'Naked-Eye' Gamma-Ray Burst Was Aimed Squarely At Earth
- From: baalke@xxxxxxxxxxxxx
- Date: Wed, 10 Sep 2008 10:54:34 -0700 (PDT)
Sept. 10, 2008
J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@xxxxxxxx
Lynn Cominsky
Sonoma State University, Rohnert Park, Calif.
707-664-2655
lynnc@xxxxxxxxxxxxxxxxxxx
RELEASE: 08-223
"NAKED-EYE" GAMMA-RAY BURST WAS AIMED SQUARELY AT EARTH
WASHINGTON -- Data from satellites and observatories around the globe
show a jet from a powerful stellar explosion witnessed March 19 was
aimed almost directly at Earth.
NASA's Swift satellite detected the explosion - formally named GRB
080319B - at 2:13 a.m. EDT that morning and pinpointed its position
in the constellation Bootes. The event, called a gamma-ray burst,
became bright enough for human eyes to see. Observations of the event
are giving astronomers 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.
At the same moment Swift saw the burst, 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.
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. TORTORA's
rapid imaging provided the most detailed look yet at visible light
associated with a burst's initial gamma-ray blast.
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. Within minutes, however, as
reports from other observers arrived, it was clear this was a special
event.
Gamma-ray bursts are the universe's most luminous explosions. 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 punch through the collapsing star. As the jets shoot into
space, they strike gas previously shed by the star and heat it. That
generates bright afterglows.
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.
"It's this wide jet that Swift usually sees from other bursts,"
Racusin explained. "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 a GRB
080319B is a rare catch.
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.
For related images to this telecon, please visit:
http://www.nasa.gov/mission_pages/swift/bursts/naked_eye_telecon.html
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