Fast radio bursts are bright, unresolved, non-repeating, broadband, millisecond flashes, found primarily at high Galactic latitudes, with dispersion measures much larger than expected for a Galactic source1, 2, 3, 4, 5, 6, 7. The inferred all-sky burst rate8 is comparable to the core-collapse supernova rate9 out to redshift 0.5. If the observed dispersion measures are assumed to be dominated by the intergalactic medium, the sources are at cosmological distances with redshifts of 0.2 to 1 (refs 10 and 11). These parameters are consistent with a wide range of source models12, 13, 14, 15, 16, 17. One fast burst6 revealed circular polarization of the radio emission, but no linear polarization was detected, and hence no Faraday rotation measure could be determined. Here we report the examination of archival data revealing Faraday rotation in the fast radio burst FRB 110523. Its radio flux and dispersion measure are consistent with values from previously reported bursts and, accounting for a Galactic contribution to the dispersion and using a model of intergalactic electron density10, we place the source at a maximum redshift of 0.5. The burst has a much higher rotation measure than expected for this line of sight through the Milky Way and the intergalactic medium, indicating magnetization in the vicinity of the source itself or within a host galaxy. The pulse was scattered by two distinct plasma screens during propagation, which requires either a dense nebula associated with the source or a location within the central region of its host galaxy. The detection in this instance of magnetization and scattering that are both local to the source favours models involving young stellar populations such as magnetars over models involving the mergers of older neutron stars, which are more likely to be located in low-density regions of the host galaxy.
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Extended data figures and tables
Extended Data Figures
- Extended Data Figure 1: Events in frequency–time and DM–time space. (329 KB)
From left to right are shown data for FRB 110523, a simulated FRB, a known pulsar PSR J2257+5909, and man-made radio frequency interference (RFI). Brightness temperature is shown in frequency–time space (upper panels) and the same data in DM–time space (lower panels). The relative dispersion measure is the difference between the DM and the event DM; event DM values are 622.8 pc cm−3, 610.3 pc cm−3, 151.0 pc cm−3 and 1132.1 pc cm−3 from left to right. The time axes of the frequency–time plots show time relative to the zero time in DM–time space. The colour scale in the lower panels represents broadband flux, with red showing a bright source.
- Extended Data Figure 2: Pulse profiles for FRB 110523 in three sub-bands. (182 KB)
Each sub-band has width of 66 MHz. The pulse width decreases with frequency (at 2.6σ significance), consistent with models of scattering in the interstellar medium. Also shown in black is the best-fit model profile for the middle band.
- Extended Data Figure 3: Spectral brightness correlation function of FRB 110523. (55 KB)
The intensity spectrum has structure that is correlated for frequency separations less than fdc = 1.2 MHz. Error bars are the standard deviation of 3,268 simulated measurements with 817 independent noise realizations and are correlated.