A fast radio burst associated with a Galactic magnetar

Since their discovery in 2007¹, much effort has been devoted to uncovering the sources of the extragalactic, millisecond-duration fast radio bursts (FRBs)². A class of neutron stars known as magnetars is a leading candidate source of FRBs^3,4. Magnetars have surface magnetic fields in excess of 10¹⁴ gauss, the decay of which powers a range of high-energy phenomena⁵. Here we report observations of a millisecond-duration radio burst from the Galactic magnetar SGR 1935+2154, with a fluence of 1.5 ± 0.3 megajansky milliseconds. This event, FRB 200428 (ST 200428A), was detected on 28 April 2020 by the STARE2 radio array⁶ in the 1,281-1,468 megahertz band. The isotropic-equivalent energy released in FRB 200428 is 4 × 10³ times greater than that of any radio pulse from the Crab pulsar-previously the source of the brightest Galactic radio bursts observed on similar timescales⁷. FRB 200428 is just 30 times less energetic than the weakest extragalactic FRB observed so far⁸, and is drawn from the same population as the observed FRB sample. The coincidence of FRB 200428 with an X-ray burst^9-11 favours emission models that describe synchrotron masers or electromagnetic pulses powered by magnetar bursts and giant flares^3,4,12,13. The discovery of FRB 200428 implies that active magnetars such as SGR 1935+2154 can produce FRBs at extragalactic distances.