Science News Vol 158

October 14 2000

Page 245

COSMIC AFTERGLOW STEALS THE LIMELIGHT

A chance cosmic alignment may have led astronomers to a clearer picture of gamma ray bursts, flashes of high energy radiation that rank as the most powerful explosions known in the universe.

Gamma ray bursts erupt at random and spacecraft detect them about once a day. Theorists have proposed that the burst power a sperical shock wave that slams into surrounding space at nearly the speed of light. The collision generates an afterglow that telescopes can record for days to weeks-first in X rays, then visible light and finally radio waves. But these aftergflows have been too small for a telescope to discern their spatial structures.

Now. researchers suggest they have resolved such a structure for the first time-even though its parent gamma ray burst erupted halfway across the universe. Thanks to some gravitational sleight of hand, researchers last March were treated to a magnified view of a gamma ray burst dubbed GRB 00301C. They report their findings in an upcoming Astrophysical Journal Letter.

According to general relativity a massive object that lies between a more distant body and Earth can act as a gravitational lens, bending and magnifying light from the distant body. The visible light afterglow from GRB 00301C appears to have passed through such a lens. Instead of rapidly fading the light remained bright. It peaked almost 4 days after space craft detected the parent burst.

Radio and visible light wavelengths were amplified by about the same amount-another hallmark of a gravitation lens, note coauthors Peter M Garnavich of the University of Notre Dame in Indiana and Abraham Loeb and Kris Z Stanek of the Harvard Smithsonian Center for Astrophysics in Cambridge Mass.

The duration and amount of brightening match the pattern expected when a lens amplifies the light from a fast moving shock wave. Loeb and Rosalba Perpa then at Harvard Smithsonian , predicted 2 years ago that the afterglow would appear as a thin rapidly expanding ring. As the ring grows larger and seeeps behind the lens, magnification would reach a maximum.

Garnavich's team calculates that the lens weighs about half as much as the sun and may lie in a galaxy about halfway between the burst and Earth.

Abdrew S Fruchter of the Space Telescope Science Institute in Baltimore says, the idea of the lens is fascinating and they might be right. Proof will have to await studies of many more bursts he says.

Loeb estimates that less then 1 percent of all afterglows are magnified by a lens. As more examples are found researcherw will be better able to gauge both the wallop packed by the burst and the nature of the medium encountered by the shock wave, he says. On Oct 9 NASA launched the high energy transient explorer which promises to record many more bursts and repidly alert ground based telescopes to look for aferglows.  R Cowen.

TO RETURN TO THE ALIENS HAVE ARRIVED PAGE     CLICK HERE

TO RETURN TO THE HIDDEN MEANINGS HOME PAGE   BACK TO HOME PAGE