We analyze the slow periodicities identified in burst sequences from FRB 121102 and FRB 180916 with periods of about 16 and 160 days, respectively, while also addressing the absence of any fast periodicity that might be associated with the spin of an underlying compact object. Both phenomena can be accounted for by a young, highly magnetized, precessing neutron star that emits beamed radiation with significant imposed phase jitter. Sporadic narrow-beam emission into an overall wide solid angle can account for the necessary phase jitter, but the slow periodicities with 25%–55% duty cycles constrain beam traversals to be significantly smaller. Instead, phase jitter may result from variable emission altitudes that yield large retardation and aberration delays. A detailed arrival time analysis for triaxial precession includes wobble of the radio beam and the likely larger, cyclical torque resulting from the changes in the spin–magnetic moment angle. These effects will confound identification of the fast periodicity in sparse data sets longer than about a quarter of a precession cycle unless fitted for and removed as with orbital fitting. Stochastic spin noise, likely to be much larger than in radio pulsars, may hinder detection of any fast periodicity in data spans longer than a few days. These decoherence effects will dissipate as sources of fast radio bursts age, so they may evolve into objects with properties similar to Galactic magnetars.
We show that the 216.8 ± 0.1 ms periodicity reported for the fast radio burst (FRB) 20191221A is very constraining for burst models. The high accuracy of burst periodicity (better than one part in 103), and the 2 per cent duty cycle (ratio of burst duration and interburst interval), suggest a pulsar-like rotating beam model for the observed activity; the radio waves are produced along open field lines within ∼107 cm of the neutron star surface, and the beam periodically sweeps across the observer as the star spins. According to this picture, FRB 20191221A is a factor ∼1012 scaled up version of galactic pulsars with one major difference, whereas pulsars convert rotational kinetic energy to EM waves and the outbursts of 20191221A require conversion of magnetic energy to radiation.
more » « less- Award ID(s):
- 2009619
- NSF-PAR ID:
- 10392050
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 519
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 5345-5351
- Size(s):
- ["p. 5345-5351"]
- Sponsoring Org:
- National Science Foundation
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