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# Detection of two bright radio bursts from magnetar SGR 1935 + 2154

## Abstract

Fast radio bursts are millisecond-duration, bright radio signals (fluence 0.1–100 Jy ms) emitted from extragalactic sources of unknown physical origin. The recent CHIME/FRB and STARE2 detection of an extremely bright (fluence ~MJy ms) radio burst from the Galactic magnetar SGR 1935+2154 supports the hypothesis that (at least some) fast radio bursts are emitted by magnetars at cosmological distances. In follow-up observations totalling 522.7 h on source, we detect two bright radio bursts with fluences of 112 ± 22 Jy ms and 24 ± 5 Jy ms, respectively. Both bursts appear to be affected by interstellar scattering and we measure significant linear and circular polarization for the fainter burst. The bursts are separated in time by ~1.4 s, suggesting a non-Poissonian, clustered emission process—similar to those seen in some repeating fast radio bursts. Together with the burst reported by CHIME/FRB and STARE2, as well as a much fainter burst seen by FAST (fluence 60 mJy ms), our observations demonstrate that SGR 1935+2154 can produce bursts with apparent energies spanning roughly seven orders of magnitude, and that the burst rate is comparable across this range. This raises the question of whether these four bursts arise from similar physical processes, and whether the fast radio burst population distribution extends to very low energies (~1030 erg, isotropic equivalent).

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## Data availability

The data that support the plots within this paper and other findings of this study are available from https://doi.org/10.5281/zenodo.4044453 or from the corresponding author upon reasonable request.

## Code availability

The pipeline written to process the baseband data can be found at https://github.com/pharaofranz/frb-baseband, while the code used to calculate the posterior distribution and generate Fig. 3 can be found at https://github.com/MJastro95. jive5ab can be retrieved from https://github.com/jive-vlbi/jive5ab, Heimdall is hosted at https://sourceforge.net/projects/heimdall-astro/ and FETCH can be found at https://github.com/devanshkv/fetch. The pulsar package DSPSR is hosted at https://sourceforge.net/projects/dspsr/, while SIGPROC was retrieved from https://github.com/SixByNine/sigproc.

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## Acknowledgements

We thank R. Blaauw and P. van Dijk for scheduling and running the observations at Westerbork. At Onsala we acknowledge the help of E. Varenius with running the observations at X-band on the Onsala 20 m telescope and we thank M. Mickaliger for helping with the initial set-up for running FETCH. We appreciate the help of N. Degenaar with interpreting the X-ray observations and we are indebted to A. Keimpema, who modified SFXC to our needs. We also thank G. Younes for useful discussions; and we thank S. Kulkarni, V. Ravi, W. Majid, J. Katz, A. Tohuvavohu and B. Grossan for helpful comments. F.K. acknowledges support by the Swedish Research Council. J.v.d.E. is supported by the Netherlands Organisation for Scientific Research (NWO). Research at the University of Amsterdam and ASTRON is supported by an NWO Vici grant to J.W.T.H. This work is based in part on observations carried out using the 32 m radio telescope operated by the Institute of Astronomy of the Nicolaus Copernicus University in Toruń (Poland) and supported by a Polish Ministry of Science and Higher Education SpUB grant.

## Author information

Authors

### Contributions

F.K. wrote and ran the search pipeline, led the observations at Onsala, interpreted the data and led the paper writing. M.P.S. ran the scattering analysis, created Figs. 1–4 and Extended Data Fig. 1, and populated Supplementary Table 1. M.J. performed the Weibull analysis and wrote the associated sections. M.P.S. and M.J. co-led the Westerbork observing campaign. K.N. ran the polarization analysis, created Extended Data Fig. 2, and wrote the respective sections. J.v.d.E. searched and analysed the X-ray observations, wrote the respective sections and populated Supplementary Table 2. J.W.T.H interpreted the data scientifically, supervised student work and wrote parts of the manuscript. M.P.G. led the observations at Toruń and wrote the section describing those data. J.Y. supported the observations at Onsala and also interpreted the data.

### Corresponding author

Correspondence to F. Kirsten.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks George Younes and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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## Extended data

### Extended Data Fig. 1 Overview of the observations of SGR 1935+2154 during this campaign.

Panels (a) and (b) both span 33 days, with observations colourcoded by observing frequency. Note the gap of 25 days between (a) and (b). No observations were conducted during that time period. Vertical lines indicate the times of reported bursts. Solid line: events found in our campaign; long-dashed: CHIME and STARE2 detections53,54; dotted: detection by FAST14; dash-dotted: X-ray bursts as reported by α) Ursi et al.65, β) Hurley et al.32 and Verrecchia et al.74, γ) a Fermi/GBM trigger on 2020 May 20 at 21:47:07.548 UT. During X-ray events β) and γ) no radio counterparts were found in any of our data, which allows us to place upper limits on the fluences — as listed in Table 1. Unfortunately we can draw no conclusions from our data coincident with event α) because Wb was in a recording gap and O8 was affected by strong RFI.

### Extended Data Fig. 2 The polarisation position angle swing (panels a and b) and average polarisation profiles (panels c and d) of PSR J1935+1616.

Shown are Stokes I (black), linear polarisation (red) and circular polarisation (blue). For comparison, the pulsar profile and PPA from the literature (at 1.4 GHz63) is shown using more transparent colours. (a) and (c): before applying the leakage calibration discussed in the text and Faraday-correcting using the true rotation measure62 of the pulsar (-10.2 rad m-2), that is we are also ignoring the delay between polarisation hands. (b) and (d): The leakage calibrated data, Faraday-corrected using the RM determined using the PSRCHIVE tool rmfit, which, in essence, accounts for the delay between the polarisation hands. This illustrates the polarisation calibration used for the SGR 1935+2154 bursts. Note that the absolute value of the PPA has been shifted to visually compare our observations with the literature.

## Supplementary information

### Supplementary Information

Supplementary Tables 1 and 2.

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### Cite this article

Kirsten, F., Snelders, M.P., Jenkins, M. et al. Detection of two bright radio bursts from magnetar SGR 1935 + 2154. Nat Astron 5, 414–422 (2021). https://doi.org/10.1038/s41550-020-01246-3

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