Los Alamos gamma ray burst work advances on satellite

Contact: Nancy Ambrosiano, nwa@lanl.gov, (505) 665-4610 (00-133)

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LOS ALAMOS, N.M., Oct. 6, 2000 -- They burn as brightly as 100 million billion stars, flash randomly across the heavens, and were discovered more than 25 years ago here at the US Department of Energy’s Los Alamos National Laboratory. Now, with tomorrow’s launch of the High Energy Transient Explorer, gamma ray bursts (GRBs) will begin to reveal more of their secrets as the latest in detection equipment is lifted into orbit.

The HETE-2 satellite, hailed as the next big thing in gamma ray burst research, is carrying cutting-edge equipment and software thanks in part to Laboratory Fellow Edward E. Fenimore and Mark C. Galassi. Scheduled to fly on Saturday from Kwajalein Missile Range, Marshall Islands, aboard a Hybrid Pegasus launch vehicle, the satellite will carry the ability to notify researchers of a gamma ray burst in mere seconds. And since the bursts are powerful but ephemeral, that rapid alert will make all the difference between catching GRB images and information, and simply speculating about what just happened.

For Fenimore, it will be the culmination of 17 years of planning and work on such a satellite, and the second attempt to lift the team’s creation into the sky. The first mission, HETE, was destroyed in 1996 by a rocket malfunction.

It’s a never-ending project, even when it’s successful, Fenimore said. "These instruments often become like a child: you stay up all night with it, you constantly thinking of things that might go wrong and what can be done to mitigate any ill effects. This child can take a decade to leave the house and you still have to care and feed it after it gets on orbit."

Presuming the rocket makes it successfully into space and deploys the satellite at an appropriate location (propelled into a 370-mile by 400-mile elliptical orbit, after being carried by plane to 40,000 feet above the Pacific), Fenimore, Galassi and the Massachusetts Institute of Technology team to which they belong will then wait for the vehicle to work its way into an effective scientific "conversation" with the ground crews.

The technical advances on this project are considerable. Galassi notes that "HETE has 12 networked computers with a sophisticated message-passing architecture that allows the instruments to interact with each other and influence each other's behavior -- probably the most complex software ever flown on a satellite of this size."

The key to the speedy identification and notification of burst and other fleeting cosmic events is that the satellite has to autonomously locate the gamma ray burst by processing the images right there, on board. That's work that is normally done with a lot of hands-on by people on the ground.

"HETE-2 may well revolutionize the field of high-energy astronomy by alerting optical and radio observatories when gamma-ray bursts are in progress, and precisely where observers should look," said Dr. George R. Ricker of MIT, principal investigator of the HETE-2 mission.

HETE-2 is equipped with instruments sensitive to gamma- and X-radiation. These instruments share a common field of view of ~1.5 steradians, span a detectable energy range of about 3 decades, and are capable of immediate inter-instrument communication.

The gamma-ray instrument, FREGATE, is sensitive to photons in the 6-400 keV energy range. It will provide accurate burst triggers and moderate resolution spectra. FREGATE was built by the CESR in Toulouse, France.

The wide-field X-ray Monitor (WXM) is sensitive in the 2-25 keV energy range, with good energy resolution and localization accuracy to ~10 arc-minutes or better. The WXM detectors were built by RIKEN and Los Alamos.

The soft X-ray camera (SXC) is sensitive in the 0.5-10 keV energy range, with very good energy resolution and localization accuracy to 30 arc-seconds or better, according to the MIT staff. The SXC was built by the Center for Space Research at MIT

Each HETE-2 instrument operates independently of the others; however, if a burst is detected by one of the instruments, the others are notified and begin collecting data at higher temporal and energy resolution. All instruments use on-board sensors to determine safe and appropriate operational conditions.

The HETE-2 is a collaboration between NASA; MIT; Los Alamos National Laboratory, New Mexico; France's Centre National d'Etudes Spatiales (CNES), Centre d'Etude Spatiale des Rayonnements (CESR), and Ecole Nationale Superieure de l'Aeronautique et de l'Espace (Sup'Aero); and Japan's Institute of Physical and Chemical Research (RIKEN). The science team includes members from the University of California (Berkley and Santa Cruz) and the University of Chicago.

See more information on this mission at http://space.mit.edu/HETE/.

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