Using the Low-Frequency Array (LOFAR), astronomers from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) have found that fast radio bursts include radio waves at frequencies lower than ever detected before.
A burst from FRB 180916 arrives at the LOFAR telescope; the higher frequency radio waves (purple) arrive earlier than the lower frequency radio waves (red); the inset shows an optical image from the host galaxy of the fast radio burst source and the position of the source in the host galaxy. Image credit: D. Futselaar / S.P. Tendulkar / ASTRON.
Fast radio bursts (FRBs) are mysterious bursts of energy from space. They have durations of milliseconds and exhibit the characteristic dispersion sweep of radio pulsars.
These events emit as much energy in one millisecond as the Sun emits in 10,000 years, but the physical phenomenon that causes them is unknown.
To date, more than one hundred FRBs have been detected, yet only some of these have so far been observed to repeat.
A research team led by McGill University astronomer Ziggy Pleunis focused on FRB 180916.J0158+65 (FRB 180916 for short), a well-studied repeating FRB.
First detected in 2018 by the CHIME radio telescope, the source is approximately 500 million light-years away. It has revealed many clues about its nature, including a 16.3 day periodicity in its activity.
Using LOFAR at 110-188 MHz, Dr. Pleunis and colleagues detected 18 bursts from FRB 180916 — by far the lowest-frequency detections of any FRB to date.
Some bursts are seen down to the lowest observed frequency of 110 MHz, suggesting that their spectra extend even lower.
“We detected fast radio bursts down to 110 MHz where before these bursts were only known to exist down to 300 MHz,” Dr. Pleunis said.
“This tells us that the region around the source of the bursts must be transparent to low-frequency emission, whereas some theories suggested that all low-frequency emission would be absorbed right away and could never be detected.”
The astronomers also revealed a consistent delay of around three days between FRB 180916’s higher frequencies picked up by CHIME and the lower ones reaching LOFAR.
“This systematic delay rules out explanations for the periodic activity that do not allow for the frequency dependence and thus brings us a few steps closer to understanding the origin of these mysterious bursts,” said Dr. Daniele Michilli, a postdoctoral researcher at McGill University.
“At different times we see radio bursts with different radio frequencies,” said Dr. Jason Hessels, an astronomer at ASTRON and the University of Amsterdam.
“Possibly the FRB is part of a binary star. If so, we would have a different view at different times of where these enormously powerful bursts are generated.”
The results were published in the Astrophysical Journal Letters.
_____
Z. Pleunis et al. 2021. LOFAR Detection of 110-188 MHz Emission and Frequency-dependent Activity from FRB 20180916B. ApJL 911, L3; doi: 10.3847/2041-8213/abec72
