HARVARD GAZETTE ARCHIVES

A flash of high energy radiation from a massive dying star sterilizes an Earth-like planet too close to escape the blast in this artist's rendering. (Artist rendering by David A. Aguilar/CfA)

"This is the first time anyone has seen infrared light simultaneously with a gamma-ray burst," said Cullen Blake, graduate student at the Harvard-Smithsonian Center for Astrophysics and lead author on the paper. "This burst filled in a piece of the puzzle we didn't even know was missing."

The ability of PAIRITEL to quickly and automatically aim at an object of interest proved key to obtaining this result. PAIRITEL pointed in the direction of the burst minutes after the Integral gamma-ray satellite detected it. As a result, astronomers spotted infrared light from the explosion while the gamma-ray burst was ongoing.

"Gamma-ray bursts have been studied for 35 years, and we thought that GRBs were just that - a burst of gamma-ray and X-ray light," said Joshua Bloom (former Junior Fellow at the Society of Fellows and now assistant professor at the University of California, Berkeley), who developed the PAIRITEL telescope. "Our new data offer a more expansive view - that whatever is producing the gamma rays is also capable of producing optical and infrared light."

Time line of a landmark burst

On Dec. 19, 2004, the orbiting Integral satellite detected the GRB and radioed its coordinates in the constellation Cassiopeia to astronomers worldwide. (The burst was also only the third burst to be localized by NASA's new GRB satellite, Swift.) The PAIRITEL telescope slewed to the coordinates as soon as it received the alert and within seven minutes of the start of the burst, PAIRITEL began observations. The GRB occurred somewhere in the field of view of PAIRITEL, but the precise position was not yet known.

"I was in a movie theater when I got a page that a burst had happened," said Blake. "As soon as I got home, I started looking at the images from the telescope and comparing them with older images at that place in the sky. Quickly I realized that we had something exciting!"

The images showed a new point of light in the area of sky of the GRB, one not present in archival images. Blake and Bloom then relayed the discovery to other astronomers, allowing others to train their telescopes on the precise position.

Intriguingly, the infrared light from that new source flickered during the first minute of observing, while the burst was taking place. That correlation implied that both the gamma rays and infrared light were coming from the same region near the exploding star.

Physics of a gamma-ray burst

The picture that has emerged to explain GRBs is that when massive stars expend their nuclear fuel, they catastrophically collapse and form a black hole. Jets formed near the black hole plow outward and accelerate to velocities very near the speed of light. The jets contain relativistic winds that interact and collide, creating shock waves and emitting high-energy X-rays and gamma rays. If certain conditions arise, the shock waves may also generate infrared light.

Hours after the initial burst, PAIRITEL detected the traditional infrared afterglow from the GRB. An afterglow is generated when the jets hit shells of material surrounding the exploded star. Observations of GRB afterglows may offer astronomers a way of studying the environment immediately surrounding the bursts.

More information about PAIRITEL and the Swift satellite can be found at http://pairitel.org and http://swift.gsfc.nasa.gov.

For a related story about the discovery of a new planet through "microlensing," visit http://www.cfa.harvard.edu/press/pr0514.html.