Saturday, September 2, 2017

Breakthrough Listen Detects Repeating Fast Radio Bursts from the Distant Universe

Green Bank Telescope. Credit: greenbankobservatory.org

Breakthrough Listen – the initiative to find signs of intelligent life in the universe – has detected 15 fast radio bursts emanating from the mysterious "repeater" FRB 121102. Fast radio bursts, or FRBs, are brief, bright pulses of radio emission from distant galaxies. First detected with the Parkes Telescope in Australia, FRBs have now been seen by several radio telescopes around the world.

FRB 121102 was discovered in 2012, on November 2nd (hence its name). In 2015, it was the first FRB seen to repeat, ruling out theories of the bursts' origins that involved the catastrophic destruction of the progenitor (at least in this particular instance). And in 2016, the repeater was the first FRB to have its location pinpointed with sufficient precision to allow its host galaxy to be identified. It resides in a dwarf galaxy about 3 billion light years away from Earth.

Attempts to understand the mechanism that generates FRBs have made this galaxy a target of ongoing monitoring campaigns by instruments across the globe. Possible explanations for FRBs range from outbursts from rotating neutron stars with extremely strong magnetic fields, to more speculative ideas that they are directed energy sources used by extraterrestrial civilizations to power spacecraft.

Breakthrough Listen is a global astronomical initiative launched in 2015 by Internet investor and philanthropist Yuri Milner and cosmologist Stephen Hawking. As part of their program to observe nearby stars and galaxies for signatures of extraterrestrial technology, the Listen science team at UC Berkeley added FRB 121102 to their list of targets.

In the early hours of Saturday, August 26, UC Berkeley Postdoctoral Researcher Dr. Vishal Gajjar observed the location of FRB 121102 using the Breakthrough Listen backend instrument at the Green Bank Telescope in West Virginia. The instrument accumulated 400 TB of data on the object over a five hour observation, observing the entire 4 to 8 GHz frequency band. This large dataset was searched for signatures of short pulses from the source over a broad range of frequencies, with a characteristic dispersion, or delay as a function of frequency, caused by the presence of gas in space between us and the source. The distinctive shape that the dispersion imposes on the initial pulse is an indicator of the amount of material between us and the source, and hence an indicator of the distance to the host galaxy.

Analysis by Dr. Gajjar and the Listen team revealed 15 new pulses from FRB 121102. As well as confirming that the source is in a newly active state, the high resolution of the data obtained by the Listen instrument will allow measurement of the properties of these mysterious bursts at a higher precision than ever possible before.

The observations also show for the first time that FRBs emit at higher frequencies (with the brightest emission occurring at around 7 GHz) than previously observed. The extraordinary capabilities of the Listen backend, which is able to record several gigahertz of bandwidth at a time, split into billions of individual channels, enable a new view of the frequency spectrum of FRBs, and should shed additional light on the processes giving rise to FRB emission.

When the recently-detected pulses left their host galaxy our entire Solar System was just 2 billion years old. Life on Earth consisted of only single-celled organisms, and it would be another billion years before even the simplest multi-cellular life began to evolve. Whether or not FRBs eventually turn out to be signatures of extraterrestrial technology, Breakthrough Listen is helping to push the frontiers of a new and rapidly growing area of our understanding of the Universe around us.

The new results are reported as an Astronomer's Telegram at www.astronomerstelegram.org/?read=10675 and will be described in further detail in an upcoming scientific journal article.

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