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Mystery outburst from across the Universe is caught in a flash

Paul Sutherland, Feature writer
Jan 19, 2015, 18:08 UTC

Sen—A brief and mysterious type of radio signal that has been puzzling astronomers for seven years has been caught live for the first time.

The short, sharp flash, dubbed a fast radio burst (FRB), was observed by the Parkes radio telescope in Australia, famous for its starring role in comedy movie The Dish.

This telescope, operated by Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) in New South Wales, has been the prime discoverer of these outbursts, having detected the first five, with one other observed by the Arecibo telescope in Puerto Rico. 

But they were all found in previously recorded data that was being re-examined, and astronomers admit they really have no clear idea yet what causes them.

The first, discovered by chance in 2007 as scientists were checking for something else, lasted just a few milliseconds. As more were found, the only thing that astronomers seemed sure of was that they were from outside our Galaxy.

Dr Megan Argo, a radio astronomer working with the e-Merlin array, based at Jodrell Bank in the UK, told Sen: “The first fast radio burst, known as the Lorimer burst, was discovered by accident years after it was detected, when old archive data was being analysed in a new way. 

“Since then, much more archive data has been searched, and a handful more found. At first, they were all were detected in data from Parkes, so there was some scepticism. Were they being produced by local interference perhaps, or some other oddity specific to Parkes?

“But then another FRB was discovered in archived date from another radio telescope, the giant Arecibo dish in Puerto Rico.”

The latest discovery, reported in the Monthly Notices of the Royal Astronomical Society, was made by PhD candidate Emily Petroff. She said in a statement: “These bursts were generally discovered weeks or months or even more than a decade after they happened! We’re the first to catch one in real time.”

In her quest to catch such an event, Petroff, from the Swinburne University of Technology in Melbourne, had a number of international observatories on standby to make follow-up observations at several wavelengths in the spectrum, from radio to X-rays.

Teams swung into action on 12 telescopes around the globe in Australia, California, the Canary Islands, Chile, Germany, Hawaii, and India, and also in space. But they saw nothing in optical, infrared, ultraviolet or X-ray light.

That appears to rule out certain causes of the flashes, such as long gamma-ray bursts or nearby supernovae. 

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An artist's impression of a magnetar, which is one possible cause being considered for a fast radio burst. Image credit: ESO/L. Calçada

Dr Argo told Sen: “Known types of transient (non-repeating) events, such as supernovae and gamma-ray bursts, are usually detected in more than one part of the spectrum, and usually produce afterglows which can remain detectable over days or months. But in this case of FRBs, no other signals have been detected from the same location on the sky.

“This means we still have limited knowledge as to the nature—and exact location—of the host galaxy and the object producing the burst, but can rule out events of most known types in the local Universe.”

Though astronomers are unsure what objects are causing the flashes, there were characteristics of the signal that give them reason to believe it came from a distance of 5.5 billion light-years, showing it must have been incredibly powerful.

One thing the live outburst did tell the astronomers was the direction in which the radio waves were oriented, known as polarisation. This showed that there might be magnetic fields near the source of the FRB.

Dr Argo told Sen: “The peculiar thing with this burst is its polarisation characteristics. Only certain physical processes cause light to be polarised, and none of them perfectly matches the characteristics of this signal.  

“What we do know is that the event appears to be outside the Milky Way, very energetic, very short, from a very small physical region, and different to previously known astrophysical transient objects.”

It has been suggested that low-energy gamma-raybursts and flares from the most magnetic, dense stars in the Universe, called magnetars, are possible candidates for the flashes, as well as imploding neutron stars or black holes.

Dr Argo pointed out that powerful new tools will help astronomers better pinpoint such phenomena. She told us: “New telescopes like LOFAR (the Low-Frequency Array for radio astronomy) in Europe and the MWA (Murchison Widefield Array) in Australia were designed to be capable of looking for these short events over much larger areas of the sky. 

“And one of the science goals for the Square Kilometre Array (SKA) in southern Africa and Australia is to better localise transient events, and look for evidence of highly energetic events (predicted but not yet observed) such as the merger of neutron stars or evaporating black holes.”

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