Manchester-led team discovers 157-day cycle in enigmatic fast radio burst

The origin of fast radio bursts (FRBs), short-lived bursts of radio emission, still remains an unsolved mystery. Since their discovery in 2007, the search for the true nature of these sources has been one of the most tantalising stories in modern day astronomy.

This quest received a major boost when recently an international team of astronomers led by Dr Kaustubh Rajwade of the Jodrell Bank Centre for Astrophysics carried out a long-term monitoring programme of one FRB, known as 121102, with The University of Manchester’s Lovell Telescope, part of the UK’s SKA pathfinder instrument e-MERLIN.

Artist’s impression of an orbital modulation model where the FRB progenitor (blue) is in an orbit with a companion astrophysical object (pink).

Credit: Kristi Mickaliger

By combining the observations made with the Lovell Telescope with previously published observations, the team discovered that 121102, as well as repeating, displays a cyclical pattern. Following an active period of 90 days, 121102 then undergoes a quiescent period lasting for 67 days, with this pattern repeating every 157 days.

FRBs were initially thought to be related to one-off cataclysmic events. However, the detection of repeating FRBs has thrown this into question, and it has been suggested these could result from precession of the magnetic axis of highly magnetized neutron stars. The detection of a 157-day cyclical pattern for 121102 however, would be hard to explain in terms of precession.

“We suggest it may instead be linked to the orbital motion of the FRB source around a massive star, a neutron star or even a black hole,” explains Dr Rajwade. “It’s only the second time we observe a periodic behaviour in an FRB. That’s significant and will help us understand how FRBs actually work!,” says SKAO Project Scientist Dr Evan Keane, member of the team behind the observations.

Support for Dr Rajwade’s discovery has recently been provided by a multi-wavelength campaign led by a team at the Max Planck Institute for Radio Astronomy. In a preprint paper, uploaded to arXiv, they report the detection of bursts from 121102 during August 2020 with a cyclical period of 161 +/- 5 days. In addition, a team from the National Astronomical Observatories of China have very recently detected bursts from 121102 in the predicted active period thus lending credence to the periodicity claim, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), another SKA pathfinder, in a paper published in the Monthly Notices of the Royal Astronomical Society.

By Hilary Kay (The University of Manchester)

It's only the second time we observe a periodic behaviour in an FRB. That's significant and will help us understand how FRBs actually work!

SKAO Project Scientist Dr Evan Keane