A fast radio burst with submillisecond quasi-periodic structure

Abstract

Fast radio bursts (FRBs) are extragalactic radio transients of extraordinary luminosity. Studying the diverse temporal and spectral behaviour recently observed in a number of FRBs may help to determine the nature of the entire class. For example, a fast spinning or highly magnetised neutron star (NS) might generate the rotation-powered acceleration required to explain the bright emission. Periodic, subsecond components suggesting such rotation were recently reported in one FRB, and may also exist in two more. Here we report the discovery of FRB 20201020A with Apertif, an FRB that shows five components regularly spaced by 0.411 ms. This submillisecond structure in FRB 20201020A carries important clues about the progenitor of this FRB specifically, and potentially about the progenitors of FRBs in general. We therefore contrast its features to what is seen in other FRBs and pulsars, and to the predictions of some FRB models. We present a timing analysis of the FRB 20201020A components carried out in order to determine the significance of the periodicity. We compare these against the timing properties of the previously reported CHIME FRBs with subsecond quasi-periodic components, and against two Apertif bursts from repeating FRB 20180916B, which show complex time-frequency structure. We find the periodicity of FRB 20201020A to be marginally significant at 2.4σ. Its repeating subcomponents cannot be explained as pulsar rotation because the required spin rate of over 2 kHz exceeds the limits set by typical NS equations of state and observations. The fast periodicity is also in conflict with a compact object merger scenario. However, these quasi-periodic components could be caused by equidistant emitting regions in the magnetosphere of a magnetar. The submillisecond spacing of the components in FRB 20201020A, the smallest observed so far in a one-off FRB, may rule out both a NS spin period and binary mergers as the direct source of quasi-periodic FRB structure.

Quasi-periodic sub-pulse structure as a unifying feature for radio-emitting neutron stars

“…In this work, we show that this quasi-periodic substructure is detectable in members of all subclasses of radio-emitting neutron stars, especially in radio-loud magnetars, and that the previously observed dependence of substructure quasi-periodicity on rotational period is still obeyed. This may support attempts 23,25,30 to potentially infer underlying rotational periods from FRBs, if they were indeed emitted by extra-galactic magnetars. More importantly, however, the observation provides a unifying feature that links the radio emission of members in all subclasses of radio-emitting neutron stars.…”

“…However, an attempt to find a periodicity between 1 ms and 1,000 s, for instance, in hundreds of bursts from FRB 20121102A has not been successful 22 . In contrast, on sub-burst timescales, quasi-periodic substructure was reported [23][24][25] for several bursts from FRBs, though we note that the significance of some detections has been questioned 25 . Such FRB sub-burst structure has been likened to quasi-periodic 'micropulses' seen in radio pulsars (for example, ref.…”

The Curious Case of Twin Fast Radio Bursts: Evidence for Neutron Star Origin?

“…The existence of two near-identical FRBs does not imply that all FRBs have similar origins. Some FRBs have been observed to exhibit quasi-periodicity, which does not appear to be related to a spin period (Chime/Frb Collaboration et al 2022;Pastor-Marazuela et al 2023). Observations of pulsars and magnetars have shown that quasi-periodic temporal structures can originate with frequencies orders of magnitude higher than the spin period (e.g., Kramer et al 2023), but such bursts present very differently in the polarization domain, showing flat PA curves in stark contrast to FRB 20210912A and FRB 20181112A.…”

Deep Synoptic Array Science: First FRB and Host Galaxy Catalog

“…The nature of the source (or sources) that make FRBs is not known yet. Several hundred bursts have been detected (CHIME/FRB Collaboration et al 2021), some of which repeat stochastically (Chime/FRB Collaboration et al 2023) and some of which burst with quasiperiodic patterns over a wide range of timescales (Chime/ FRB Collaboration et al 2020a;Pastor-Marazuela et al 2023). Polarimetric measurements have identified dynamic, highly magnetized plasma in the parsec-scale environments of some FRB sources (Anna-Thomas et al 2023;Mckinven et al 2023).…”