Astronomers report on brightest gamma-ray burst

Astronomers from the U.S. and Europe said Thursday they had observed the brightest gamma-ray burst (GRB) ever recorded in the relatively nearby universe, a finding that could lead to a rewrite of standard theories on how the blast occurs. The event, named GRB 130472A, was observed by several space- and ground-based telescopes on April 27. The findings were reported in four papers published by the U.S. journal Science. "We suddenly saw a gamma-ray burst that was extremely bright -- a monster gamma-ray burst," astrophysicist Daniele Malesani of the University of Copenhagen, Denmark, said in a statement. "This is one of the most powerful gamma-ray bursts we have ever observed." Several features of GRB 130472A make it of particular interest to astronomers. First, the blast occurred 3.6 billion light-years away from the Earth, which is less than half the distance of the typical GRB. Its record-setting 20-hour duration was longer than any other GRBs observed previously. And, in addition to being the brightest GRB ever witnessed, it was also one of the most energetic. "When that happens, we start seeing features that we were not able to observe before," said Nicola Omodei, a research associate at the Stanford University who led data analysis for one of the Science papers. "Especially because it was very bright, you can uncover features that were not predicted by the standard models." For instance, the telescopes detected more photons and more high-energy gamma rays than theoretical models would predict for a burst of this magnitude, the researchers said. In particular, a few of these high-energy events are so energetic that they cannot be produced via existing models. The researchers said that the new observations don't rule out the existing model, but scientists will need to either amend portions of it or adopt a new theory altogether to account for these characteristics. The researchers also followed the so-called afterglow of the blast, which usually lasts a few days or several weeks, from both the Swift satellite and from the ground-based telescopes. In this case, the burst was so powerful that they could observe the afterglow for several months. By analyzing the light from the afterglow, the researchers studied its spectral composition, which can reveal the properties of the original star. "What we have discovered is that it is a giant star with a mass that is 20-30 times the mass of the Sun, and rapidly rotating. But its size is only 3-4 times that of the Sun, so it is extremely compact," Malesani added.