Fast Radio Burst Source Research Articles

Frb-voe: A Real-time Virtual Observatory Event Alert Service for Fast Radio Bursts

Abstract We present frb-voe, a publicly available software package that enables radio observatories to broadcast fast radio burst (FRB) alerts to subscribers through low-latency virtual observatory events (VOEvents). We describe a use case of frb-voe by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Collaboration, which has broadcast thousands of FRB alerts to subscribers worldwide. Using this service, observers have daily opportunities to conduct rapid multiwavelength follow-up observations of new FRB sources. Alerts are distributed as machine-readable reports and as emails containing FRB metadata, and are available to the public within approximately 13 s of detection. A sortable database and a downloadable JSON file containing FRB metadata from all broadcast alerts can be found on CHIME/FRB’s public webpage. The frb-voe service also provides users with the ability to retrieve FRB names from the Transient Name Server through the frb-voe client user interface. The frb-voe service can act as a foundation on which any observatory that detects FRBs can build its own VOEvent broadcasting service to contribute to the coordinated multiwavelength follow-up of astrophysical transients.

Challenges for Fast Radio Bursts as Multimessenger Sources from Binary Neutron Star Mergers

Fast radio bursts (FRBs) are millisecond-duration transients from extragalactic sources, with their origins remaining a topic of active debate. Among the proposed progenitors, binary neutron star (BNS) mergers are compelling candidates for some nonrepeating FRBs. However, associating FRBs with BNS mergers cannot be based solely on low chance coincidence probability. This study delineates necessary criteria for associating FRBs with BNS mergers, focusing on the postmerger ejecta environment. To underscore the significance of these criteria, we scrutinise the proposed association between GW190425 and FRB 20190425A, considering the requirement for the FRB signal to traverse the dense merger ejecta without significant attenuation to remain detectable at 400 MHz. Our investigation reveals that if the FRB is linked to the gravitational-wave (GW) event, the GW data support a highly off-axis configuration, with a probability of the BNS merger viewing angle p(θ v > 30°) being ≈99.99%. This strongly excludes an on-axis system, which is required for this FRB to be detectable. We also find faraway FRB emission models inadequate to explain the FRB 20190425A–GW190425 connection. Thus, we conclude that GW190425 is not related to FRB 20190425A. We discuss the implications for future multimessenger observations, suggesting that BNS merger remnants are unlikely to account for more than 1% of FRB sources. This finding implies that short gamma-ray bursts, which are expected to occur in only a fraction of all BNS mergers, cannot account for the overall characteristics of the FRB host population.

A Repeating Fast Radio Burst Source in a Low-luminosity Dwarf Galaxy

We present the localization and host galaxy of FRB 20190208A, a repeating source of fast radio bursts (FRBs) discovered using CHIME/FRB. As part of the Pinpointing REpeating ChIme Sources with EVN dishes repeater localization program on the European VLBI Network (EVN), we monitored FRB 20190208A for 65.6 hr at ∼1.4 GHz and detected a single burst, which led to its very long baseline interferometry localization with 260 mas uncertainty (2σ). Follow-up optical observations with the MMT Observatory (i ≳ 25.7 mag (AB)) found no visible host at the FRB position. Subsequent deeper observations with the Gran Telescopio Canarias, however, revealed an extremely faint galaxy (r = 27.32 ± 0.16 mag), very likely (99.95%) associated with FRB 20190208A. Given the dispersion measure of the FRB (∼580 pc cm−3), even the most conservative redshift estimate ( zmax∼0.83 ) implies that this is the lowest-luminosity FRB host to date (≲108 L ⊙), even less luminous than the dwarf host of FRB 20121102A. We investigate how localization precision and the depth of optical imaging affect host association and discuss the implications of such a low-luminosity dwarf galaxy. Unlike the other repeaters with low-luminosity hosts, FRB 20190208A has a modest Faraday rotation measure of a few tens of rad m−2, and EVN plus Very Large Array observations reveal no associated compact persistent radio source. We also monitored FRB 20190208A for 40.4 hr over 2 yr as part of the Extragalactic Coherent Light from Astrophysical Transients repeating FRB monitoring campaign on the Nançay Radio Telescope and detected one burst. Our results demonstrate that, in some cases, the robust association of an FRB with a host galaxy will require both high localization precision and deep optical follow-up.

Multiwavelength constraints on the origin of a nearby repeating fast radio burst source in a globular cluster

Multiwavelength constraints on the origin of a nearby repeating fast radio burst source in a globular cluster

Constraining the Hubble constant with scattering in host galaxies of fast radio bursts

Measuring the Hubble constant ($ H $) is one of the most important missions in astronomy. Nevertheless, recent studies exhibit differences between the employed methods. Fast radio bursts (FRBs) are coherent radio transients with large dispersion measures (DM) with a duration of milliseconds. DM$_ IGM $, the free electron column density along a line of sight in the intergalactic medium (IGM), could open a new avenue for probing $ H $. However, it has been challenging to separate DM contributions from different components (i.e., the IGM and the host galaxy plasma), and this hampers the accurate measurements of DM$_ IGM $ and hence $ H $. We adopted a method to overcome this problem by using the temporal scattering of the FRB pulses due to the propagation effect through the host galaxy plasma (scattering time). The scattering-inferred DM in a host galaxy improves the estimate of DM$_ IGM $, which in turn leads to a better constraint on $ H $. In previous studies, a certain value or distribution has conventionally been assumed of the dispersion measure in host galaxies (DM$_ h $). We compared this method with ours by generating 100 mock FRBs, and we found that our method reduces the systematic (statistical) error of H$_0$ by 9.1$<!PCT!>$ (1$<!PCT!>$) compared to the previous method. We applied our method to 30 localized FRB sources with both scattering and spectroscopic redshift measurements to constrain H$_0$. Our result is H$_0$ = 74$_ $ km s$^ $ Mpc$^ $, where the central value prefers the value obtained from local measurements over the cosmic microwave background. We also measured DM$_ h $ with a median value of $103^ $ pc cm$^ The $ DM_h $ had to be assumed in previous works to derive DM$_ IGM $. Scattering enables us to measure $ IGM $ without assuming DM$_ h $ to constrain H$_0$. The reduction in systematic error is comparable to the Hubble tension ($ Combined with the fact that more localized FRBs will become available, our result indicates that our method can be used to address the Hubble tension using future FRB samples.

Preferential occurrence of fast radio bursts in massive star-forming galaxies.

Fast radio bursts (FRBs) are millisecond-duration events detected from beyond the Milky Way. FRB emission characteristics favour highly magnetized neutron stars, or magnetars, as the sources1, as evidenced by FRB-like bursts from a galactic magnetar2,3, and the star-forming nature of FRB host galaxies4,5. However, the processes that produce FRB sources remain unknown6. Although galactic magnetars are often linked to core-collapse supernovae (CCSNe)7, it is uncertain what determines which supernovae result in magnetars. The galactic environments of FRB sources can be used to investigate their progenitors. Here, we present the stellar population properties of 30 FRB host galaxies discovered by the Deep Synoptic Array (DSA-110). Our analysis shows a marked deficit of low-mass FRB hosts compared with the occurrence of star formation in the Universe, implying that FRBs are a biased tracer of star formation, preferentially selecting massive star-forming galaxies. This bias may be driven by galaxy metallicity, which is positively correlated with stellar mass8. Metal-rich environments may favour the formation of magnetar progenitors through stellar mergers9,10, as higher-metallicity stars are less compact and more likely to fill their Roche lobes, leading to unstable mass transfer. Although massive stars do not have convective interiors to generate strong magnetic fields by dynamo11, merger remnants are thought to have the requisite internal magnetic-field strengths to result in magnetars11,12. The preferential occurrence of FRBs in massive star-forming galaxies suggests that a core-collapse supernova of merger remnants preferentially forms magnetars.

Damping of Strong GHz Waves near Magnetars and the Origin of Fast Radio Bursts

We investigate how a fast radio burst (FRB) emitted near a magnetar would propagate through its surrounding dipole magnetosphere at radii r = 107–109 cm. First, we show that a GHz burst emitted in the O-mode with luminosity L ≫ 1040 erg s−1 is immediately damped for all propagation directions except a narrow cone along the magnetic axis. Then, we examine bursts in the X-mode. GHz waves propagating near the magnetic equator behave as magnetohydrodynamic (MHD) waves if they have L ≫ 1040 erg s−1. The waves develop plasma shocks in each oscillation and dissipate at r∼3×108L42−1/4 cm. Waves with lower L or propagation directions closer to the magnetic axis do not obey MHD. Instead, they interact with individual particles and require a kinetic description. The kinetic interaction quickly accelerates particles to Lorentz factors 104–105 at the expense of the wave energy, which again results in strong damping of the wave. In either propagation regime, MHD or kinetic, the dipole magnetosphere surrounding the FRB source acts as a pillow absorbing the radio burst and reradiating the absorbed energy in X-rays. These results constrain the origin of observed FRBs. We argue that the observed FRBs avoid damping because they are emitted by relativistic outflows from magnetospheric explosions, so that the GHz waves do not need to propagate through the outer equilibrium magnetosphere surrounding the magnetar.

Selection bias obfuscates the discovery of fast radio burst sources.

Fast radio bursts (FRBs) are a newly discovered class of extragalactic radio transients characterized by their high energy and short duration (from microseconds to milliseconds)1. The physical origin of these FRBs remains unknown and is a subject of ongoing research, with magnetars emerging as leading candidates2,3. Previous studies have used various methodologies to address the problem of FRB origin, including demographic analyses of FRB host galaxies and their local environments4-6, assessments of FRB rate evolution with redshift7-9 and searches for proposed multi-messenger FRB counterparts10. However, these studies are susceptible to substantial biases stemming from unaccounted radio and optical selection effects. Here we present empirical evidence for a substantial selection bias against detecting FRBs in galaxies with large inclination angles (edge-on) using a sample of hosts identified for FRBs discovered by untargeted surveys. This inclination-related bias probably leads to a significant underestimation (by about a factor of two) of the FRB rates reported in the literature and disfavours globular clusters as the dominant origin of FRB sources, as previously speculated6. These conclusions have important implications for FRB progenitor models and targeted FRB follow-up strategies. We further investigate the impact of this bias on the relative rate of FRBs in different host environments. Our analysis suggests that scattering in FRB hosts is probably responsible for the observed bias11,12. However, a larger sample of localized FRBs is required to robustly quantify the contribution of scattering to the inclination-related selection bias.

Statistical Properties and Cosmological Applications of Fast Radio Bursts

Abstract Fast radio burst (FRB) is a type of extragalactic radio signal characterized by millisecond duration, extremely high brightness temperature, and large dispersion measure. It remains a mystery in the universe. Advancements in instrumentation have led to the discovery of 816 FRB sources and 7622 bursts from 67 repeating FRBs (https://blinkverse.alkaidos.cn/). This field is undergoing rapid development, rapidly advancing our understanding of the physics of FRBs as new observational data accumulates. The accumulation of data has also promoted exploration of our universe. In this review, we summarize the statistical analysis and cosmological applications using large samples of FRBs, including the energy functions, the waiting time distributions of repeating FRBs, probe of missing baryons and circumgalactic medium in the universe, measurements of cosmological parameters, exploration of the epoch of re-ionization history, and research of the gravitational lensing of FRBs.

A Nançay Radio Telescope study of the hyperactive repeating FRB 20220912A

Abstract The repeating fast radio burst source FRB 20220912A was remarkably active in the weeks after its discovery. Here we report 696 bursts detected with the Nançay Radio Telescope (NRT) as part of the Extragalactic Coherent Light from Astrophysical Transients (ÉCLAT) monitoring campaign. We present 68 observations, conducted from October 2022 to April 2023, with a total duration of 61 hours and an event rate peaking at $75^{+10}_{-9}$ bursts per hour above a fluence threshold of 0.59 Jy ms in the 1.2 − 1.7-GHz band. Most bursts in the sample occur towards the bottom of the observing band. They follow a bimodal wait-time distribution, with peaks at 33.4 ms and 67.0 s. We find a roughly constant dispersion measure (DM) over time (δDM ≲ 2 pc cm−3) when taking into account ‘sad-trombone’ drift, with a mean drift rate of −8.8 MHz ms−1. Nonetheless, we confirm small ∼0.3 pc cm−3 DM variations using microshot structure, while finding that microstructure is rare in our sample – despite the 16 μs time resolution of the data. The cumulative spectral energy distribution shows more high-energy bursts (Eν ≳ 1031 erg Hz−1) than would be expected from a simple power-law distribution. The burst rate per observation appears Poissonian, but the full set of observations is better modelled by a Weibull distribution, showing clustering. We discuss the various observational similarities that FRB 20220912A shares with other (hyper)active repeaters, which as a group are beginning to show a common set of phenomenological traits that provide multiple useful dimensions for their quantitative comparison and modelling.

Contemporaneous X-Ray Observations of 30 Bright Radio Bursts from the Prolific Fast Radio Burst Source FRB 20220912A

We present an extensive contemporaneous X-ray and radio campaign performed on the repeating fast radio burst (FRB) source FRB 20220912A for 8 weeks immediately following the source’s detection by CHIME/FRB. This includes X-ray data from XMM-Newton, NICER, and Swift, and radio detections of FRB 20220912A from CHIME/Pulsar and Effelsberg. We detect no significant X-ray emission at the time of 30 radio bursts with upper limits on a 0.5–10.0 keV X-ray fluence of (1.5–14.5) × 10−10 erg cm−2 (99.7% credible interval, unabsorbed) on a timescale of 100 ms. Translated into a fluence ratio η x/r = F X-ray/F radio, this corresponds to η x/r < 7 × 106. For persistent emission from the location of FRB 20220912A, we derive a 99.7% 0.5–10.0 keV isotropic flux limit of 8.8 × 10−15 erg cm−2 s−1 (unabsorbed) or an isotropic luminosity limit of 1.4 × 1041 erg s−1 at a distance of 362.4 Mpc. We derive a hierarchical extension to the standard Bayesian treatment of low-count and background-contaminated X-ray data, which allows the robust combination of multiple observations. This methodology allows us to place the best (lowest) 99.7% credible interval upper limit on an FRB η x/r to date, η x/r < 2 × 106, assuming that all 30 detected radio bursts are associated with X-ray bursts with the same fluence ratio. If we instead adopt an X-ray spectrum similar to the X-ray burst observed contemporaneously with FRB-like emission from the Galactic magnetar SGR 1935+2154 detected on 2020 April 28, we derive a 99.7% credible interval upper limit on η x/r of 8 × 105, which is only 3 times the observed value of η x/r for SGR 1935+2154.

Morphologies of Bright Complex Fast Radio Bursts with CHIME/FRB Voltage Data

We present the discovery of 12 apparently nonrepeating fast radio burst (FRB) sources, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources, only one of which has been presented previously in the first CHIME/FRB catalog, were selected from a database comprising O(103) CHIME/FRB full-array raw voltage data recordings, based on their large signal-to-noise ratios and complex morphologies. Our study examines the time-frequency characteristics of these bursts, including drifting, microstructure, and periodicities. The events in this sample display a variety of unique drifting phenomenologies that deviate from the linear negative drifting phenomenon seen in many repeating FRBs, and motivate a possible new framework for classifying drifting archetypes. Additionally, we detect microstructure features of duration ≲50 μs in seven events, with some as narrow as ≃7 μs. We find no evidence of significant periodicities between subburst components. Furthermore, we report the polarization characteristics of seven events, including their polarization fractions and Faraday rotation measures (RMs). The observed ∣RM∣ values span a wide range of 17.24(2)–328.06(2) rad m−2, with apparent linear polarization fractions between 0.340(1) and 0.946(3). The morphological properties of the bursts in our sample appear broadly consistent with predictions from both relativistic shock and magnetospheric models of FRB emission, as well as propagation through discrete ionized plasma structures. We address these models and discuss how they can be tested using our improved understanding of morphological archetypes.

On the Dynamical Evolution of the Asteroid Belt in a Massive Star–Neutron Star Binary

Some fast radio bursts (FRBs) exhibit repetitive behaviors, and their origins remain enigmatic. It has been argued that repeating FRBs could be produced by the interaction between a neutron star and an asteroid belt. Here, we consider the systems in which an asteroid belt dwells around a massive star, while a neutron star, as a companion of the massive star, interacts with the belt through gravitational force. Various orbital configurations are assumed for the system. Direct N-body simulations are performed to investigate the dynamical evolution of the asteroids' belt. It is found that a larger orbital eccentricity of the neutron star will destroy the belt more quickly, with a large number of asteroids being scattered out of the system. A low inclination not only suppresses the collisions but also inhibits the ejection rate at early stages. However, highly inclined systems may undergo strong oscillations, resulting in the Kozai–Lidov instabilities. Among the various configurations, a clear periodicity is observed in the collision events for the case with an orbital eccentricity of 0.7 and mutual inclination of 0◦. It is found that such a periodicity can be sustained for at least eight neutron star orbital periods, supporting this mechanism as a possible explanation for periodically repeating FRBs. Our studies also suggest that the active stage of these kinds of FRB sources should be limited, since the asteroid belt would finally be destroyed by the neutron star after multiple passages.

A Radio Study of Persistent Radio Sources in Nearby Dwarf Galaxies: Implications for Fast Radio Bursts

We present 1–12 GHz Karl G. Jansky Very Large Array observations of nine off-nuclear persistent radio sources (PRSs) in nearby (z ≲ 0.055) dwarf galaxies, along with high-resolution European VLBI Network observations for one of them at 1.7 GHz. We explore the plausibility that these PRSs are associated with fast radio burst (FRB) sources by examining their properties—physical sizes, host-normalized offsets, spectral energy distributions (SEDs), radio luminosities, and light curves—and compare them to those of the PRSs associated with FRB 20121102A and FRB 20190520B, two known active galactic nuclei (AGN), and one likely AGN in our sample with comparable data, as well as other radio transients exhibiting characteristics analogous to FRB-PRSs. We identify a single source in our sample, J1136+2643, as the most promising FRB-PRS, based on its compact physical size and host-normalized offset. We further identify two sources, J0019+1507 and J0909+5655, with physical sizes comparable to FRB-PRSs, but which exhibit large offsets and flat spectral indices potentially indicative of a background AGN origin. We test the viability of neutron star wind nebula and hypernebula models for J1136+2643 and find that the physical size, luminosity, and SED of J1136+2643 are broadly consistent with these models. Finally, we discuss the alternative interpretation that the radio sources are instead powered by accreting massive black holes, and we outline future prospects and follow-up observations for differentiating between these scenarios.

Gravitational Self-lensing of Fast Radio Bursts in Neutron Star Magnetospheres. I. The Model

Fast radio bursts (FRBs) are cosmological subsecond bursts of coherent radio emission, whose source is still unknown. To date, the Galactic magnetar SGR 1935 + 2154 is the only astrophysical object known to emit radio bursts akin to FRBs, albeit less powerful, supporting suggestions that FRBs originate from magnetars. Many remarkable properties of FRBs—e.g., the dichotomy between repeaters and one-off sources, and their power-law energy distributions (with typical index ∼2–3)—are not well understood yet. Moreover, the huge radio power released by the most active repeaters is challenging even for the magnetic energy reservoir of magnetars. Here, we assume that FRBs originate from corotating hotspots anchored in neutron star (NS) magnetospheres and occasionally get amplified by large factors via gravitational self-lensing in the strong NS field. We evaluate the probability of amplification and show that: (i) a power-law energy distribution of events ∝E −(2−3) is generally expected; (ii) all FRB sources may be regarded as repeating, their appearance as one-off sources or repeaters being determined by the critical dependence of the amplification probability on the emission geometry and source orientation relative to Earth; and (iii) the most active repeaters, in particular, correspond to extremely rare and finely tuned orientations (∼1 in 106), leading to large probabilities of amplification that make their bursts frequently detectable. At the same time, their power release appears enhanced, typically by factors ≳10, easing their energy budget problem.

Towards solving the origin of circular polarisation in FRB 20180301A

Abstract Fast Radio Bursts (FRBs) are short-timescale transients of extragalactic origin. The number of detected FRBs has grown dramatically since their serendipitous discovery from archival data. Some FRBs have also been seen to repeat. The polarimetric properties of repeating FRBs show diverse behaviour and, at times, extreme polarimetric morphology, suggesting a complex magneto-ionic circumburst environment for this class of FRB. The polarimetric properties such as circular polarisation behaviour of FRBs are crucial for understanding their surrounding magnetic-ionic environment. The circular polarisation previously observed in some of the repeating FRB sources has been attributed to propagation effects such as generalised Faraday rotation (GFR), where conversion from linear to circular polarisation occurs due to the non-circular modes of transmission in relativistic plasma. The discovery burst from the repeating FRB 20180301A showed significant frequency-dependent circular polarisation behaviour, which was initially speculated to be instrumental due to a sidelobe detection. Here we revisit the properties given the subsequent interferometric localisation of the burst, which indicates that the burst was detected in the primary beam of the Parkes/Murriyang 20-cm multibeam receiver. We develop a Bayesian Stokes-Q, U, and V fit method to model the GFR effect, which is independent of the total polarised flux parameter. Using the GFR model we show that the rotation measure (RM) estimated is two orders of magnitude smaller and opposite sign (∼28 rad m−2) than the previously reported value. We interpret the implication of the circular polarisation on its local magnetic environment and reinterpret its long-term temporal evolution in RM.

Time-integrated constraint on neutrino flux of CHIME fast radio burst sources with 10-yr IceCube point-source data

ABSTRACT Despite numerous studies, the sources of IceCube cosmic neutrinos are mostly unidentified. Utilizing recently released IceCube neutrino and CHIME fast radio burst (FRB) catalogues, we examine the possibility of an association between neutrinos and CHIME/FRB catalogue 1 FRBs for both the entire FRB population and individual FRBs using the unbinned maximum likelihood method. Our results do not directly support the possibility of the above-mentioned association with three weighting schemes: equal, total radio fluence, and event rate. We then attempt to constrain the diffuse muon neutrino flux upper limit from CHIME/FRB catalogue 1 FRBs. After considering a completeness correction, we find the 95 per cent diffuse muon neutrino flux upper limit at $100 \,\mathrm{T}\mathrm{eV}$ for all FRB sources in the universe to be ${\sim} 1.01 \times 10^{-18} \,\mathrm{G}^{-1}\mathrm{eV}\mathrm{/}\,\mathrm{c}\mathrm{m}^{2}\,{\rm s}^{-1}\rm {sr}^{-1}$, or ${\sim} 70.3~{{\ \rm per\ cent}}$ of the 10-year diffuse neutrino flux observed by IceCube. Our results match the non-detection results of other studies, but we do not rule out FRBs being a significant contributor to the diffuse neutrino flux measured by IceCube.

Sudden Polarization Angle Jumps of the Repeating Fast Radio Burst FRB 20201124A

We report the first detection of polarization angle orthogonal jumps, a phenomenon previously only observed from radio pulsars, from a fast radio burst (FRB) source FRB 20201124A. We find three cases of orthogonal jumps in over 2000 bursts, all resembling those observed in pulsar single pulses. We propose that the jumps are due to the superposition of two orthogonal emission modes that could only be produced in a highly magnetized plasma, and they are caused by the line of sight sweeping across a rotating magnetosphere. The shortest jump timescale is of the order of 1 millisecond, which hints that the emission modes come from regions smaller than the light cylinder of most pulsars or magnetars. This discovery provides convincing evidence that FRB emission originates from the complex magnetosphere of a magnetar, suggesting an FRB emission mechanism that is analogous to radio pulsars despite a huge luminosity difference between two types of objects.

Coherent Inverse Compton Scattering in Fast Radio Bursts Revisited

Growing observations of temporal, spectral, and polarization properties of fast radio bursts (FRBs) indicate that the radio emission of the majority of bursts is likely produced inside the magnetosphere of its central engine, likely a magnetar. We revisit the idea that FRBs are generated via coherent inverse Compton scattering (ICS) off low-frequency X-mode electromagnetic waves (fast magnetosonic waves) by bunches at a distance of a few hundred times the magnetar radius. The following findings are revealed: (1) Crustal oscillations during a flaring event would excite kHz Alfvén waves. Fast magnetosonic waves with essentially the same frequency can be generated directly or be converted from Alfvén waves at a large radius, with an amplitude large enough to power FRBs via the ICS process. (2) The cross section increases rapidly with radius and significant ICS can occur at r ≳ 100R ⋆ with emission power much greater than the curvature radiation power but still in the linear scattering regime. (3) The low-frequency fast magnetosonic waves naturally redistribute a fluctuating relativistic plasma in the charge-depleted region to form bunches with the right size to power FRBs. (4) The required bunch net charge density can be sub-Goldreich–Julian, which allows a strong parallel electric field to accelerate the charges, maintain the bunches, and continuously power FRB emission. (5) This model can account for a wide range of observed properties of repeating FRB bursts, including high degrees of linear and circular polarization and narrow spectra as observed in many bursts from repeating FRB sources.

A nebular origin for the persistent radio emission of fast radio bursts.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear1. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin2,3. These two FRBs have unusually large Faraday rotation measure values2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source4-8. 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 measureitself7,9. 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.