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Sept.
10, 2008: Astronomers announced today that a remarkable
gamma-ray burst visible to the human eye earlier this year
came from an explosive stellar jet aimed almost directly at
Earth.
 Right:
Click
to view a streaming animation of the explosive stellar jet,
an artist's concept.
NASA's
Swift satellite detected the explosion - formally named GRB
080319B - at 2:13 a.m. EDT on March 19, 2008, and pinpointed
its position in the constellation Bootes. The gamma-ray burst
became bright enough to see even without a telescope. Observations
of the event by a global array of satellites and ground-based
observatories have since given scientists the most detailed
portrait of a burst ever recorded.
"Swift
was designed to find unusual bursts," said Swift principal
investigator Neil Gehrels at NASA's Goddard Space Flight Center
in Greenbelt, Md. "We really hit the jackpot with this
one."
In
a paper to appear in Thursday's issue of Nature, Judith Racusin
of Penn State University and a team of 92 coauthors report
on observations across the spectrum that began 30 minutes
before the explosion and followed its afterglow for months.
The team concludes the burst's extraordinary brightness arose
from a jet that shot material directly toward Earth at 99.99995
percent the speed of light.
Within
the next 15 seconds, the burst brightened enough to be visible
in a dark sky to human eyes. It briefly crested at a magnitude
of 5.3 on the astronomical brightness scale. Incredibly, the
dying star was 7.5 billion light-years away.
Telescopes
around the world already were studying the afterglow of another
burst when GRB 080319B exploded just 10 degrees away. TORTORA,
a robotic wide-field optical camera operated in Chile with
Russian-Italian collaboration, also caught the early light:
movie.
TORTORA's rapid imaging provided the most detailed look yet
at visible light associated with a burst's initial gamma-ray
blast.
Above:
GRB 080319B makes a brief appearance among the stars of Bootes
in a movie made by Pi of the Sky, a Polish group that monitors
the sky for afterglows and other short-lived phenomena. [More]
Immediately
after the blast, Swift's UltraViolet and Optical Telescope
and X-Ray Telescope indicated they were effectively blinded.
Racusin initially thought something was wrong with the telescopes.
Within minutes, however, as reports from other observers arrived,
it was clear this was a special event.
Gamma-ray
bursts are the most luminous explosions in the Universe. Most
occur when massive stars run out of nuclear fuel. As a star's
core collapses, it creates a black hole or neutron star that,
through processes not fully understood, drive powerful gas
jets outward. These jets actually punch through the collapsing
star, carrying matter and beaming radiation into space.
The
team believes the jet directed toward Earth contained an ultra-fast
component just 0.4 of a degree across. This core resided within
a slightly less energetic jet about 20 times wider.
Above:
A two-component jet model explains the timing and spectral
evolution of GRB 080319B. Credit: Nature/Judith Racusin. [larger
image]
"It's
this wide jet that Swift usually sees from other bursts,"
Racusin explained. In the case of GRB 080319B, the narrow
jet was seen as well, resulting in the burst's unusual brightness.
"Maybe every gamma-ray burst contains a narrow jet, too,
but astronomers miss them because we don't see them head-on."
Such
an alignment occurs by chance only about once a decade, so
GRB 080319B was a rare catch indeed.
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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Naked
Eye Gamma-ray Burst -- Science@NASA
Swift
is managed by Goddard. It was built and is being operated
in collaboration with Penn State, the Los Alamos National
Laboratory, and General Dynamics in the U.S.; the University
of Leicester and Mullard Space Sciences Laboratory in
the United Kingdom; Brera Observatory and the Italian
Space Agency in Italy; plus additional partners in Germany
and Japan.
At
the same moment Swift saw the burst on March 19th, the
Russian KONUS instrument on NASA's Wind satellite also
sensed the gamma rays and provided a wide view of their
spectral structure. A robotic wide-field optical camera
called "Pi of the Sky" in Chile simultaneously
captured the burst's first visible light. The system
is operated by institutions from Poland.
NASA's
Future: US
Space Exploration Policy
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