Radio waves

Mysterious fast radio bursts include lower frequency radio waves than previously detected

A burst from the periodically active repeating fast radio burst source 20180916B arrives at the LOFAR telescope. High frequency radio waves (purple) arrive earlier than low frequency radio waves (red). The inset shows an optical image of the host galaxy of the fast radio burst source and the position of the source within the host galaxy. Credit: Futselaar / ASTRON / Tendulkar

New clues discovered in a quest to unravel the astrophysical mystery.

Ever since fast radio bursts (FRBs) were first discovered more than a decade ago, scientists have wondered what might be generating these intense bursts of radio waves from outside our galaxy. In a process of gradual elimination, the field of possible explanations has narrowed as new information is gathered about FRBs – their lifespans, the frequencies of the radio waves detected, etc.

Now, a team led by researchers from McGill University and members of the Canadian CHIME Fast Radio Burst Collaboration has established that FRBs include radio waves at lower frequencies than ever detected before, a finding that redraws the boundaries for theoretical astrophysicists trying to pinpoint the source of FRBs.

“We detected fast radio bursts up to 110 MHz where previously these bursts only existed up to 300 MHz,” explained Ziggy Pleunis, postdoctoral researcher in McGill’s Department of Physics and lead author of the recently researched published in Letters from the Astrophysical Journal. “This tells us that the region around the source of the bursts must be transparent to low-frequency emissions, whereas some theories suggested that all low-frequency emissions would be absorbed immediately and could never be detected.”

The study focused on an FRB source first detected in 2018 by the CHIME radio telescope in British Columbia. Known as FRB 20180916B, the source has attracted particular attention due to its relative proximity to Earth and the fact that it emits FRBs at regular intervals.

The research team combined the capabilities of CHIME with those of another radio telescope, LOFAR, or Low Frequency Array, in the Netherlands. The joint effort not only allowed detection of the remarkably low FRB frequencies, but also revealed a consistent delay of approximately three days between the highest frequencies picked up by CHIME and the lowest reaching LOFAR.

“This systematic delay rules out explanations of periodic activity that ignore frequency dependence and thus brings us a few steps closer to understanding the origin of these mysterious bursts,” adds co-author Daniele Michilli, also a postdoctoral researcher in the Department of Physics at McGill.

Reference: “LOFAR Detection of 110–188 MHz Emission and Frequency-dependent Activity from FRB 20180916B” by Z. Pleunis, D. Michilli, CG Bassa, JWT Hessels, A. Naidu, BC Andersen, P. Chawla, E. Fonseca, A. Gopinath, VM Kaspi, VI Kondratiev, DZ Li, M. Bhardwaj, PJ Boyle, C. Brar, T. Cassanelli, Y. Gupta, A. Josephy, R. Karuppusamy, A. Keimpema, F. Kirsten, C. Leung, B. Marcote, KW Masui, R. Mckinven, BW Meyers, C. Ng, K. Nimmo, Z. Paragi, M. Rahman, P. Scholz, K. Shin, KM Smith, IH Stairs and SP Tendulkar, 9 April 2021, Letters from the Astrophysical Journal.
DOI: 10.3847/2041-8213/abec72

About the CHIME Fast Radio Burst Collaboration

CHIME/FRB is a collaboration of over 50 scientists led by the University of British Columbia, McGill University, University of Toronto, Perimeter Institute for Theoretical Physics and the National Research Council of Canada (NRC) . The telescope is located in the mountains of British Columbia’s Okanagan Valley at the NRC Dominion Radio Astrophysical Observatory near Penticton. CHIME is an official Square Kilometer Array (SKA) route finding facility.

The research was funded by the Canada Foundation for Innovation and the governments of British Columbia, Ontario and Quebec, with additional funding from the Dunlap Institute for Astronomy and Astrophysics, the Council of natural science and engineering research and the Canadian Institute for Advanced Research.