Hunting Gamma-ray Bursts

The Swift Satellite

Data from the Swift satellite's ultraviolet/optical and x-ray telescopes show one of the most distant gamma-ray bursts ever detected. It's so distant that the star that died to create it exploded when the universe was about 630 million years old. Credit: NASA/Swift/Stefan Immler

In the June edition of The Astronomer’s Universe, I talk about gamma-ray bursts with Dr. Dale Frail of the Very Large Array (VLA) in New Mexico.  Gamma-ray bursts (commonly referred to as GRBs) are strong blasts of gamma rays that astronomers have detected from nearly every direction in the universe. The first ones were detected by a military satellite back in the early days of the space age, and nobody knew quite what to make of them.  Today, we have satellites in constant watch for GRBs (as they are called), including NASA’s Swift mission.

Swift is an international mission with scientists from U.S., Italy, and the United Kingdom participating.  It has three main instrument packages that let it study GRBs in great detail. In the six years since its launch, Swift has seen more than 500 GRBs and it continues to monitor the skies constantly for more of these outbursts.

What instruments does Swift use to watch for these titanic outbursts that appear so briefly in our skies?  The first is the so-called Burst Alert Telescope (BAT). It looks f0r bursts in the energy range of 15 to 150 keV (shorthand for kilo-electron volt, a measure of energy). The BAT calculates the position of the burst that it sees and if the burst is strong enough, the whole spacecraft slews around to take a closer look.

Swift also has an x-ray telescope and UV/optical telescope, both of which study the afterglows of the gamma-ray burst in their respective wavelength ranges.  A GRB is going to have a certain amount of its radiation in the optical, ultraviolet, and x-ray ranges, as well. Studying all four (gamma, x-ray, optical, and ultraviolet) gives the most complete “picture” of the GRB.

The positions of GRBs that Swift finds are relayed to ground-based observatories so that astronomers can continue to study the afterglows of GRBs long after the inital burst has faded away. The data that astronomers get from Swift and all the other instruments used to monitor the GRBs (such as the radio telescopes of the VLA), are going a long way toward giving astronomers a much fuller picture of just what causes these monster explosions in distant space.