Washington, Jan 9: Astronomers have detected the traces of a cosmic explosion known as a short gamma-ray burst (GRB) from further back in time than ever before, specifically 7.4 billion years ago.

"This discovery dramatically moves back the time at which we know short GRBs were exploding. The short burst is almost twice as far as the previous confirmed record holder," said John Graham of the Johns Hopkins University, in Baltimore, Md.

GRBs are among the most powerful explosions in the universe, releasing enormous amounts of energy in the form of X-rays and gamma rays. Most bursts fall in one of two categories: long bursts and short bursts, depending on whether they last longer or shorter than three seconds.

Detected by NASA’s Swift satellite in the constellation Taurus, the latest burst is known as GRB 070714B, whose high energy and 3-second duration firmly places it in the short GRB category.

Rapid follow-up observations with the 2-meter Liverpool Telescope and the 4-meter William Herschel Telescope found an optical afterglow in the same location as the burst, which allowed astronomers to identify the GRB’s host galaxy.

Using the 8-meter Gemini North Telescope in Hawaii, Graham and his colleagues, Andrew Fruchter of the Space Telescope Science Institute, in Baltimore, and Andrew Levan of the University of Warwick, UK, revealed that the host galaxy has a spectral line from ionized oxygen.

Now, the amount that line was shifted toward the red end of the spectrum yields a redshift of 0.92, which translates to a distance of 7.4 billion light-years. This means the explosion occurred 7.4 billion years ago.

"The fact that this short burst is so far away means this subclass has a broad range of distances, although they still tend to be closer on average than long GRBs," said Swift scientist Neil Gehrels of NASA’s Goddard Space Flight Center in Greenbelt, Md.

"We now have a good idea of the type of star that produces the brighter long bursts. But how short bursts are formed remains a mystery," saidFruchter. (ANI)