Unusually long-lasting gamma ray bursts observed

WASHINGTON, April 16 (Xinhua) -- Astronomers said Tuesday that they have pinpointed a new type of exceptionally powerful and long-lasting blasts of high energy gamma rays, known as gamma ray bursts (GRB).

While most bursts are over in about a minute, this new type can last for several hours, according to a new study presented at the GRB 2013 Symposium in Nashville, Tennessee.

Three of these unusual long-lasting blasts have recently been discovered using the Swift satellite and other international telescopes, and one, GRB 101225A, exploded on Christmas Day in 2010, is the first GRB ever observed, with a duration of at least two hours.

"We have seen thousands of gamma-ray bursts over the past four decades, but only now are we seeing a clear picture of just how extreme these extraordinary events can be," said Bruce Gendre, a researcher associated with the French National Center for Scientific Research in a statement.

Using data from the Gemini Telescope in Hawaii, the researchers calculated that the first GRB, nicknamed the "Christmas burst", occurred at a location of approximately halfway to the edge of the observable universe, or 7 billion light-years away.

Armed with its location, they had developed a new theory to explain how it occurred. They suggest this kind of burst is caused by a supergiant, a star 20 times more massive than the Sun, which evolves to become among the biggest and brightest stars in the universe with a radius of up to 1 billion miles -- up to 1,000 times that of the Sun.

They believe the ultralong durations of the Christmas GRB and two other similar bursts are simply due to the sheer size of the supergiants exploding in a supernova.

Most stars that create gamma-ray bursts are thought to be relatively small and dense, and the explosion that destroys them punches through the star in a matter of seconds. In the case of these new ultralong bursts the explosion takes much longer to propagate through the star, and so the gamma-ray burst lasts for a much longer time, according to the study.

"These events are amongst the biggest explosions in nature, yet we're only just beginning to find them," said Andrew Levan, an astronomer at the University of Warwick in England and one of the authors of the study. "It really shows us that the universe is a much more violent and varied place than we'd imagined."