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Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear 1 . Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin 2,3 . These two FRBs have unusually large Faraday rotation measure values 2,3 , probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source 4-8 . Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measure itself 7,9 . Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity-low Faraday rotation measure regime (<1,000 rad m -2 ). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula-or the interacting shock in a binary system-powers the persistent radio source., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Spider pulsars are millisecond pulsars in short-period (≲12-h) orbits with low-mass (~0.01-0.4 M ⊙ ) companion stars. The pulsars ablate plasma from the companion star, causing time delays and eclipses of the radio emission from the pulsar. The magnetic field of the companion has been proposed to strongly influence both the evolution of the binary system 1 and the eclipse properties of the pulsar emission 2 . Changes in the rotation measure (RM) have been seen in a spider system, implying that there is an increase in the magnetic field near the eclipse 3 . Here we report a diverse range of evidence for a highly magnetized environment in the spider system PSR B1744 - 24A 4 , located in the globular cluster Terzan 5. We observe semi-regular profile changes to the circular polarization, V, when the pulsar emission passes close to the companion. This suggests that there is Faraday conversion where the radio wave tracks a reversal in the parallel magnetic field and constrains the companion magnetic field, B  (> 10 G). We also see irregular, fast changes in the RM at random orbital phases, implying that the magnetic strength of the stellar wind, B, is greater than 10 mG. There are similarities between the unusual polarization behaviour of PSR B1744 - 24A and some repeating fast radio bursts (FRBs) 5-7 . Together with the possible binary-produced long-term periodicity of two active repeating FRBs 8,9 , and the discovery of a nearby FRB in a globular cluster 10 , where pulsar binaries are common, these similarities suggest that a proportion of FRBs have binary companions., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Fast radio bursts (FRBs) are brief, intense flashes of radio waves from unidentified extragalactic sources. Polarized FRBs originate in highly magnetized environments. We report observations of the repeating FRB 20190520B spanning 17 months, which show that the FRB's Faraday rotation is highly variable and twice changes sign. The FRB also depolarizes below radio frequencies of about 1 to 3 gigahertz. We interpret these properties as being due to changes in the parallel component of the magnetic field integrated along the line of sight, including reversing direction of the field. This could result from propagation through a turbulent magnetized screen of plasma, located 10 -5 to [Formula: see text] parsecs from the FRB source. This is consistent with the bursts passing through the stellar wind of a binary companion of the FRB source.

The polarization of fast radio bursts (FRBs), which are bright astronomical transient phenomena, contains information about their environments. Using wide-band observations with two telescopes, we report polarization measurements of five repeating FRBs and find a trend of lower polarization at lower frequencies. This behavior is modeled as multipath scattering, characterized by a single parameter, σ RM , the rotation measure (RM) scatter. Sources with higher σ RM have higher RM magnitude and scattering time scales. The two sources with the highest σ RM , FRB 20121102A and FRB 20190520B, are associated with compact persistent radio sources. These properties indicate a complex environment near the repeating FRBs, such as a supernova remnant or a pulsar wind nebula, consistent with their having arisen from young stellar populations.