* Astronomy

Gamma-Ray Burst Challenges Theory
In a series of landmark observations gathered over a period of four months, NASA's Swift satellite has challenged some of astronomers' fundamental ideas about gamma-ray bursts (GRBs), which are among the most extreme events in our universe. GRBs are the explosive deaths of very massive stars, some of which eject jets that can release in a matter of seconds the same amount of energy that the sun will radiate over its 10-billion-year lifetime.
When GRB jets slam into nearby interstellar gas, the resulting collision generates an intense afterglow that can radiate brightly in X-rays and other wavelengths for several weeks. Swift, however, has monitored a GRB whose afterglow remained visible for more than 125 days in the satellite's X-ray Telescope (XRT).
Swift's Burst Alert Telescope (BAT) detected the GRB in the constellation Pictor on July 29, 2006. The XRT picked up GRB 060729 (named for its date of detection) 124 seconds after BAT's detection. Normally, the XRT monitors an afterglow for a week or two until it fades to near invisibility. But for the July 29 burst, the afterglow started off so bright and faded so slowly that the XRT could regularly monitor it for months, and the instrument was still able to detect it in late November. The burst's distance from Earth (it was much closer than many GRBs) was also a factor in XRT's ability to monitor the afterglow for such an extended period.

Read more

Several times a week, astronomers detect the violent death cry of a massive star -- an extraordinarily energetic release of gamma rays that takes place in just a matter of seconds to minutes, called a gamma-ray burst (GRB). The GRB's ejecta, which is thought to be beamed in narrow jets, slams into interstellar gas at near light speed. This violent collision shocks the material and produces a bright afterglow that can radiate brightly at X-ray and other wavelengths for several days or even a few weeks. But a GRB observed by NASA's Swift satellite on July 29 generated an X-ray afterglow that remained detectable to the spacecraft's X-ray Telescope (XRT) for an astonishing 125 days.

Read more