NASA Detects One Of Closest And Brightest Gamma Ray Bursts

The Universe clearly works weekends; delivering one of the brightest and closest gamma ray bursts yet on Saturday, March 29, at 6:37 a.m. EST.

NASA's High-Energy Transient Explorer (HETE) detected the burst, signaling the birth of a black hole, in the constellation Leo. For more than 30 seconds, the burst out shone the entire Universe in gamma rays, and its afterglow was still over a trillion times brighter than the Sun two hours later. This was the brightest burst yet detected by HETE and is in the top one percent of all bursts in terms of intrinsic brightness. Within seconds, HETE nailed down a location and subsequently relayed the coordinates to the astronomy community, allowing hundreds of scientists and amateur astronomers to join the observation, from Australia to Finland and across the ocean to America. Observations poured in as scientists attempted to unravel what caused the burst. The burst was later identified with a new supernova in a distant galaxy.

Artist concept of the HETE spacecraft.

"This was our biggest one ever, and it didn't get away," said Dr. George Ricker of the Massachusetts Institute of Technology (MIT), Cambridge, Mass., and principal investigator for the HETE mission. "With scores of observations now completed and more on the way, we should get a rather clear picture of what triggered this burst."

Gamma ray bursts are the most powerful explosions in the Universe; likely caused by the death of a massive star, in which the core implodes to form a black hole. Bursts appear to occur randomly, and few last more than a minute, making them hard to study.

HETE detects the fleeting gamma ray and X-ray portions of these bursts, and its prompt localization enables scientists to study the burst afterglow, which can linger from days to weeks in optical light and radio waves. Most bursts originate in the early universe, traveling upwards of 10 billion years at light speed to reach us.

The burst on March 29 was named GRB 030329. Both the burst and its afterglow were brilliant. The burst poured out a thousand trillion, trillion times the gamma rays seen in a solar flare. When measured more than one hour after the burst, the afterglow was still about as bright as a 12th magnitude star. This means it was only about 10 to 100 times dimmer than what can be seen with the naked eye, visible with backyard telescopes. At its peak, the afterglow may have been visible to the naked eye.

The burst originated approximately two billion light years from Earth, which is relatively close. The GRB 030329 redshift measurement was 0.168, making this the second closest burst with a known redshift measurement. (Redshift is a measurement of how light from distant regions of the Universe is "shifted" to lower energy as the Universe expands; the greater the redshift, the greater the distance from Earth.) "Few amateur astronomers are treated to an event that originated billions of light years away," said Ricker.

Bruce Peterson and Paul Price of the Research School of Astronomy and Astrophysics at the Australian National University, Canberra, first identified the burst afterglow. An automated telescope at Japan's RIKEN science institute quickly confirmed the location. Finnish amateur astronomers provided even tighter constraints on the properties of the afterglow. Multiple observations enable a thorough study of the burst environment.

The GRB Coordinates Network (GCN) is a system that distributes locations of GRBs detected by spacecraft and distributes follow-up observation reports submitted by the GRB community.

Gamma ray burst hunters are aided by three new developments: fast triggers from orbiting detectors; fast relays to observers worldwide via the Gamma ray burst Coordinates Network (GCN); and fast responses from ground-based robotic telescopes. HETE is the first satellite to provide and distribute accurate burst locations within seconds.

The GCN, developed and maintained at NASA's Goddard Space Flight Center in Greenbelt, Md., serves as a gamma ray burst hub. HETE signals the GCN, which sends out "phone calls" and email messages to scientists and amateurs worldwide. The GCN Web site also posts scientific information from the astronomers making observations.

HETE was built by MIT as a mission of opportunity under the NASA Explorer Program, with collaboration among U.S. universities, Los Alamos, N.M. National Laboratory, scientists and organizations in Brazil, France, India, Italy and Japan.