Home galaxy found for fast radio burst

Artist’s concept by Bill Saxton via NRAO/ AUI/ NSF; Hubble Legacy Archive, ESA, NASA

Astronomers meeting this week in Grapevine, Texas for the 229th meeting of the American Astronomical Society are abuzz with the news that a sporadically repeating, milliseconds-long fast radio burst has now been identified with a precise location in the sky. They see a dwarf galaxy at this sky location and believe the burst is emanating from this little galaxy, which is some 3 billion light-years away. Their work is published January 4, 2017 in the peer-reviewed journal Nature. Astronomer Shami Chatterjee of Cornell University is the first author.

It’s exciting, because it’s the first time they’ve been able to identify a fast radio burst’s home galaxy. And it’s surprising, because the galaxy is a dwarf and not a bigger, more glamorous galaxy. Astronomers say the new information rules out several suggested explanations for the cause of fast radio bursts, which were first discovered in 2007, in archived data taken in 2001 by the Parkes radio telescope in Australia.

Sarah Burke-Spolaor, an astronomer at the National Radio Astronomy Observatory in Socorro, New Mexico, and West Virginia University in Morgantown was quoted in Nature as saying:

This detection has really broken open the gates of a new realm of science and discovery.

View larger. | Visible-light image of the host galaxy of the fast radio burst FRB 121102. Image via NRAO/ Gemini Observatory/AURA/NSF/NRC.

There are only 18 known fast radio bursts, and they are very mysterious. Known to astronomers as FRBs, these bursts pack an energetic punch, but are short-lived, only milliseconds in length. The National Radio Astronomy Observatory explained in a statement:

All were discovered using single-dish radio telescopes that are unable to narrow down the object’s location with enough precision to allow other observatories to identify its host environment or to find it at other wavelengths. Unlike all the others, however, one [fast radio burst], discovered in November of 2012 at the Arecibo Observatory in Puerto Rico, has recurred numerous times.

The repeating bursts from this object, named FRB 121102 after the date of the initial burst, allowed astronomers to watch for it using the National Science Foundation’s (NSF) Karl G. Jansky Very Large Array (VLA), a multi-antenna radio telescope system with the resolving power, or ability to see fine detail, needed to precisely determine the object’s location in the sky.

In 83 hours of observing time over six months in 2016, the VLA detected nine bursts from FRB 121102.

That string of nine bursts was unprecedented in this sort of study. It let astronomers narrow down the position of FRB 121102 very precisely. They then used the Gemini North telescope in Hawaii to make a visible-light image that identified a faint dwarf galaxy at the location of the bursts and to determine that the dwarf galaxy is more than 3 billion light-years from Earth.

In addition to detecting the bright bursts from FRB 121102, the VLA observations also revealed an ongoing, persistent source of weaker radio emission in the same region.

National Radio Astronomy Observatory VLA fast radio burst animation from NRAO Outreach on Vimeo.

More observations – this time using the multiple radio telescopes of the European VLBI Network, along with the 1,000-foot-diameter William E. Gordon Telescope of the Arecibo Observatory, and the NSF’s Very Long Baseline Array (VLBA) – let the astronomers determine the object’s position with even greater accuracy. Jason Hessels of the Netherlands Institute for Radio Astronomy and the University of Amsterdam – a member of the discovery team – said:

These ultra high precision observations showed that the bursts and the persistent source must be within 100 light-years of each other.

The astronomers now believe the bursts and continuous source are likely to be either the same object or that they are somehow physically associated with each other. The top candidates, the astronomers suggested, are a neutron star, possibly a highly-magnetic magnetar, surrounded by either material ejected by a supernova explosion or material ejected by a resulting pulsar, or an active nucleus in the galaxy, with radio emission coming from jets of material emitted from the region surrounding a supermassive black hole.

But astronomers are still cautious in drawing conclusions because FRB 121102 is the only one known to repeat. So it might be physically different from the others.

Further studies are planned.

The Very Large Array – on the Plains of San Agustin, some 50 miles west of Socorro, New Mexico – was instrumental in finding a host galaxy for the fast radio burst FRB 121102.

Bottom line: Astronomers were able to pinpoint the location in the sky of a fast radio burst known as FRB 121102 and, in that way, determine its home galaxy. The galaxy is a little dwarf galaxy, 3 billion light-years away.


January 5, 2017

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