Swift Team Finds Bright Burst

Astronomers have found by far the most distant object ever seen by the naked eye -- a gamma ray burst from 7.5 billion light-travel years away.

"The object that exploded produced more optical light than anything else we have ever seen," said Paul O'Brien, a senior lecturer of physics and astronomy at Leicester University in Leicester, England, in an e-mail. "It was, at peak, approximately equivalent to a few hundred million billion suns!"

O'Brien is one of a large team of scientists around the world who continually monitor gamma-ray bursts, or GRBs, found by the Swift satellite. Swift is part of NASA's medium-explorer program, the first multiwavelength observatory dedicated to the study of gamma-ray burst science.

GRB080319B (Photo: NASA/Swift/Stefan Immler)

Gamma-ray bursts are the most powerful explosive events in the universe. They occur in far-off galaxies, so they are usually faint. But on the morning of March 19, the Swift satellite found a burst so bright it could have been seen without binoculars or a telescope -- even though it was 7000 times further away than the Andromeda galaxy.

The new GRB -- known unceremoniously as GRB-080319B -- was discovered "on a fantastic day for GRB hunters," the university said in a statement. Swift typically finds only two a week, but for the first time it found five bursts within 24 hours. The second burst of the day is the new record holder. The enormous energy released in the explosion -- brighter than the light from all of the stars in five million Milky Way Galaxies -- was caused by the death of a massive star, which collapsed to form a black hole.

Julian Osborne of the University of Leicester, lead investigator for the Leicester University-based Swift UK Science Data Centre, said, “It’s great to find so many GRBs in one day, and the discovery of the brightest burst ever seen will allow us to explore this incredible explosion in exquisite detail.”

The 2m Faulkes Telesope North (Maui, Hawaii), one of the telescopes used to observe the gamma-ray burst. Left to right: Researchers Paul O'Brien, Chris Mottram, Nigel Bannister and Iain Steele. O'Brien and Bannister are with Leicester University, Mottram and Steele with Liverpool John Moores University. All have been involved in follow-up observations of the GRB. (Photo: Paul O'Brien)

The university's Gemini observations allowed scientists to measure the distance to the GRB and to investigate the behavior of gas close to the burst as it was blasted by the energy of the explosion. The Gemini Observatory is an international collaboration that has built two identical eight-meter telescopes, at Mauna Kea, Hawaii (Gemini North) and Cerro Pachón in central Chile (Gemini South), providing full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.

The Swift carries three telescopes: the Burst Alert Telescope (BAT) -- known as Swift's GRB watchdog -- which finds GRBs using gamma-rays in the 15-350 keV band; the X-ray Telescope (XRT), which observes in the 0.3-10-kev x-ray band; and the Ultraviolet and Optical Telescope (UVOT), which observes in the ultraviolet and optical range using a number of filters.

The location of the burst was rapidly pinpointed using the UK-built x-ray and optical cameras. The XRT is a Wolter 1 telescope, which focuses x-rays onto a camera equipped with an EEV CCD 600-by-600 pixel detector. This detects x-ray photons providing position and spectral information simulataneously. The UVOT is a 30-cm aperture Ritchey-Chretien reflector equipped with a micro-channel plate intensified CCd (MIC) detector. This is a very low-noise photon counting device. The UVOT provides the most accurate location, O'Brien said.

He said a number of on-duty scientists at Leicester respond within minutes when alerted to a GRB, which occur at random. "This is required to ensure spacecraft safety and to ensure we trigger observations on other telescopes if the GRB is particularly interesting, as in this case."

Astronomers around the world are now observing the glow from GRB080319B as it fades away. These include UK teams from the Universities of Leicester, Warwick and Hertfordshire, using the Gemini-North Telescope, and the Liverpool John Moores University, using the Liverpool Telescope on La Palma in the Canary Islands, owned and operated by that univeristy's Astrophysics Research Institute.

Spotters are alerted to potential GRBs by mobile phone and e-mail, then complete various tasks, including looking at the Swift data or activating other telescopes. When a burst is detected, the team confers in a conference call.

"Swift will observe the GRB automatically, following a preprogrammed sequence, for a day or two even if we do nothing, "O'Brien said. "Every weekday, we hold a planning meeting (around lunchtime in the UK) at which subsequent observations are discussed and further observations can be requested -- which happened for this one, so we are continuing to observe it. As new GRBs are found, we decide whether to stop observing older ones. GRB080319B has priority at the moment."

O'Brien said working on this project is "certainly the most exciting and demanding work I've ever been involved with. You have to think fast and make sense of a rapidly changing object that will quickly fade away, never to return. You cannot put the object to one side and return to it later."

He added, "This is exactly the kind of science that can alter our view of the universe, as we literally don't know what is going to happen next. The bright burst found on March 19 is an amazing object and a reminder that we should continue to look at the sky, as our ancestors did."

For more information, visit: www.swift.ac.uk