a supernova. Scientists cannot yet determine
which came first, the burst or the supernova, but the same event, a
star explosion, was certainly the trigger for both. 

"There should no longer be doubt in anybody's mind that gamma ray
bursts and supernovae are connected," said Thomas Matheson of the
Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, Mass.,
and a member of the team that made the discovery. Matheson's
colleagues include Peter Garnavich of Notre Dame and Krzysztof Stanek
of the CfA. 

Gamma ray bursts are the most powerful explosions in the universe,
and they likely signal the birth of black holes. Bursts occur at
random locations scattered across the sky. Few last more than a
minute, making them hard to study. 

A supernova is the explosion of a star at least eight times as
massive as the sun. When such stars deplete their nuclear fuel, they
no longer have the energy to support their mass. Their cores implode,
forming either a neutron star or, if there is enough mass, a black
hole. The surface layers of the star blast outward, forming the
colorful patterns typical of supernova remnants. 

Previous observations, particularly from NASA's Chandra X-ray
Observatory, have provided convincing indirect evidence of the gamma
ray burst/supernova connection. The Chandra Observatory detected iron
and other heavy elements, which are formed in supernovas, in the
vicinity of gamma ray bursts. 

But this latest burst has provided a direct link: light from the
afterglow itself exhibits the same patterns as light from a
supernova. Namely, the scientists see changes in light absorbed by
silicon and iron atoms, forged in the supernova, as the afterglow
slowly fades away. Matheson's team is continuing to observe and
analyze this unique burst. 

"Scores of observatories, and even more observers, are now studying
this event," said Don Kniffen, at NASA Headquarters in Washington. "
We've been searching for a direct link for decades, and we finally
got it," he said. 

"All gamma ray bursts may have associated supernovae that are too
faint to observe," Matheson said. The March 29 burst, named GRB
030329, was one of the closest to Earth. It was approximately two
billion light-years away, as opposed to other bursts located more
than 10 billion light-years away. Because the burst was both
relatively close to Earth and bright, the supernova was
detectable ... and the long-sought missing link was finally found. 

Credits & Contacts
Source: A NASA HQ press release
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Steve Roy

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