International team discover 157-day cycle in unusual Fast Radio Bursts from a distant galaxy

8 June 2020

A four-year observing campaign with the UK’s Lovell Telescope of an extraordinary source of Fast Radio Bursts – short duration bursts of radio emission thought to originate in a distant galaxy – has revealed an as yet undiscovered feature of this source. These latest findings have been published in a paper out today, 8 June 2020.

An international team led by the University of Manchester, with key contributions from the University of Oxford’s Department of Physics, have discovered that the source known as FRB 121102, has been emitting radio bursts in an approximately 90-day window, followed by a period of radio silence for around 67 days. The cycle then repeats every 157 days.

This discovery provides an important clue towards understanding the astrophysical objects and processes responsible for this emission. The detected repeating nature of this process implies it may be caused by orbital motion linked to a massive star, a neutron star or a black hole.

New aspects of nature

Professor Aris Karastergiou, who leads the Oxford group developing the capabilities of next generation telescopes in detecting Fast Radio Bursts and Pulsars, and a co-author on this paper, noted that: ‘There is always something particularly satisfying about discovering new aspects of nature. Fast Radio Bursts are now giving us more and more clues on their origin and the properties of the space they traverse.’

Dr. Kaustubh Rajwade of The University of Manchester who led the new research, said: ‘This is an exciting result as it is only the second system where we believe we see this modulation in burst activity. Detecting a periodicity provides an important constraint on the origin of the bursts and the activity cycles could argue against a precessing neutron star.’

FRBS were first discovered as recently as 2007 and were initially thought to be one-off in nature, marking some cataclysmic event. This idea was challenged with the revelation that a signal found in data taken with the Arecibo radio telescope on November 2, 2012, and known now as FRB 121102, was seen to repeat in 2016. Intriguingly these bursts did not seem to describe any discernible pattern which might help reveal the nature of the underlying source. This quest received a major boost when a global team of scientists led by researchers from The University of Manchester revealed an unexpectedly long 157-day periodicity in the bursting activity of FRB 121102.

Important discovery

Professor Benjamin Stappers from The University of Manchester, who leads the MeerTRAP project to hunt for FRBs using the MeerKAT telescope in South Africa said: ‘This result relied on the regular monitoring possible with the Lovell Telescope, and non-detections were just as important as the detections.’

Since 2016, astronomers have been carrying out an observing campaign of FRB 121102 using the 76-m Lovell radio telescope located at the Jodrell Bank Observatory, UK. Using the 32 bursts they discovered, along with the published bursts in the literature, they realised that FRB 121102 has been emitting radio bursts in a consistent repeating pattern.

In a new paper published in Monthly Notices for the Royal Astronomical Society, the team confirm that FRB 121102 is only the second repeating source of FRBs to show such periodic activity but its timescales for this activity cycle are almost 10 times longer than the 16.35 day periodicity exhibited by FRB180916.J10158+56 which was recently discovered by the CHIME telescope in Canada.

An alternative explanation for the cause of the repeating FRB is the precession of the magnetic axis of a highly magnetised, radio emitting neutron star, but with current data, scientists believe it may not be possible to explain a 157-day precession period in a star with large magnetic fields. More FRBs may be expected to show similar activity cycles.

‘This exciting discovery highlights how little we know about the origin of FRBs,’ concludes Duncan Lorimer who serves as Associate Dean for Research at West Virginia University and, along with PhD student Devansh Agarwal, helped develop the data analysis pipeline that led to the discovery. ‘Further observations of a larger sample of FRBs will provide a clearer picture of the population of these periodic sources and elucidate their origin.’