Magnetar spin-down glitch clearing the way for FRB-like bursts and a pulsed radio episode

Magnetars are a special subset of the isolated neutron star family, with X-ray and radio emission mainly powered by the decay of their immense magnetic fields. Many attributes of magnetars remain poorly understood: spin-down glitches or the sudden reductions in the star’s angular momentum, radio bursts reminiscent of extragalactic fast radio bursts (FRBs) and transient pulsed radio emission lasting months to years. Here we unveil the detection of a large spin-down glitch event (fractional change in spin frequency |Δν/ν|=5.8+2.6−1.6×10−6) from the magnetar SGR 1935+2154 on 5 October 2020 (±1 day). We find no change to the source-persistent surface thermal or magnetospheric X-ray behaviour, nor is there evidence of strong X-ray bursting activity. Yet, in the subsequent days, the magnetar emitted three FRB-like radio bursts followed by a month-long episode of pulsed radio emission. Given the rarity of spin-down glitches and radio signals from magnetars, their approximate synchronicity suggests an association, providing pivotal clues to their origin and triggering mechanisms with ramifications to the broader magnetar and FRB populations. We postulate that impulsive crustal plasma shedding close to the magnetic pole generates a wind that combs out magnetic field lines, rapidly reducing the star’s angular momentum while temporarily altering the magnetospheric field geometry to permit the pair creation needed to precipitate radio emission.A portion of this work was supported by NASA through the NICER mission and the Astrophysics Explorers Program. G.Y.’s research is supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Oak Ridge Associated Universities under contract with NASA. M.G.B. acknowledges the support of the National Science Foundation through grant AST-1813649. A.B.P. is a McGill Space Institute (MSI) Fellow and a Fonds de Recherche du Quebec–Nature et Technologies (FRQNT) postdoctoral fellow. S.G. acknowledges the support of the Centre National d’Etudes Spatiales (CNES). T.E. acknowledges Hakubi projects of Kyoto University and RIKEN, and is supported by JSPS/ MEXT KAKENHI grant numbers 15H00845 and 17K18776. W.C.G.H. acknowledges support through grant 80NSSC22K0397 from NASA. A.B. is supported by a Juan de la Cierva fellowship. C.-P.H. acknowledges support from the Ministry of Science and Technology in Taiwan through grant MOST 109-2112-M-018-009-MY3. W.A.M acknowledges support from the Jet Propulsion Laboratory, California Institute of Technology, under a Research and Technology Development Grant through a contract with NASA. US government sponsorship is acknowledged.Peer reviewe