Giant New Telescope Bags Gamma Ray Burst

The Very Large Telescope (VLT) in Chile, the world's most powerful telescope, has bagged its first gamma ray burst, less than 6 weeks after the start of its regular observations. Astronomers say studies of the afterglow seem to support a budding theory that these mysterious explosions emit radiation in two opposing beams, making them visible at great distances when one of the beams happens to be directed at Earth.

The burst, now named GRB990510, was first detected by two satellites, NASA's Compton Gamma Ray Observatory and the Italian-Dutch satellite BeppoSAX. Both saw a bright flash of gamma rays on Monday 10 May, around 08.49 Universal Time. Simultaneous x-ray observations by BeppoSAX pinpointed the sky position of the burst near the celestial south pole, and within 10 hours, astronomers had spotted a relatively bright but fading optical counterpart with the 1-meter Sutherland telescope at the South African Astronomical Observatory.

Astronomers Titus Galama and Paul Vreeswijk of the University of Amsterdam, who are coordinating the follow-up observations of the burst, also trained the VLT at the burst. Using the first of the VLT's four 8.2-meter telescopes, they succeeded in obtaining the spectrum of its optical counterpart. From the redshift of the spectral lines, caused by the expansion of the universe, they conclude that the burst took place more than halfway across the universe. Galama says a wealth of observations have been obtained so far. "We're still analyzing the data," he says, "but we'll probably learn a lot from this burst."

Astronomer Shrinivas Kulkarni and his colleagues from the California Institute of Technology (Caltech) are studying GRB990510, too. Kulkarni and his colleagues are using the Australian Telescope Compact Array for radio observations of the burst's afterglow. And in observations obtained by a 1.25-meter telescope at Mount Stromlo Observatory in New South Wales, Kulkarni says he can see hints that most of the energy of the burst was emitted in two opposing beams or jets--a possibility first supported by extensive studies of another burst, earlier this year (ScienceNOW, 25 March 1999).