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Diverse polarization angle swings from a repeating fast radio burst source


Fast radio bursts (FRBs) are millisecond-duration radio transients1,2 of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres3,4,5 or relativistic shocks far from the central energy source6,7,8. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters9,10 or variable polarization angles in some other apparently one-off events11,12. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks.

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Fig. 1: Polarization profiles and dynamic spectra of the seven brightest bursts from FRB 180301.
Fig. 2: RM values of seven bursts from FRB 180301.

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This work used data from FAST, a Chinese national mega-science facility, built and operated by the National Astronomical Observatories, Chinese Academy of Sciences. This work is supported by the Natural Science Foundation of China (U15311243, 11988101, 11833009, 11690024, CAS XDB23010200), the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS, the Max-Planck Partner Group, NKRDPC 2017YFA0402600 and the Youth Innovation Promotion Association of CAS (2018075).

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Authors and Affiliations



R.L. led the observational proposal 2019a-129-P in the FAST ‘Shared-Risk’ observations and the statistical analysis of repeating events. B.J.W., Y.P.M., C.F.Z. and K.J.L. developed the searching pipeline and processed the raw data to produce FRB candidates. J.C.J. conducted the polarization calibration and RM measurements. H.X. conducted the flux calibration. R.N.C. and Y.J.G. performed the timing analysis. B.Z., W.Y.W., R.X.X. and J.P. provided theoretical discussions. J.Y., M.W. and N.W. contributed to discussions on observation planning. K.J.L., J.L.H. and B.Z. organized the FRB searching team, co-supervised the data analysis and interpretations and led the writing of the paper. The search software BEAR was tested by M.Z.C., X.L.C., L.F.H., Y.X.H., J.L., Z.X.L., J.T.L., X.P., Z.G.W. and Y.H.X. FAST observations, instrument setting and monitoring was done by P.J., L.Q., H.Q.G., H.L., J.H.S., J.Y., D.J.Y. and Y.Z. All authors contributed to the analysis or interpretation of the data and to the final version of the manuscript.

Corresponding authors

Correspondence to K. J. Lee, J. L. Han or B. Zhang.

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The authors declare no competing interests.

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Peer review information Nature thanks Jason Hessels and Victoria Kaspi 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 Dynamic spectra for all 15 detected bursts of FRB 180301.

a, Dedispersed pulse profile. b, Dynamic spectra for the total intensity as a function of frequency and time (with a frequency resolution 1.95 MHz per channel and a time resolution of 393.2 μs per bin). The colour bars denote the intensity S/N scaled with the off-pulse r.m.s. value. The DMaligned values in Table 1 are used to dedisperse each burst. For bursts 1–4 we plot the raw intensity because only two linear polarization channels were recorded. For the rest of the bursts, polarization calibrations were performed.

Extended Data Fig. 2 Observed and fitted Stokes parameters Q and U for linear polarization as a function of frequency.

a, c, Normalized Stokes parameter Q and fitting residuals. b, d, Normalized Stokes parameter U and fitting residuals. The amplitudes of the oscillation have been normalized using the inferred linear polarization intensity. e, Stokes parameter V normalized by the total intensity in each channel. The grey shaded frequencies are removed before fitting owing to low signal intensities, RFI or band-edge effects. The error bars denote the 68% confidence intervals. The burst number in each subplot is as in Table 1.

Extended Data Fig. 3 RM synthesis results of the seven bursts.

We calculate the RM spectrum within the range −8,000 to +8,000 rad m−2. The horizontal red shaded area denotes the 1σ interval of the baseline. The vertical red line denotes the best-fit RM value. We also show a zoom-in of the spectral peak, where the vertical orange dashed lines show the range in which the spectrum is used in peak fitting. The best-fitting Gaussian and its 68% confidence interval are indicated by the orange curve and blue shading. The vertical red lines and shading show the best-fit RM and the 68% confidence intervals. We also show the Bayesian RM, indicated by the vertical black lines and shading. The burst number in each sub-plot is defined in Table 1.

Extended Data Fig. 4 Polarimetry stability test.

a, Temporal stability test. The RM values of PSR J1915+1009 measured with the Bayesian method confirm that there is no obvious RM variation in a one-day interval. The error bars denote 68% confidence intervals. b, Off-axis polarimetry test. PSR J1915+1009 was first placed at the beam centre and then 2.6′ away from the beam centre. The RM values measured with the Bayesian method confirm that there is no apparent systematic error for the off-axis illumination. The off-axis data point has a larger error because S/N drops for those observations owing to the off-axis illumination. c, Polarization pulse profile and PA for PSR J1915+1009, observed with central illumination. d, As in c, but off-axis illumination is used. e, Polarization profile and PA with central illumination observed one day later. f, Polarization pulse profile measured with the Parkes radio telescope by Johnston & Kerr42.

Extended Data Fig. 5 The joint fitting results of the RM synthesis spectra.

a, Bursts 5, 7, 9, 10 on 6 October 2019. b, Bursts 11, 12, 13 on 7 October 2019. c, All seven bursts. The notation is the same as in Extended Data Fig. 3.

Extended Data Fig. 6 RM synthesis spectra before and after thin-screen subtraction.

The blue and orange curve are the RM synthesis intensity spectra for burst 5. The orange curve is computed after subtracting the Stokes parameters Q and U corresponding to the RM of burst 5. The orange curve is consistent with noise. This indicates a thin-screen scenario for the Faraday rotation.

Extended Data Fig. 7 Polarization profiles of seven bright bursts and their dynamic spectra.

Here we used the globally fitted RM = 543.7 ± 2.6 rad m−2 to derotate the linear polarization. The other settings are the same as in Fig. 1.

Extended Data Fig. 8 Comparison of PA swing from seven bright bursts using different DM values in dedispersion.

ad, For each burst, blue curves use individually measured DM values as in Table 1 (a), orange curves use the DM of burst 5 (b), green curves use the lowest DM (from burst 12) (c) and red curves use the highest DM (from burst 10) (d).

Extended Data Fig. 9 Posterior distribution for the burst rate inference.

a, Marginalized posterior of the burst rate. The dashed and dotted lines denote 68% and 95% confidence levels, respectively. b, Two-dimensional distribution of the posterior. The horizontal and vertical axes show the burst rate and the shape parameter of the Weibull distribution, respectively. c, Marginalized posterior for the shape parameter.

Extended Data Table 1 FAST observations of FRB 180301

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Luo, R., Wang, B.J., Men, Y.P. et al. Diverse polarization angle swings from a repeating fast radio burst source. Nature 586, 693–696 (2020).

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