A fast radio burst with submillisecond quasi-periodic structure

¹ Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
e-mail: ines.pastor.marazuela@gmail.com
² ASTRON, The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
³ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
⁴ Cahill Center for Astronomy, California Institute of Technology, Pasadena, CA, USA
⁵ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, 411007 Maharashtra, India
⁶ Netherlands eScience Center, Science Park 140, 1098 XG Amsterdam, The Netherlands
⁷ Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada
⁸ NYU Abu Dhabi, PO Box 129188 Abu Dhabi, United Arab Emirates
⁹ Center for Astro, Particle, and Planetary Physics (CAP 3), NYU Abu Dhabi, PO Box 129188 Abu Dhabi, United Arab Emirates
¹⁰ Kapteyn Astronomical Institute, PO Box 800 9700 AV Groningen, The Netherlands
¹¹ Astronomisches Institut der Ruhr-Universität Bochum (AIRUB), Universitätsstrasse 150, 44780 Bochum, Germany
¹² Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹³ Department of Physics, Virginia Polytechnic Institute and State University, 50 West Campus Drive, Blacksburg, VA 24061, USA
¹⁴ CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76 Epping, NSW 1710, Australia
¹⁵ Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia
¹⁶ University of Oslo Center for Information Technology, PO Box 1059 0316 Oslo, Norway

Received: 16 February 2022
Accepted: 3 August 2023

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.