Feb. 19, 2009

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington{at}nasa.gov

David Harris
SLAC National Accelerator Laboratory, Menlo Park, Calif.
650-926-8580
david.harris{at}slac.stanford.edu

Lynn Cominsky
Sonoma State University, Rohnert Park, Calif.
707-664-2655
lynnc{at}universe.sonoma.edu

RELEASE: 09-033

NASA'S FERMI TELESCOPE SEES MOST EXTREME GAMMA-RAY BLAST YET

WASHINGTON -- The first gamma-ray burst to be seen in high-resolution
from NASA's Fermi Gamma-ray Space Telescope is one for the record
books. The blast had the greatest total energy, the fastest motions
and the highest-energy initial emissions ever seen.

"We were waiting for this one," said Peter Michelson, the principal
investigator on Fermi's Large Area Telescope at Stanford University.
"Burst emissions at these energies are still poorly understood, and
Fermi is giving us the tools to understand them."

Gamma-ray bursts are the universe's most luminous explosions.
Astronomers believe most occur when exotic massive stars run out of
nuclear fuel. As a star's core collapses into a black hole, jets of
material -- powered by processes not yet fully understood -- blast
outward at nearly the speed of light. The jets bore all the way
through the collapsing star and continue into space, where they
interact with gas previously shed by the star and generate bright
afterglows that fade with time.

This explosion, designated GRB 080916C, occurred at 7:13 p.m. EDT on
Sept. 15, in the constellation Carina. Fermi's other instrument, the
Gamma-ray Burst Monitor, simultaneously recorded the event. Together,
the two instruments provide a view of the blast's initial, or prompt,
gamma-ray emission from energies between 3,000 to more than 5 billion
times that of visible light.

Nearly 32 hours after the blast, Jochen Greiner of the Max Planck
Institute for Extraterrestrial Physics in Garching, Germany, led a
group that searched for the explosion's fading afterglow. The team
simultaneously captured the field in seven wavelengths using the
Gamma-Ray Burst Optical/Near-Infrared Detector, or GROND, on the
2.2-meter telescope at the European Southern Observatory in La Silla,
Chile. In certain colors, the brightness of a distant object shows a
characteristic drop-off caused by intervening gas clouds. The farther
away the object is, the redder the wavelength where this fade-out
occurs. This gives astronomers a quick estimate of the object's
distance. The team's follow-up observations established that the
explosion took place 12.2 billion light-years away.

"Already, this was an exciting burst," said Julie McEnery, a Fermi
deputy project scientist at NASA's Goddard Space Flight Center in
Greenbelt, Md. "But with the GROND team's distance, it went from
exciting to extraordinary."

With the distance in hand, Fermi team members showed that the blast
exceeded the power of approximately 9,000 ordinary supernovae, if the
energy was emitted equally in all directions. This is a standard way
for astronomers to compare events even though gamma-ray bursts emit
most of their energy in tight jets.

Coupled with the Fermi measurements, the distance also helps
astronomers determine the slowest speeds possible for material
emitting the prompt gamma rays. Within the jet of this burst, gas
bullets must have moved at 99.9999 percent the speed of light. This
burst's tremendous power and speed make it the most extreme recorded
to date.

One curious aspect of the burst is a five-second delay separating the
highest-energy emissions from the lowest. Such a time lag has been
seen clearly in only one earlier burst.

"It may mean that the highest-energy emissions are coming from
different parts of the jet or created through a different mechanism,"
Michelson said.

The team's results appear today in the online edition of the journal
Science.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and
particle
physics partnership mission, developed in collaboration with the U.S.
Department of Energy and important contributions from academic
institutions and partners in France, Germany, Italy, Japan, Sweden,
and the U.S.

For images related to this release, visit:

http://www.nasa.gov/mission_pages/GLAST/news/high_grb.html

For more information about the Fermi Gamma-ray Space Telescope,
visit:

http://www.nasa.gov/fermi

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