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For more information contact:

Nancy Neal
Headquarters, Washington, DC
(Phone: 202-358-2369)

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

Gamma Ray Burst Primer, History and Glossary (PDF format)

HETE website

Viewable Images

Caption for Animation "Death Cry" and Animation Still images 1 - 7 found at the bottom of this page:
Part 1 (Image 1) -- A Wolf-Rayet star in its final hours. Wolf-Rayet stars are extremely massive bluish stars, containing the mass of 10 to 15 suns. The blue-white color of the star indicates that its surface temperature is approximately 50,000 C. Surrounding the star are wisps of gas that have recently been shed from the outer atmosphere.

Part 2 (Images 2-4) -- Diving through the surface of the Wolf-Rayet star, we come to the stellar core, about 10 percent the size of the whole star. We see shells of iron, oxygen, and carbon in the core, the ash of nuclear burning. This star is now out of fuel. Lacking energy to support its own mass, the core collapses and a black hole forms, pulling in matter. Yet a jet of material escapes through the polar regions, perhaps powered by renewed fusion and the spin of the black hole. The animation is nearly in real-time.

Part 3 -- (Image 5) The jet of material formed in the stellar core pierces through the star's surface, traveling at near light speed.

Part 4 -- (Images 6 and 7) The Wolf-Rayet star and its newly-formed jets from a more distant perspective. We see that internal collisions of the jet material with itself are releasing energy -- photons that will eventually be observed as gamma-rays by satellites in Earth orbit when the beam is pointed in our direction.

Credit: NASA/Dana Berry/SkyWorks Digital

For HIGH RESOLUTIONS of the animation stills, click on link BELOW each picture. To EXPAND size of image, click ON the image itself. These images are found at the BOTTOM of this page.

Caption for Animation "Network": HETE-2 ANIMATION - HETE-2 will be launched from the Kwajalein Atoll in the Pacific Ocean and once in orbit, will keep an eye open and search the Universe for powerful, mysterious cosmic explosions calls gamma ray bursts (GRBs). HETE's technology will detect the GRBs and then immediately distribute their astronomical coordinates to interested ground-based observers making it possible to view and collect data on the brief phenomenon. Credit: NASA/Dana Berry/SkyWorks Digital

Caption for Gamma Ray Burst in the Sky Animation: Gamma ray bursts (GRBs) occur several times a day without warning and release more energy than any event in the Universe. Credit: NASA

Caption for Image Eta Carinae: Eta Carinae is the most luminous star known in our galaxy. It radiates energy at a rate that is 5 million times that of the sun. Observations indicate that Eta Carinae is an unstable star that is rapidly boiling matter off its surface. Some astronomers think that it could explode as a supernova any time! At a distance of 7,000 light years from Earth, this gigantic explosion would pose no threat to life but it would be quite a show. Credit: NASA/CXC/SAO Click here for high resolution image.

Caption for Burst Simulation Animation: 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
(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 Lightcurves: The early-time lightcurves of three gamma-ray bursts that were observed within minutes of the burst. GRB990123 and GRB021211 experienced a fast decay at early times (power law index alpha ~ -2), which later flattened out to a typical late-time decay of index alpha ~ -1. By contrast, the early decay of GRB021004 was much slower (index alpha ~ -0.5); steepening to the typical late-time value only after more than 2 hours. This slow decay must have been powered by continued energy input to the shock region of the gamma-ray burst. Credit: Derek Fox, Caltech
High Resolution image

Caption for the HETE Burst Alert Network: HETE circles the globe along the equator every 96 minutes, transmitting alerts and sky locations for the gamma-ray bursts (GRBs) that it detects. The alerts are transmitted in turn to each of fourteen automated VHF receivers along its track as they come within range. The ground receivers are inexpensive ham radio units, dedicated to receiving HETE signals. They are connected to the Internet for re-sending of alerts to MIT and subsequently to the GCN. For GRB021004 and GRB021211, the first alerts went to the Kwajalein and Galapagos stations, respectively. Credit: George Ricker, MIT


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March 19, 2003 - (date of web publication)



Death Cry


Scientists arriving on the scene of a gamma-ray burst just moments after the explosion, have witnessed the death of a gigantic star and the birth of something monstrous in its place, quite possibly a brand new, spinning black hole.

The burst observation, featured in the March 20 issue of Nature, is the most detailed to date. The observation confirms that gamma-ray bursts announce the demise of the most massive stars in the universe, a theory called the collapsar model. NASA's High-Energy Transient Explorer (HETE), ground-based robotic telescopes, and fast-thinking researchers around the globe, made the prompt observation possible.




"This stunning observation places us in the fiery throes of a star explosion, peering through the debris at a newly formed black hole within," said Dr. Anne Kinney, NASA director for astronomy and physics, Headquarters, Washington.

"If a gamma-ray burst is the birth cry of a black hole, then the HETE satellite has just allowed us into the delivery room," said Dr. Derek Fox of the California Institute of Technology in Pasadena, Calif., the lead author of the Nature paper.

Gamma-ray bursts shine hundreds of times brighter than a supernova, or as bright as a million trillion suns. The mysterious bursts are common, yet random and fleeting. The gamma-ray portion of a burst typically lasts from a few milliseconds to 100 seconds. An afterglow, caused by shock waves from the explosion sweeping up matter and ramming this into the region around the burst, can linger for days or weeks in lower-energy forms of light, such as X rays or visible light.


Gamma Ray Burst in the Sky Animation


A gamma-ray burst, named GRB021004, appeared on October 4, 2002, at 8:06 a.m. EDT. Wasting no time, HETE spotted the burst, nailed down a location, and notified observers worldwide within a few seconds, while the gamma rays were still pouring in. First on the scene was the Automated Response Telescope (ART) in Wako, Japan, observing the region just 193 seconds after the burst.

Fox pinpointed the afterglow shortly after this from images captured by a telescope on Mt. Palomar, near San Diego. Then the race was on, as scientists, using more than 50 telescopes, in California, across the Pacific, Australia, Asia, and Europe zoomed in on the afterglow before the approaching sunrise.


Eta Carinae


Scientists arrived on the scene of GRB021004 early enough to witness an entirely new phenomenon: the ongoing energizing of the burst afterglow for more than half an hour after the burst. This power must have been provided by whatever object produced the gamma-ray burst itself.

"Gamma-ray bursts must be many times more times powerful than we previously thought," said Dr. George Ricker of the Massachusetts Institute of Technology (MIT), Cambridge, Mass., principal investigator for the HETE mission. "The gamma-ray portion of the burst is perhaps just the tip of the iceberg," he said.


Burst simulation animation

Click on image above to start animation.

These findings support the collapsar model, where the core of a massive star collapses into a black hole. The black hole's spin or magnetic fields may be acting like a slingshot, flinging material into the surrounding debris. Scientists calculated that GRB021004 originated from a star 15 times more massive than the Earth's sun.

Gamma-ray burst hunters are greatly aided by three new developments: fast triggers from orbiting detectors; fast relays to observers worldwide via the Gamma-ray burst Coordinates Network; and fast responses from ground-based robotic telescopes. HETE is the first satellite to provide and distribute accurate burst locations within seconds. In December 2003, NASA will launch the Swift satellite, which will have an even greater capability to detect and locate bursts, as well as onboard optical, ultraviolet and X-ray telescopes.




Fox and his colleagues relied on data from ART in Japan, the Palomar Oschin Telescope and the Near Earth Asteroid Tracking camera, which are automated. HETE was built by MIT as a mission of opportunity under the NASA Explorer Program, collaboration among U.S. universities, Los Alamos National Laboratory, and scientists and organizations in Brazil, France, India, Italy and Japan.


HETE Burst Alert Network

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Animation stills below (click link BELOW each pic for a HIGH RESOLUTION of the image--Click ON the image for a LARGER VIEW of image). Stills are in clockwise order.



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