Implications of a rapidly varying FRB in a globular cluster of M81

Wenbin Lu, Paz Beniamini, Pawan Kumar

Research output: Contribution to journalArticlepeer-review


A repeating source of fast radio bursts (FRBs) is recently discovered from a globular cluster of M81. Association with a globular cluster (or other old stellar systems) suggests that strongly magnetized neutron stars, which are the most likely objects responsible for FRBs, are born not only when young massive stars undergo core-collapse, but also by mergers of old white dwarfs. We find that the fractional contribution to the total FRB rate by old stellar populations is at least a few per cent, and the precise fraction can be constrained by FRB searches in the directions of nearby galaxies, both star-forming and elliptical ones. Using very general arguments, we show that the activity time of the M81-FRB source is between 104 and 106 yr, and more likely of the order of 105 yr. The energetics of radio outbursts put a lower limit on the magnetic field strength of 10$^{13}\,$G, and the spin period $\gtrsim 0.2\,$s, thereby ruling out the source being a milli-second pulsar. The upper limit on the persistent X-ray luminosity (provided by Chandra), together with the high FRB luminosity and frequent repetitions, severely constrains (or rules out) the possibility that the M81-FRB is a scaled-up version of giant pulses from Galactic pulsars. Finally, the 50-ns variability time of the FRB light curve suggests that the emission is produced in a compact region inside the neutron star magnetosphere, as it cannot be accounted for when the emission is at distances $\gtrsim 10^{10}\rm \, cm$.

Original languageEnglish
Pages (from-to)1867-1879
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Feb 2022

Bibliographical note

Funding Information:
We also thank the par- ticipants of the FRB2021 conference for their questions/comments while the work was presented. This work has been funded in part by an NSF grant AST-2009619. WL was supported by the David and Ellen Lee Fellowship at Caltech and L yman Spitzer, Jr . Fellowship at Princeton University. PB was supported by the Gordon and Betty Moore Foundation, Grant GBMF5076.

Publisher Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.


  • radio continuum: transients
  • stars: neutron


Dive into the research topics of 'Implications of a rapidly varying FRB in a globular cluster of M81'. Together they form a unique fingerprint.

Cite this