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Astronomers pinpoint radio flashes from long-long ago in a galaxy far-far away

Published on 22 December 2016


Astronomers - among them scientists from ASTRON, University of Amsterdam, Leiden University and JIVE in the Netherlands - have for the first time pinpointed the location of a so-called ‘fast radio burst' - a type of short-duration radio flash of enigmatic origin - and have used this to identify its host galaxy. The team presented their findings at the American Astronomical Society's winter meeting in Grapevine, Texas. The results appear today in Nature and the Astrophysical Journal Letters.

Prior to this discovery, astronomers have lacked the definitive proof that fast radio bursts (FRBs) come from far outside our Milky Way galaxy, because poor localization has prevented them from uniquely identifying their galaxy of origin. The new finding is critical because it has also allowed astronomers to precisely measure the distance to the extragalactic source, and hence how much energy it is producing.

FRBs are visible for only a fraction of a second, and have puzzled astronomers for over a decade since they were first discovered. Precise localization of an FRB requires radio telescopes separated by large distances, which allow high resolution images to be made when these telescopes are used in combination with each other.

On Aug 23 2016, the Karl G. Jansky Very Large Array in New Mexico first detected a radio burst from the only known repeating FRB, named FRB 121102. This determined its sky position to a fraction of an arcsecond. "Near this position, our team found both steady radio and optical sources, which arguably pointed the way to the galaxy hosting the FRB," says first author Shami Chatterjee (Cornell).

The team wanted to zoom-in even further, so they used the Arecibo Observatory and the European VLBI Network (EVN), which links telescopes spread across the world, to localize the position by another factor of 10 more precision. "With this level of precision, we have strong evidence that the source of the bursts is physically related to whatever is producing the persistent radio emission," says Benito Marcote (JIVE). "It is the combined sensitivity of EVN telescopes, their large separation and the unique capabilities of the EVN central data processor at JIVE that allow for pinpointing events that are as short as a thousandth of a second, with a sky position accuracy of about 10 milli-arcseconds, which is similar to the apparent size of a tennis ball in New York, seen from the Netherlands," adds Zsolt Paragi (JIVE).

The team used one of the world's largest optical telescopes, the 8-m Gemini North on Mauna Kea in Hawaii, to discover that the bursts originate from a host galaxy, and use its measured spectrum to obtain a so-called ‘redshift', which places the source at a whopping distance of over 3 billion light-years. "This gives us incontrovertible confirmation that this FRB originates very deep in extragalactic space," says co-author Cees Bassa (ASTRON). Though the mystery of the FRB's distance is now solved, astronomers have a new puzzle on their hands. The galaxy hosting the FRB is surprisingly small - a so-called dwarf galaxy. "We were not sure what to expect, but I think the whole team was surprised to see that our exotic source is hosted by a very puny and faint galaxy," Bassa adds.

The fact that FRB 121102 is located in a dwarf galaxy may be a vital clue to its physical nature. Such galaxies contain gas that is relatively pristine compared to that found in the Milky Way. "The conditions in this dwarf galaxy are such that it may be possible to form much more massive stars than in the Milky Way, and perhaps the source of the FRB bursts is from the collapsed remnant of such a star,", suggests co-author Jason Hessels (ASTRON, University of Amsterdam). Alternatively, astronomers are considering a very different hypothesis in which the FRBs are generated in the vicinity of a massive black hole that is swallowing surrounding gas.

To try and differentiate between these two scenarios, astronomers are using the world's premier radio, optical, X-ray and gamma-ray telescopes. Hessels: "For example, if we can use the Arecibo telescope to find a periodicity in the arrival times of the bursts, then we will have strong evidence that it originates from a rotating neutron star."

Deciphering the origin of the FRBs will also depend on localizing more such sources, and astronomers are debating whether all FRBs detected to date are of a similar physical origin or whether there are multiple types.

NOVA press release:
http://www.astronomie.nl/#!/index/_detail/gli/astronomers-pinpoint-radio-flashes-long-long-ago-g/99871369487963948962

Video:
https://youtu.be/1t-pKcD0Bsw


Link to papers:
S. Chatterjee, et al. 2017, Nature
http://dx.doi.org/10.1038/nature20797

Tendulkar, S. P., et al. 2017, ApJL, 834, L7
(http://iopscience.iop.org/article/10.3847/2041-8213/834/2/L7)

Marcote, B., et al. 2017, ApJL, 834, L8
(http://iopscience.iop.org/article/10.3847/2041-8213/834/2/L8)

More information:

Contacts:

Prof. dr. Huib Jan van Langevelde, JIVE, the Netherlands
E-mail: langevelde@jive.eu
Phone: +31-521-596515
            +31-6-21201419 

Dr. Zsolt Paragi, JIVE, the Netherlands
E-mail: zparagi@jive.eu
Phone: +31-521-596536

Dr. Benito Marcote, JIVE, the Netherlands
E-mail: marcote@jive.eu
Phone: +31-521-596508

More about VLBI, the European VLBI Network and JIVE

VLBI is an astronomical method by which multiple radio telescopes distributed across great distances observe the same region of sky simultaneously. Data from each telescope is sent to a central "correlator" to produce images with higher resolution than the most powerful optical telescopes.

The European VLBI Network (EVN; www.evlbi.org) is an interferometric array of radio telescopes spread throughout Europe, Asia, South Africa and the Americas that conducts unique, high-resolution, radio astronomical observations of cosmic radio sources. Established in 1980, the EVN has grown into the most sensitive VLBI array in the world, including over 20 individual telescopes, among them some of the world's largest and most sensitive radio telescopes. The EVN is administered by the European Consortium for VLBI, which includes a total of 15 institutes, including the Joint Institute for VLBI ERIC (JIVE).

The Joint Institute for VLBI ERIC (JIVE; www.jive.eu) has as its primary mission to operate and develop the EVN data processor, a powerful supercomputer that combines the signals from radio telescopes located across the planet. Founded in 1993, JIVE is since 2015 a European Research Infrastructure Consortium (ERIC) with six member countries: France, Latvia, the Netherlands, United Kingdom, Spain and Sweden; additional support is received from partner institutes in China, Germany, Italy and South Africa. 

Caption: The globally distributed dishes of the European VLBI Network are linked with each other and the 305-m William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico. Together they have localized FRB121102's exact position within it's host galaxy. Credit: Danielle Futselaar (www.artsource.nl)