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For more information, contact:

Bill Steigerwald
Goddard Space Flight Center
Greenbelt, Md.
(Phone: 301 286 5017)

Palle Moller
European Southern Observatory
Garching, Germany
Phone: +49 89 3200-6246
pmoller@eso.org

Jens Hjorth
University of Copenhagen
jens@astro.ku.dk

Chryssa Kouveliotou
NASA Marshall Space Flight Center
Chryssa.Kouveliotou-1@nasa.gov

Stan Woosley
University of California, Santa Cruz
woosley@ucolick.org
831-459-2976

More about Gamma-ray bursts

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Caption for Animation 1 and Images 1 - 7:

A computer animation of a gamma-ray burst destroying a star. This blue Wolf-Rayet star -- containing about 10 solar masses worth of helium, oxygen and heavier elements -- has depleted its nuclear fuel. This has triggered a Type Ic supernova / gamma-ray burst event.

The core of the star has collapsed, without the star's outer part knowing. A black hole forms inside surrounded by a disk of accreting matter, and, within a few seconds, launched a jet of matter away from the black hole that ultimately made the gamma-ray burst.

Here we see the jet (white plume) breaking through the outer shell of the star, about nine seconds after its creation. The jet of matter, in conjunction with vigorous winds of newly forged radioactive nickel-56 blowing off the disk inside, shatters the star within seconds. This shattering represents the supernova event.

Credit: NASA / SkyWorks Digital

Caption for Animation 2 and Images 8 & 9:

A computer animation of a gamma-ray burst / supernova viewed from a distance.

This blue Wolf-Rayet star -- containing about 10 solar masses worth of helium, oxygen and heavier elements -- has depleted its nuclear fuel. This has triggered a Type Ic supernova / gamma-ray burst event.

Here we see a blinding flash of light as the shell of the star explodes. Over the course of many years, a supernova remnant emerges (as represented by the fiery reddish cloud of gas surrounding the newly formed central black hole or neutron star). A shock wave (represented by an egg-shaped shell) is created by the expanding gases.

Scientists say the gamma-ray burst detected on March 29, 2003, was associated with a hypernova, which is more energetic and expands more rapidly than a supernova does.

Credit: NASA / SkyWorks Digital

Caption for Animation 3:

This computer simulation shows the distribution of relativistic particles (moving near light speed) in the jet as it breaks out of the star. Yellow and orange are very high energy and will ultimately make a gamma-ray burst, but only for an observer looking along the jet (+/- about 5 degrees). Note also the presence of some small amount of energy in mildly relativistic matter (blue) at larger angles off the jet. These will produce X-ray flashes that may be much more frequently seen.

Credit: Weiqun Zhang and Stan Woosley

Caption for Image 10:

This image is from a computer simulation of the beginning of a gamma-ray burst. Here we see the jet 9 seconds after its creation at the center of a Wolf Rayet star by the newly formed, accreting black hole within. The jet is now just erupting through the surface of the Wolf Rayet star, which has a radius comparable to that of the sun. Blue represents regions of low mass concentration, red is denser, and yellow denser still. Note the blue and red striations behind the head of the jet. These are bounded by internal shocks.

Credit: Weiqun Zhang and Stan Woosley

(The calculation was carried out at the National Energy Research Scientific Computing Center at Lawrence Berkeley Laboratory and used about 25,000
processor hours.)

Caption for Image 11:

This image is from a computer computer simulation showing the distribution of relativistic particles (moving near light speed) in the jet as it breaks out of the star. Yellow and orange are very high energy and will ultimately make a gamma-ray burst, but only for an observer looking along the jet (+- about 5 degrees). Note also the presence of some small amount of energy in mildly relativistic matter (blue) at larger angles off the jet. These will produce X-ray flashes that may be much more frequently seen.

Credit: Weiqun Zhang and Stan Woosley

(The calculation was carried out at the National Energy Research Scientific Computing Center at Lawrence Berkeley Laboratory and used about 25,000
processor hours.)

Caption for Image 12:

:The afterglow of GRB 030329 (white dot in center of image), as detected on April 15, 2003, by the Advanced Camera for Surveys on the Hubble Space Telescope.

Credit: The European Space Agency / NASA / Andrew Fruchter (STScI), Andrew
Levan (Leicester Univ.), GOSH Collaboration

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June 18, 2003 - (date of web publication)

"ROSETTA STONE" FOUND TO DECODE THE MYSTERY OF GAMMA RAY BURSTS

 

animation of a gamma-ray burst destroying a star

Animation 1

Click image for a 10 meg Quick Time movie

Scientists have pieced together the key elements of a gamma-ray burst, from star death to dramatic black hole birth, thanks to a March 29, 2003 explosion considered the "Rosetta stone" of such bursts.

 

 

 

animation of a supernova

Animation 2

Click image for a 3 meg Quick Time movie

This telling March 29 burst in the constellation Leo, one of the brightest and closest on record, reveals for the first time that a gamma-ray burst and a supernova -- the two most energetic explosions known in the Universe -- occur essentially simultaneously, a quick and powerful one-two punch.

 

 

 

simulation of a gamma-ray burst

Animation 3

click image for a 6 meg MPEG movie

The results appear in the June 19 issue of Nature. The burst was detected by NASA's High-Energy Transient Explorer (HETE) and observed in detail with the European Southern Observatory's Very Large Telescope (VLT) at the Paranal Observatory in Chile.

 

 

 

a gamma-ray burst destroying a star

Image 1

 

"We've been waiting for this one for a long, long time," said Dr. Jens Hjorth, University of Copenhagen, lead author on one of three Nature letters. "The March 29 burst contains all the missing information. It was created through the core collapse of a massive star."


 

 

a gamma-ray burst destroying a star

Image 2

 

The team said that the Rosetta stone burst also provides a lower limit on how energetic gamma-ray bursts truly are and rules out most theories concerning the origin of "long bursts," lasting longer than two seconds.

 

 

 

a gamma-ray burst destroying a star

Image 3

 

Gamma-ray bursts temporarily outshine the entire Universe in gamma-ray light, packing the energy of over a million billion suns. Yet these explosions are fleeting -- lasting only seconds to minutes -- and occur randomly from all directions on the sky, making them difficult to study.

 

 

 

a gamma-ray burst destroying a star

Image 4

 

A supernova is associated with the death of a star about eight times as massive as the Sun or more. When such stars deplete their nuclear fuel, they no longer have the energy (in the form of radiation pressure outward) 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.

 

 

 

a gamma-ray burst destroying a star

Image 5

 

Scientists have suspected gamma-ray bursts and supernovae were related, but they have had little observational evidence, until March 29.

 

 

 

 

a gamma-ray burst destroying a star

Image 6

 

"The March 29 burst changes everything," said co-author Dr. Stan Woosley, University of California, Santa Cruz. Just as the Rosetta stone helped us understand a lost, ancient language, this burst will serve as a tool to decode gamma-ray bursts. It's now known for certain that at least some gamma-ray bursts are produced when black holes, or perhaps very unusual neutron stars, are born inside massive stars, according to the team.

 

 

 

a gamma-ray burst destroying a star

Image 7

 

GRB 030329, named after its detection date, occurred relatively close, approximately 2 billion light years away (at redshift 0.1685). The burst lasted over 30 seconds. ("Short bursts" are less than 2 seconds long.) GRB 030329 is among the 0.2% brightest bursts ever recorded. Its afterglow lingered for weeks in lower-energy X-ray and visible light.

 

 

 

A gamma-ray burst and supernova

Image 8

 

With the VLT, Hjorth and his colleagues uncovered evidence in the afterglow of a massive, rapidly expanding supernova shell, called a hypernova, at the same position and created at the same time as the afterglow. The following scenario emerged:

 

 

 

a supernova remnant

Image 9

 

Thousands of years prior to this explosion, a very massive star, running out of fuel, let loose much of its outer envelope, transforming itself into a bluish Wolf-Rayet star. The Wolf-Rayet star -- containing about 10 solar masses worth of helium, oxygen and heavier elements -- rapidly depleted its fuel, triggering the Type Ic supernova / gamma-ray burst event. The core collapsed, without the star's outer part knowing. A black hole formed inside surrounded by a disk of accreting matter, and, within a few seconds, launched a jet of matter away from the black hole that ultimately made the gamma-ray burst.

 

 

 

simulation of a gamma-ray burst

Image 10

 

The jet passed through the outer shell of the star and, in conjunction with vigorous winds of newly forged radioactive nickel-56 blowing off the disk inside, shattered the star. This shattering represents the supernova event. Meanwhile, collisions among pieces of the jet moving at different velocities, all very close to light speed, created the gamma-ray burst. This "collapsar" model, introduced by Woosley in 1993, best explains the observation of GRB 030329, as opposed to the "supranova" and "merging neutron star" models.

 

 

 

simulation of a gamma-ray burst

Image 11

 

In previous gamma-ray bursts, scientists had found evidence of iron in the afterglow light, a signature of a star explosion. Also, the location of a supernova occurring in 1998, named SN1998bw, appeared to be in the same vicinity as a gamma-ray burst. The data was inconclusive, however, and many scientists remained skeptical of the association.

 

 

 

Hubble Space Telescope picture of gamma-ray burst afterglow

Image 12

 

"Supernova 1998bw whetted our appetite," said co-author Dr. Chryssa Kouveliotou of the NASA Marshall Space Flight Center in Huntsville, Ala. "But it took five more years before we could confidently say we found the smoking gun that nailed the association between gamma-ray bursts and supernovae, at least for some bursts."

"This does not mean that the gamma-ray burst mystery is solved," Woosley said. "We are confident that long bursts involve a core collapse, probably creating a black hole. We have convinced most skeptics. We cannot reach any conclusion yet, however, on what causes short gamma-ray bursts."

Short bursts might be caused by neutron star mergers. A NASA-led international satellite named Swift, to be launched in January 2004, will "swiftly" locate gamma-ray bursts and may capture short-burst afterglows, which have yet to be detected.

The VLT is the world's most advanced optical telescope, comprising four 8.2-meter reflecting Unit Telescopes and, in the future, four moving 1.8-meter Auxiliary Telescopes for interferometry. HETE was built by MIT as a mission of opportunity under the NASA Explorer Program, with collaboration among U.S. universities, Los Alamos National Laboratory, and scientists and organizations in Brazil, France, India, Italy and Japan.

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