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Astronomers trace radio burst to its home galaxy

by Juanita Bawagan Feb 13 / 17

Astronomers have pinpointed the source of a series of mysterious cosmic signals to a distant dwarf galaxy 3 billion light years away. This discovery marks the first time scientists have been able to trace the signals to a specific location in the sky and offers new ways to study what is causing them.

Fast radio bursts (FRBs) have captivated the attention of researchers in the CIFAR Cosmology & Gravity program since their discovery in 2007. FRBs last only a few thousandths of a second but are far brighter and more powerful than any known short flashes, such as pulses from radio pulsars, a form of neutron star. FRBs’ brief nature combined with technological constraints have made them difficult to detect.

Now, researchers have zeroed in on the location of one of 18 known FRBs using a network of telescopes and special imaging and timing technologies. Associate Fellow Scott Ransom (National Radio Astronomy Observatory) and R. Howard Webster Foundation Fellow Victoria Kaspi (McGill University) were part of the scientific team that published their findings in Nature with companion papers in The Astrophysical Journal Letters.

“We finally know at least one of these is coming from another galaxy at a very far distance,” says Ransom from NRAO headquarters in Charlottesville, VA.

A composite image of FRB 121102, which astronomers identified as the source of bursts of radio waves.(Credit: Gemini Observatory/AURA/NSF/NRC)

Previously, FRBs could be traced to a region in the sky, but not to any of the hundreds or even thousands of galaxies within that region. In order to narrow this scope, scientists used the Very Large Array (VLA), a multi-antenna radio telescope system, to produce a high-definition image of the sky. They focused on a particular FRB that the more sensitive Arecibo telescope had detected earlier and which had been shown to be the only known repeater.

“What really surprised us with the first burst we saw at the VLA is that it was whopping bright,” Ransom recalls.  “After watching it for several months, it started bursting brightly and often in the fall.”

The FRB that was located has led to many astronomical firsts. FRB121102 was discovered Nov. 2, 2012 in the Arecibo Pulsar ALFA survey. It was the first FRB that was not detected by the Parkes radio telescope in Australia, which addressed concerns that previous bursts may have been technological or environmental flukes. In 2016, the same team including Ransom, Kaspi and Senior Fellow Ingrid Stairs (University of British Columbia), detected 10 additional bursts coming from FRB121102. This made it the first repeating fast radio burst and largely ruled out the possibility that it was caused by a cataclysmic event like the creation of a black hole. Now, scientists believe the source likely involves a young neutron star, possibly a highly-magnetic magnetar.

After years of research, Ransom is happy to see FRB121102 is no longer being misidentified as a strange object in our galaxy.

“This FRB is the one people thought was the oddball but it is now unambiguously at far distances, unambiguously coming from another galaxy,” says Ransom.

“That makes you wonder that if this one has been promoted to the gold standard, have we missed other FRBs? Maybe they’re all repeating and we just haven’t been lucky.”

That question is a point of active research for Ransom and many other astronomers.

“There is still a lot of work to do to unravel the mystery surrounding FRBs,” Kaspi said. “But identifying the host galaxy for this repeating FRB marks a big step toward solving the puzzle.”

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) could help answer remaining questions, she notes. The all-Canadian initiative involves a number of CIFAR researchers and is based in B.C. Although the radio telescope was designed to study how the universe assembled itself, CHIME is also an ideal tool for detecting FRBs. Kaspi is the principal investigator for the CHIME extension which will be used to study transient radio signals.

Once CHIME comes online in the spring, it will measure more than half of the sky each day as the Earth turns. CHIME could potentially detect as many FRBs in a day as previous telescopes have detected over the last decade.

“Once we understand the origin of this phenomenon, it could provide us with a new and valuable probe of the universe,” Kaspi said.

A direct localization of a fast radio burst and its host” was published in Nature on Jan. 5, 2017.