Caltech News Release<br />Embargoed for Release at 11 a.m. PST, Wednesday, March 19, 2003<br /><br />Quick action by astronomers worldwide leads<br />to new insights on mysterious gamma-ray bursts<br /><br />PASADENA, Calif.-Scientists "arriving quickly on the scene" of an <br />October 4 gamma-ray burst have announced that their rapid <br />accumulation of data has provided new insights about this exotic <br />astrophysical phenomenon. The researchers have seen, for the first <br />time, ongoing energizing of the burst afterglow for more than half an <br />hour after the initial explosion.<br /><br />The findings support the "collapsar" model, in which the core of a <br />star 15 times more massive than the sun collapses into a black hole. <br />The black hole's spin, or magnetic fields, may be acting like a <br />slingshot, flinging material into the surrounding debris.<br /><br />The prompt observation-and by far the most detailed to date-was made <br />possible by several ground- and space-based observatories operating <br />in tandem. The blast was initially detected by NASA's High-Energy <br />Transient Explorer (HETE) satellite, and follow-up observations were <br />quickly undertaken using ground-based robotic telescopes and <br />fast-thinking researchers around the globe. The results are reported <br />in the March 20<br />issue of the journal Nature.<br /><br />"If a gamma-ray burst is the birth cry of a black hole, then the HETE <br />satellite has just allowed us into the delivery room," said Derek <br />Fox, a postdoctoral researcher at the California Institute of <br />Technology and lead author of the Nature paper. Fox discovered the<br />afterglow, or glowing embers of the burst, using the Oschin 48-inch <br />telescope located at Caltech's Palomar Observatory.<br /><br />Gamma-ray bursts shine hundreds of times brighter than a supernova, <br />or as bright as a million trillion suns. The mysterious bursts are <br />common, yet random and fleeting. The gamma-ray portion of a burst <br />typically lasts from a few milliseconds to a couple of minutes. An <br />afterglow, caused by shock waves from the explosion sweeping up matter<br />and ramming it into the region around the burst, can linger for much <br />longer, releasing energy in X rays, visible light, and radio waves.<br />It is from the studies of such afterglows that astronomers can hope <br />to learn more about the origins and nature of these extreme cosmic <br />explosions.<br /><br />This gamma-ray burst, called GRB021004, appeared on October 4, 2002, <br />at 8:06 a.m. EDT. Seconds after HETE detected the burst, an e-mail <br />providing accurate coordinates was sent to observatories around the <br />world, including Caltech's Palomar Observatory. Fox pinpointed the <br />afterglow shortly afterward from images captured by the Oschin <br />Telescope<br />within minutes of the burst, and notified the astronomical community <br />through a rapid e-mail system operated by NASA for the follow-up <br />studies of gamma-ray bursts. Then the race was on, as scientists in <br />California, across the Pacific, Australia, Asia, and Europe employed<br />more than 50 telescopes to zoom in on the afterglow before the <br />approaching sunrise.<br /><br />At about the same time, the afterglow was detected by the Automated <br />Response Telescope (ART) in Japan, a 20-centimeter instrument located <br />in Wako, a Tokyo suburb, and operated by the Japanese research <br />institute RIKEN. The ART started observing the region a mere 193 <br />seconds after the burst, but it took a few days for these essential <br />observations to be<br />properly analyzed and distributed to the astronomical community.<br /><br />Analysis of these rapid observations produced a surprise: <br />fluctuations in brightness, which scientists interpreted as the <br />evidence for a continued injection of energy into the afterglow, well <br />after the burst occurred. According to Shri Kulkarni, who is the <br />McArthur Professor<br />of Astronomy and Planetary Science at Caltech, the newly observed <br />energizing of the burst afterglow indicates that the power must have <br />been provided by whatever object produced the gamma-ray burst itself.<br /><br />"This ongoing energy shows that the explosion is not a simple, <br />one-time event, but that the central source lives for a longer time," <br />said Kulkarni, a co-author of the Nature paper. "This is bringing <br />us closer to a full understanding of these remarkable cosmic flashes."<br /><br />Added Fox, "In the past we used to be impressed by the energy release <br />in gamma-rays alone. These explosions appear to be more energetic <br />than meets the eye."<br /><br />Later radio observations undertaken at the Very Large Array in New <br />Mexico and other radio telescopes, including Caltech's Owens Valley <br />Radio Observatory and the IRAM millimeter telescope in France, lend <br />further support to the idea that the explosions continued increasing <br />in energy. "Whatever monster created this burst just refused to die <br />quietly," said D. A. Frail, co-author and a staff astronomer at the <br />Very Large Array.<br /><br />Fox and his colleagues relied on data from the RIKEN telescope, in <br />Japan, and from the Palomar Oschin Telescope and its Near Earth <br />Asteroid Tracking (NEAT) camera, an instrument that has been <br />roboticized and is currently managed by a team of astronomers at JPL <br />led by Steven Pravdo. The collaboration of the Caltech astronomers <br />and the NEAT<br />team has proven extremely fruitful for the global astronomical <br />community, helping to identify fully 25 percent of the afterglows <br />discovered worldwide since Fox retrofitted the<br />telescope software for this new task in the autumn of 2001.<br /><br />HETE is the first satellite to provide and distribute accurate burst <br />locations within<br />seconds. The principal investigator for the HETE satellite is George <br />Ricker of the Massachussetts Institute of Technology. HETE was built <br />as a "mission of opportunity" under the NASA Explorer Program, a <br />collaboration among U.S. universities, Los Alamos<br />National Laboratory, and scientists and organizations in Brazil, <br />France, India, Italy, and Japan.<br /><br />###<br /><br /><br />Editors: NASA will host a major press conference at 2 pm EST, <br />Wednesday, March 19, at NASA Headquarters, Washington DC. Further <br />details, including images and animation, can be found at <br />http://www.gsfc.nasa.gov/topost/20030224blackhole.html<br /><br />Further details of the Nature paper can be found at http://www.nature.com.<br /><br />Contact: Robert Tindol<br />(626) 395-3631<br />tindol@caltech.edu