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Mysterious cosmic radio bursts found to repeat

New observations provide strong evidence for multiple populations of Fast Radio Bursts

March 02, 2016

An international research team including astronomers from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, has discovered the first source of repeating bursts of radio waves which is located well beyond our Milky Way galaxy. Fast radio bursts (FRBs), lasting just a few thousandths of a second, have puzzled scientists since they were first reported nearly a decade ago. The findings indicate that these “fast radio bursts” come from an extremely powerful object which occasionally produces multiple bursts in under a minute.

Their results are published in this week’s online edition of Nature.
<p><em>The 305-m Arecibo telescope and its suspended support platform of radio receivers is shown amid a starry night. &nbsp;From space, a sequence of millisecond-duration radio flashes are racing towards the dish, where they will be reflected and detected by the radio receivers. &nbsp;Such radio signals are called fast radio bursts, and Arecibo is the first telescope to see repeat bursts from the same source.</em><strong> &nbsp;</strong></p> Zoom Image

The 305-m Arecibo telescope and its suspended support platform of radio receivers is shown amid a starry night.  From space, a sequence of millisecond-duration radio flashes are racing towards the dish, where they will be reflected and detected by the radio receivers.  Such radio signals are called fast radio bursts, and Arecibo is the first telescope to see repeat bursts from the same source.  

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“We’ve never before seen any FRB repeat, but to be sure we continued to monitor a previously discovered FRB over many months,” says Laura Spitler, lead author of the new paper and a postdoctoral researcher at the MPIfR. The observations were performed with the Arecibo radio telescope in Puerto Rico – the world’s largest radio telescope with a diameter of 305 meters.

Until now most theories about the origin of these mysterious pulses have involved cataclysmic incidents that destroy their source – a star exploding in a supernova, for example, or a neutron star collapsing into a black hole. That changed last November, when McGill University PhD student Paul Scholz was sifting through results from these monitoring observations and found 10 more bursts. “The repeat signals were surprising – and very exciting,” Scholz says. “I knew immediately that the discovery would be extremely important in the study of FRBs.”

This finding suggests that these bursts must have come from an exotic object, such as a rotating neutron star having unprecedented power that enables the emission of extremely bright pulses, the researchers say.  It is also possible that the finding represents the first discovery of a sub-class of the cosmic FRB population.

“Not only does this source repeat, but the brightness and spectra of the bursts also differs from those of other FRBs,” notes Laura Spitler. Additional evidence for multiple classes of FRBs also comes from a study to be published soon in Monthly Notices of the Royal Astronomical Society, which reports on the first FRBs with two peaks, found using the Parkes radio telescope in Australia. “The emission of two pulses separated by only a few thousandths of a second is most easily explained by extreme flaring in a neutron star,” explains Dr. David Champion, an astronomer at the MPIfR and the lead author of this study.

<p><em>The initially discovered &ldquo;Burst 1&rdquo; and 10 new bursts seen from the fast radio burst source FRB 121102. &nbsp;The bursts are shown as a function of radio observing frequency, and the signal summed across all observed frequencies is shown at the top in each case. &nbsp;</em></p> Zoom Image

The initially discovered “Burst 1” and 10 new bursts seen from the fast radio burst source FRB 121102.  The bursts are shown as a function of radio observing frequency, and the signal summed across all observed frequencies is shown at the top in each case.  

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Intriguingly, the most likely implication of the new Arecibo finding – that the repeating FRB originates from a young extragalactic neutron star – is seemingly at odds with the results of a study published last week in Nature by another research team, where Bonn researchers were also involved. That paper suggested FRBs are related to cataclysmic events, such as short gamma-ray bursts, which cannot generate repeat events.  Both findings together strongly imply that there are at least two different kinds of FRB sources.

In the future, the team hopes to learn more about the source through observations at other wavelength regimes. “We are going to compare our radio observations with observations from optical and X-ray telescopes,” says Jason Hessels, associate professor at the University of Amsterdam and the Netherlands Institute for Radio Astronomy as well as corresponding author of the Nature paper.  “It’s an exciting time for FRB studies. You can learn something new with almost every new source”, he concludes.

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Scientists from Max Planck Institute for Radio Astronomy involved in this research were Laura Spitler, the first author, Paulo Freire, Patrick Lazarus and Weiwei Zhu.

The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. Méndez-Universidad Metropolitana, and the Universities Space Research Association.

The research was supported by grants from the European Research Council, the National Science and Engineering Council of Canada, and the American National Science Foundation.

 

 

 
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