NASA's Swift Catches Farthest-Ever Gamma-Ray Burst
- From: baalke@xxxxxxxxxxxxx
- Date: Fri, 19 Sep 2008 15:25:46 -0700 (PDT)
Sept. 19, 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: 08-239
NASA'S SWIFT CATCHES FARTHEST-EVER GAMMA-RAY BURST
WASHINGTON -- NASA's Swift satellite has found the most distant
gamma-ray burst ever detected. The blast, designated GRB 080913,
arose from an exploding star 12.8 billion light-years away.
"This is the most amazing burst Swift has seen," said the mission's
lead scientist Neil Gehrels at NASA's Goddard Space Flight Center in
Greenbelt, Md. "It's coming to us from near the edge of the visible
universe."
Because light moves at finite speed, looking farther into the
universe
means looking back in time. GRB 080913's "lookback time" reveals that
the burst occurred less than 825 million years after the universe
began.
The star that caused this "shot seen across the cosmos" died when the
universe was less than one-seventh its present age. "This burst
accompanies the death of a star from one of the universe's early
generations," says Patricia Schady of the Mullard Space Science
Laboratory at University College London, who is organizing Swift
observations of the event.
Gamma rays from the far-off explosion triggered Swift's Burst Alert
Telescope at 1:47 a.m. EDT on Sept. 13. The spacecraft established
the event's location in the constellation Eridanus and quickly turned
to examine the spot. Less than two minutes after the alert, Swift's
X-Ray Telescope began observing the position. There, it found a
fading, previously unknown X-ray source.
Astronomers on the ground followed up as well. Using a 2.2-meter
telescope at the European Southern Observatory in La Silla, Chile, a
group led by Jochen Greiner at the Max Planck Institute for
Extraterrestrial Physics in Garching, Germany, captured the bursts
fading afterglow.
The telescope's software listens for alerts from Swift and
automatically slewed to the burst position. Then, the team's
Gamma-Ray Burst Optical/Near-Infrared Detector, or GROND,
simultaneously captured the waning light in seven wavelengths. "Our
first exposure began just one minute after the X-Ray Telescope
started observing," Greiner says.
In certain colors, the brightness of a distant object shows a
characteristic drop caused by intervening gas clouds. The farther
away the object is, the longer the wavelength where this fade-out
begins. GROND exploits this effect and gives astronomers a quick
estimate of an explosion's shift toward the less energetic red end of
the electromagnetic spectrum, or "redshift," which suggests its
record-setting distance.
An hour and a half later, as part of Greiner's research, the Very
Large Telescope at Paranal, Chile, targeted the afterglow. Analysis
of the spectrum with Johan Fynbo of the University of Copenhagen
established the blasts redshift at 6.7 -- among the most distant
objects known.
Gamma-ray bursts are the universe's most luminous explosions. Most
occur when massive stars run out of nuclear fuel. As their cores
collapse into a black hole or neutron star, gas jets -- driven by
processes not fully understood -- punch through the star and blast
into space. There, they strike gas previously shed by the star and
heat it, which generates bright afterglows.
The previous record holder was a burst with a redshift of 6.29, which
placed it 70 million light-years closer than GRB 080913.
Swift, launched in November 2004, has had a banner year. In March,
the
satellite detected the brightest gamma-ray burst, which was visible
to the human eye despite occurring billions of light-years away. And
in January, the spacecraft's instruments caught the first X-rays from
a new supernova days before optical astronomers saw the exploding
star.
Swift is managed by Goddard. It was built and is being operated in
collaboration with Penn State University, University Park, Pa., the
Los Alamos National Laboratory in New Mexico, and General Dynamics of
Gilbert, Ariz., in the U.S. International collaborators include the
University of Leicester and Mullard Space Sciences Laboratory in the
United Kingdom, Brera Observatory and the Italian Space Agency in
Italy, and additional partners in Germany and Japan.
For related images to this release, please visit:
http://www.nasa.gov/mission_pages/swift/bursts/farthest_grb.html
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