PMO ASTRONOMER PROPOSED A MODEL FOR THE “NAKED-EYE” GAMMA-RAY BURST

　NASA's Swift satellite and the Russian KONUS detector on NASA's Wind satellite detected the explosion -- formally called GRB 080319B -- on March 19 at 2:13 a.m. U.S. Eastern Time that morning and pinpointed its position in the constellation Bo？tes. Simultaneously, a robotic wide-field optical camera called "Pi of the Sky" in Chile captured the burst's first visible light. Within the next 15 seconds, the blast became visible in a dark sky to human eyes. It briefly crested at magnitude 5.3 on the astronomical brightness scale. Incredibly, the dying star was 7.5 billion light-years away.

　 In a paper appeared in 2008 September 11's issue of Nature, Judith Racusin, and a team of 92 coauthors, report observations across the electromagnetic spectrum that began 30 minutes before the explosion and followed its afterglow for months. The team's observations give astronomers the most detailed portrait of a gamma-ray burst ever made.

　Gamma-ray bursts are the universe's most luminous explosions. Most occur when massive stars run out of nuclear fuel. As a star's core collapses, it creates a black hole or neutron star that, through processes not fully understood, drive powerful gas jets outward. These jets punch through the collapsing star. As the jets shoot into space, they strike gas previously shed by the star and heat it, which generates bright afterglows.

　In this Nature’s article, Xuefeng Wu, an associate research professor at Purple Mountain Observatory and a visiting scholar at Penn State University, leaded the Swift theory team including his colleagues at Penn State University and University of Nevada at Las Vegas (Judith Racusin, David Burrows, Peter Meszaros, and Bing Zhang) to propose a theoretical model to interpret this unusual event. According to their theory, the GRB has two jet components beaming towards the earth at 99.99995 percent the speed of light. The core component was only 0.4 degree across, but was very bright and moved ultra-fast. It resided within a slightly less energetic jet about 20 times wider. The broad component is more typical of what Swift sees from other bursts. Perhaps every gamma-ray burst has a narrow jet, but astronomers miss it most of the time. The nearly head-on alignment required to see it occurs by chance only about once a decade.

　Swift is managed by NASA's Goddard Space Flight Center. It was built and is being operated in collaboration with Penn State, the Los Alamos National Laboratory, and General Dynamics in the U.S.; the University of Leicester and Mullard Space Sciences Laboratory in the United Kingdom; Brera Observatory and the Italian Space Agency in Italy; plus partners in Germany and Japan.