Super-bright gamma ray burst

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Super-bright gamma ray burst visible to naked eye
BY EMILY BALDWIN
ASTRONOMY NOW
Posted: March 25, 2008

An intense stellar explosion - a gamma ray burst (GRB) - detected by NASA’s Swift space telescope, is the most distant object visible to the naked eye and the brightest object ever observed by humans.

GRBs are the most powerful explosive events in the Universe, caused by the death of massive stars which collapse to form a black hole. Swift is dedicated to finding GRBs, and normally detects around two a week, but last week it detected five in the space of 24 hours. The brightest GRB occurred on 19 March in the constellation Bootes, and was so brilliant it could be seen without the aid of a telescope or even binoculars, even though it was seven thousand times further away than the Andromeda galaxy.

The location of the burst was rapidly pinpointed using the UK-built X-ray and optical cameras on Swift. Dr Paul O’Brien of the University of Leicester and a member of the Swift Science Team says, “The explosion happened at a distance of 7.5 billion light years from Earth, half way across the Universe. To detect a naked eye object from such a distance really is extraordinary.”

The gamma ray burst captured in X-ray (left) and optical (right). The apparent extended nature of the X-ray image is due to the X-ray telescope optics. Images courtesy of Dr. O'Brien, University of Leicester.

Astronomers around the world are now observing the decaying glow from this burst as it fades away. These include UK teams from the Universities of Leicester, Warwick and Hertfordshire using the Gemini-North Telescope in Hawaii, and the Liverpool John Moores University using the Liverpool Telescope on La Palma in the Canary Islands. Professor Nial Tanvir, of the University of Leicester, says: “Our Gemini observations allowed us to measure the distance to the GRB, and to investigate the behaviour of gas close to the burst as it was blasted by the energy of the explosion”.

“The speed at which material was coming out from the explosion was moving very, very close to the speed of light,” added O’Brien. The team are still working on the data to learn about the super-bright explosion, including how dense the gas is and how the gas density varies with distance from the burst, as well as why this particular explosion was exceptionally intense. “Perhaps this GRB had an unusually narrow jet - so the energy was concentrated in our direction - or the star that collapsed was unusually massive, spinning very fast or had a very strong magnetic field,” speculates O’Brien. “Bright examples allow us to study more details so we hope this one will help us find some answers.”