A unified picture of Galactic and cosmological fast radio bursts
ABSTRACT The discovery of a fast radio burst (FRB) in our Galaxy associated with a magnetar (neutron star with strong magnetic field) has provided a critical piece of information to help us finally understand these enigmatic transients. We show that the volumetric rate of Galactic-FRB like events is consistent with the faint end of the cosmological FRB rate, and hence they most likely belong to the same class of transients. The Galactic FRB had an accompanying X-ray burst, but many X-ray bursts from the same object had no radio counterpart. Their relative rates suggest that for every FRB there are roughly 102–103 X-ray bursts. The radio light curve of the Galactic FRB had two spikes, separated by 30 ms in the 400–800 MHz frequency band. This is an important clue and highly constraining of the class of models where the radio emission is produced outside the light cylinder of the magnetar. We suggest that magnetic disturbances close to the magnetar surface propagate to a distance of a few tens of neutron star radii where they damp and produce radio emission. The coincident hard X-ray spikes associated with the two FRB pulses seen in this burst and the flux ratio between the two more »
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Award ID(s):
Publication Date:
NSF-PAR ID:
10269531
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
498
Issue:
1
Page Range or eLocation-ID:
1397 to 1405
ISSN:
0035-8711
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 frommore »