# A fast radio burst associated with a Galactic magnetar

## Abstract

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 FRBs3,4. 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 burst9,10,11 favours emission models that describe synchrotron masers or electromagnetic pulses powered by magnetar bursts and giant flares3,4,12,13. The discovery of FRB 200428 implies that active magnetars such as SGR 1935+2154 can produce FRBs at extragalactic distances.

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## Data availability

Data are available upon request. These data are in a public archive by the Caltech Library at http://doi.org/10.22002/D1.1647 .

## Code availability

Custom code is available at https://github.com/cbochenek/STARE2-analysis. The code used to fit the burst profiles is available on request.

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## Acknowledgements

We thank the then director of OVRO, A. Readhead, for funds (derived from the Alan Moffet Funds) that allowed us to start this project. The Caltech and Jet Propulsion Laboratory President’s and Director’s Fund enabled us to build the second system at Goldstone and the third system near Delta, Utah. We are thankful to Caltech and the Jet Propulsion Laboratories for the second round of funding. C.D.B., a PhD student, was partially supported by the Heising-Simons foundation. We also thank S. Weinreb and D. Hodge for building the front-end and back-end boxes, J. Lagrange for support at GDSCC, J. Matthews and the Telescope Array Collaboration for assistance at Delta, and the entire OVRO staff, in particular J. Lamb, D. Woody and M. Catha, for support. We thank S. Phinney and W. Lu for comments on the manuscript. A portion of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This research was additionally supported by the National Science Foundation under grant AST-1836018. This research made use of Astropy, a community-developed core Python package for Astronomy. This research also used the SIMBAD database, operated at CDS, Strasbourg, France.

## Author information

Authors

### Contributions

S.R.K., C.D.B., D.L.M., V.R., K.V.B. and G.H. conceived and developed the STARE2 concept and observing strategy. C.D.B., D.L.M., K.V.B., J.K. and S.R.K. led the construction and initial deployment of STARE2. C.D.B., D.L.M., K.V.B., V.R., J.K. and G.H. designed and built the STARE2 subsystems. C.D.B., D.L.M. and K.V.B. commissioned STARE2. C.D.B. operated STARE2, performed the localization and transient rate analyses, as well as the searches for sub-threshold events and events associated with other SGR flares. V.R. extracted the properties of the burst. C.D.B. and V.R. led the writing of the manuscript with the assistance of all co-authors.

### Corresponding author

Correspondence to C. D. Bochenek.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Peer review information Nature thanks Evan Keane and Amanda Weltman for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Extended data figures and tables

### Extended Data Fig. 1 Time series and dynamic spectrum of FRB 200428 at each station.

Top, time series at each station referenced to the arrival time at OVRO at ν = 1,529.267578 MHz. Bottom, dynamic spectra at each station. The data shown in all panels were processed in the same way as those in Fig. 1. We have not corrected for the spectral response at each station. The blue bars in the Delta dynamic spectrum indicate frequencies affected by radio frequency interference that were excised from the data.

### Extended Data Fig. 2 Fits to data on FRB 200428 in four sub-bands.

Black lines indicate the raw data and blue lines show the best-fit model. The sub-band centre frequencies are indicated beside each plot.

### Extended Data Fig. 3 Volumetric rates of FRBs.

Volumetric rate, Φ(>E), calculated from the radio burst from SGR 1935+2154 (red cross) compared with the extrapolated luminosity function of bright FRBs29 (blue-shaded region). The black crosses represent the volumetric rate of FRBs determined from the ASKAP Fly’s Eye sample29. We note that correlated probabilities between the parameters of the luminosity function are not taken into account, leading to an overestimate of the uncertainty in the blue-shaded region; see ref. 43 for a similar plot in which they are taken into account. The volumetric rate was calculated by modelling the population of Galactic fast radio transients as a Poisson process and assuming that these fast radio transients track star formation. The uncertainties on this measurement are 1σ statistical uncertainties, in addition to the maximum range of possible distances to SGR 1935+2154 (4–16 kpc)39. We also show the energy of the weakest burst detected from FRB 180916.J0158+65—a repeating FRB—for comparison8. The volumetric rate of Galactic fast radio transients is consistent with extrapolating the luminosity function of bright FRBs to the energy of FRB 200428.

### Extended Data Fig. 4 Upper limits on fast radio transients from other flares of SGR 1935+2154 observable by STARE2.

The ordinate shows the 7.3σ upper limit on the fluence of a potential burst in Jy ms1/2, and the abscissa shows the times (in MJD) of reported flares from SGR 1935+2154. The derivation of the upper limits is described in Methods. We note that our three-station system was observing only during the flares between MJD 58966 and MJD 58987, shown in black. For the other flares, only our stations at OVRO and GDSCC were observing, shown in red. We show FRB 200428 in blue; the error bar represents the standard error in the measured fluence.

## Rights and permissions

Reprints and Permissions

Bochenek, C.D., Ravi, V., Belov, K.V. et al. A fast radio burst associated with a Galactic magnetar. Nature 587, 59–62 (2020). https://doi.org/10.1038/s41586-020-2872-x

• Accepted:

• Published:

• Issue Date:

• ### Double-peaked Pulse Profile of FRB 200428: Synchrotron Maser Emission from Magnetized Shocks Encountering a Density Jump

• Di Xiao
•  & Zi-Gao Dai

The Astrophysical Journal (2020)

• ### NICER View of the 2020 Burst Storm and Persistent Emission of SGR 1935+2154

• George Younes
• , Tolga Güver
• , Chryssa Kouveliotou
• , Matthew G. Baring
• , Chin-Ping Hu
• , Beste Begiçarslan
• , Teruaki Enoto
• , Ersin Göğüş
• , Lin Lin
• , Alice K. Harding
• , Alexander J. van der Horst
• , Walid A. Majid
• , Sebastien Guillot
•  & Christian Malacaria

The Astrophysical Journal (2020)

• ### The physical mechanisms of fast radio bursts

• Bing Zhang

Nature (2020)

• ### A bright millisecond-duration radio burst from a Galactic magnetar

Nature (2020)

• ### No pulsed radio emission during a bursting phase of a Galactic magnetar

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• , C. F. Zhang
• , P. Wang
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• , J. C. Jiang
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