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We present the discovery of a 100 kpc low-frequency radio tail behind the nearby group galaxy, NGC 2276. The extent of this tail is a factor of ten larger than previously reported from higher-frequency radio and X-ray imaging. The radio morphology of the galaxy disc and tail suggest that the tail was produced via ram-pressure stripping, cementing NGC 2276 as the clearest known example of ram-pressure stripping in a low-mass group. With multi-frequency imaging, we extract radio continuum spectra between ∼50 MHz and 1.2 GHz as a function of projected distance along the tail. All of the spectra are well fit by a simple model of spectral ageing due to synchrotron and inverse-Compton losses. From these fits we estimate a velocity of 870 km s^‑1 for the stripped plasma across the plane of the sky, and a three-dimensional orbital velocity of 970 km s^‑1 for NGC 2276. The orbital speed that we derive is in excellent agreement with the previous estimates from an X-ray shock analysis, despite the completely independent methodology.

We present the discovery of a 100 kpc low-frequency radio tail behind the nearby group galaxy, NGC 2276. The extent of this tail is a factor of ten larger than previously reported from higher-frequency radio and X-ray imaging. The radio morphology of the galaxy disc and tail suggest that the tail was produced via ram-pressure stripping, cementing NGC 2276 as the clearest known example of ram-pressure stripping in a low-mass group. With multi-frequency imaging, we extract radio continuum spectra between ∼50 MHz and 1.2 GHz as a function of projected distance along the tail. All of the spectra are well fit by a simple model of spectral ageing due to synchrotron and inverse-Compton losses. From these fits we estimate a velocity of 870 km s^‑1 for the stripped plasma across the plane of the sky, and a three-dimensional orbital velocity of 970 km s^‑1 for NGC 2276. The orbital speed that we derive is in excellent agreement with the previous estimates from an X-ray shock analysis, despite the completely independent methodology.

Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different time-scales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time. Applications of FR filtering include separating effects that are correlated with the rotating sky versus those relative to the ground, down-weighting emission in the primary beam sidelobes, and suppressing noise. FR filtering causes the noise contributions to the visibility data to become correlated in time, however, making interpretation of subsequent averaging and error estimation steps more subtle. In this paper, we describe fringe-rate filters that are implemented using discrete prolate spheroidal sequences, and designed for two different purposes-beam sidelobe/horizon suppression (the 'mainlobe' filter), and ground-locked systematics removal (the 'notch' filter). We apply these to simulated data, and study how their properties affect visibilities and power spectra generated from the simulations. Included is an introduction to fringe-rate filtering and a demonstration of fringe-rate filters applied to simple situations to aid understanding.

The gas surrounding first-generation (Population III, hereafter Pop III) stars is expected to emit a distinct signature in the form of the He II recombination line at 1640 Å(He II λ1640). Here we explore the challenges and opportunities in identifying this elusive stellar population via the He II λ1640 in M _⋆ > 10^7.5 M _⊙ galaxies during the Epoch of Reionization (z ≃ 6–10), using JWST/NIRSpec. With this aim in mind, we combine cosmological dustyGadget simulations with analytical modeling of the intrinsic He II emission. While tentative candidates with bright He II emission like GN-z11 have been proposed in the literature, the prevalence of such bright systems remains unclear due to significant uncertainties involved in the prediction of the He II luminosity. In fact, similar Pop III clumps might be almost 2 orders of magnitude fainter, primarily depending on the assumed Pop III formation efficiency and initial mass function in star-forming clouds, while the effect of stellar mass loss is responsible for a factor of order unity. Moreover, up to ∼90% of these clumps might be missed with NIRSpec multi-object spectroscopy due to the limited field of view, while this problem appears to be less severe with NIRSpec's integral field unit. We investigate the potential of deep spectroscopy targeting peripheral Pop III clumps around bright, massive galaxies to achieve a clear detection of the first stars.

Giant exoplanets orbiting close to their host stars are unlikely to have formed in their present configurations¹. These `hot Jupiter' planets are instead thought to have migrated inward from beyond the ice line and several viable migration channels have been proposed, including eccentricity excitation through angular-momentum exchange with a third body followed by tidally driven orbital circularization^2,3. The discovery of the extremely eccentric (e = 0.93) giant exoplanet HD 80606 b (ref. ⁴) provided observational evidence that hot Jupiters may have formed through this high-eccentricity tidal-migration pathway⁵. However, no similar hot-Jupiter progenitors have been found and simulations predict that one factor affecting the efficacy of this mechanism is exoplanet mass, as low-mass planets are more likely to be tidally disrupted during periastron passage^6-8. Here we present spectroscopic and photometric observations of TIC 241249530 b, a high-mass, transiting warm Jupiter with an extreme orbital eccentricity of e = 0.94. The orbit of TIC 241249530 b is consistent with a history of eccentricity oscillations and a future tidal circularization trajectory. Our analysis of the mass and eccentricity distributions of the transiting-warm-Jupiter population further reveals a correlation between high mass and high eccentricity.

Aims: The multifaceted central radio galaxy of the cluster RBS 797 shows several episodes of jet activity in multiple directions. We wish to understand the causes behind these dramatic misalignments and measure the timescales of the successive outbursts.
Methods: We present a multifrequency (144 MHz - 9 GHz) and multiscale (5 pc - 50 kpc) investigation of the central radio galaxy in RBS 797, by means of JVLA, LOFAR (with international stations), e-Merlin, VLBA, and EVN data. We investigate the morphological and spectral properties of the radio lobes, the jets, and the active core.
Results: We confirm the co-spatiality of the radio lobes with the four perpendicular X-ray cavities previously discovered. The radiative ages of the east-west lobes (31.4 ± 6.6 Myr) and of the north-south lobes (32.1 ± 9.9 Myr) support a coeval origin of the perpendicular outbursts, which also have similar active phase duration (∼12 Myr). Based on the analysis of the inner north-south jets (on scales of ≤10 kpc), we (a) confirm the S-shaped jet morphology; (b) show the presence of two hotspots per jet with a similar spectral index; and (c) estimate the age of the twisting north-south jets to be less than ∼8 Myr. Based on these results, we determine that jet precession, with a period ∼9 Myr, half-opening angle ∼24°, and jet advance speed ∼0.01c, can explain the properties of the north-south jets. We also find that the synchrotron injection index has steepened from the large, older outbursts (Γ ∼ 0.5) to the younger S-shaped jets (Γ ∼ 0.9), possibly due to a transition from FR I-like to FR II-like activity. The e-Merlin, VLBA, and EVN data reveal a single, compact core at the heart of RBS 797, surrounded by extended radio emission whose orientation depends on the spatial scale sampled by the data.
Conclusions: We explore several engine-based scenarios to explain these results. Piecing together the available evidence, we argue that RBS 797 likely hosts (or hosted) binary active supermassive black holes (SMBHs). The detection of a single component in the VLBA and EVN data is still consistent with this interpretation, since the predicted separation of the binary SMBHs (≤0.6 pc) is an order of magnitude smaller than the resolution of the available radio data (5 pc).

Aims: The multifaceted central radio galaxy of the cluster RBS 797 shows several episodes of jet activity in multiple directions. We wish to understand the causes behind these dramatic misalignments and measure the timescales of the successive outbursts.
Methods: We present a multifrequency (144 MHz - 9 GHz) and multiscale (5 pc - 50 kpc) investigation of the central radio galaxy in RBS 797, by means of JVLA, LOFAR (with international stations), e-Merlin, VLBA, and EVN data. We investigate the morphological and spectral properties of the radio lobes, the jets, and the active core.
Results: We confirm the co-spatiality of the radio lobes with the four perpendicular X-ray cavities previously discovered. The radiative ages of the east-west lobes (31.4 ± 6.6 Myr) and of the north-south lobes (32.1 ± 9.9 Myr) support a coeval origin of the perpendicular outbursts, which also have similar active phase duration (∼12 Myr). Based on the analysis of the inner north-south jets (on scales of ≤10 kpc), we (a) confirm the S-shaped jet morphology; (b) show the presence of two hotspots per jet with a similar spectral index; and (c) estimate the age of the twisting north-south jets to be less than ∼8 Myr. Based on these results, we determine that jet precession, with a period ∼9 Myr, half-opening angle ∼24°, and jet advance speed ∼0.01c, can explain the properties of the north-south jets. We also find that the synchrotron injection index has steepened from the large, older outbursts (Γ ∼ 0.5) to the younger S-shaped jets (Γ ∼ 0.9), possibly due to a transition from FR I-like to FR II-like activity. The e-Merlin, VLBA, and EVN data reveal a single, compact core at the heart of RBS 797, surrounded by extended radio emission whose orientation depends on the spatial scale sampled by the data.
Conclusions: We explore several engine-based scenarios to explain these results. Piecing together the available evidence, we argue that RBS 797 likely hosts (or hosted) binary active supermassive black holes (SMBHs). The detection of a single component in the VLBA and EVN data is still consistent with this interpretation, since the predicted separation of the binary SMBHs (≤0.6 pc) is an order of magnitude smaller than the resolution of the available radio data (5 pc).

Aims: The multifaceted central radio galaxy of the cluster RBS 797 shows several episodes of jet activity in multiple directions. We wish to understand the causes behind these dramatic misalignments and measure the timescales of the successive outbursts.
Methods: We present a multifrequency (144 MHz - 9 GHz) and multiscale (5 pc - 50 kpc) investigation of the central radio galaxy in RBS 797, by means of JVLA, LOFAR (with international stations), e-Merlin, VLBA, and EVN data. We investigate the morphological and spectral properties of the radio lobes, the jets, and the active core.
Results: We confirm the co-spatiality of the radio lobes with the four perpendicular X-ray cavities previously discovered. The radiative ages of the east-west lobes (31.4 ± 6.6 Myr) and of the north-south lobes (32.1 ± 9.9 Myr) support a coeval origin of the perpendicular outbursts, which also have similar active phase duration (∼12 Myr). Based on the analysis of the inner north-south jets (on scales of ≤10 kpc), we (a) confirm the S-shaped jet morphology; (b) show the presence of two hotspots per jet with a similar spectral index; and (c) estimate the age of the twisting north-south jets to be less than ∼8 Myr. Based on these results, we determine that jet precession, with a period ∼9 Myr, half-opening angle ∼24°, and jet advance speed ∼0.01c, can explain the properties of the north-south jets. We also find that the synchrotron injection index has steepened from the large, older outbursts (Γ ∼ 0.5) to the younger S-shaped jets (Γ ∼ 0.9), possibly due to a transition from FR I-like to FR II-like activity. The e-Merlin, VLBA, and EVN data reveal a single, compact core at the heart of RBS 797, surrounded by extended radio emission whose orientation depends on the spatial scale sampled by the data.
Conclusions: We explore several engine-based scenarios to explain these results. Piecing together the available evidence, we argue that RBS 797 likely hosts (or hosted) binary active supermassive black holes (SMBHs). The detection of a single component in the VLBA and EVN data is still consistent with this interpretation, since the predicted separation of the binary SMBHs (≤0.6 pc) is an order of magnitude smaller than the resolution of the available radio data (5 pc).

Aims: The multifaceted central radio galaxy of the cluster RBS 797 shows several episodes of jet activity in multiple directions. We wish to understand the causes behind these dramatic misalignments and measure the timescales of the successive outbursts.
Methods: We present a multifrequency (144 MHz - 9 GHz) and multiscale (5 pc - 50 kpc) investigation of the central radio galaxy in RBS 797, by means of JVLA, LOFAR (with international stations), e-Merlin, VLBA, and EVN data. We investigate the morphological and spectral properties of the radio lobes, the jets, and the active core.
Results: We confirm the co-spatiality of the radio lobes with the four perpendicular X-ray cavities previously discovered. The radiative ages of the east-west lobes (31.4 ± 6.6 Myr) and of the north-south lobes (32.1 ± 9.9 Myr) support a coeval origin of the perpendicular outbursts, which also have similar active phase duration (∼12 Myr). Based on the analysis of the inner north-south jets (on scales of ≤10 kpc), we (a) confirm the S-shaped jet morphology; (b) show the presence of two hotspots per jet with a similar spectral index; and (c) estimate the age of the twisting north-south jets to be less than ∼8 Myr. Based on these results, we determine that jet precession, with a period ∼9 Myr, half-opening angle ∼24°, and jet advance speed ∼0.01c, can explain the properties of the north-south jets. We also find that the synchrotron injection index has steepened from the large, older outbursts (Γ ∼ 0.5) to the younger S-shaped jets (Γ ∼ 0.9), possibly due to a transition from FR I-like to FR II-like activity. The e-Merlin, VLBA, and EVN data reveal a single, compact core at the heart of RBS 797, surrounded by extended radio emission whose orientation depends on the spatial scale sampled by the data.
Conclusions: We explore several engine-based scenarios to explain these results. Piecing together the available evidence, we argue that RBS 797 likely hosts (or hosted) binary active supermassive black holes (SMBHs). The detection of a single component in the VLBA and EVN data is still consistent with this interpretation, since the predicted separation of the binary SMBHs (≤0.6 pc) is an order of magnitude smaller than the resolution of the available radio data (5 pc).

Context. Ice-coated dust grains provide the main reservoir of volatiles that play an important role in planet formation processes and may become incorporated into planetary atmospheres. However, due to observational challenges, the ice abundance distribution in protoplanetary disks is not well constrained. With the advent of the James Webb Space Telescope (JWST), we are in a unique position to observe these ices in the near- to mid-infrared and constrain their properties in Class II protoplanetary disks. Aims. We present JWST Mid-InfraRed Imager (MIRI) observations of the edge-on disk HH 48 NE carried out as part of the Direc- tor's Discretionary Early Release Science program Ice Age, completing the ice inventory of HH 48 NE by combining the MIRI data (5–28 μm) with those of NIRSpec (2.7–5 μm). Methods. We used radiative transfer models tailored to the system, including silicates, ices, and polycyclic aromatic hydrocarbons (PAHs) to reproduce the observed spectrum of HH 48 NE with a parameterized model. The model was then used to identify ice species and constrain spatial information about the ices in the disk. Results. The mid-infrared spectrum of HH 48 NE is relatively flat, with weak ice absorption features. We detect CO₂, NH₃, H₂O, and tentatively CH₄ and NH₄⁺. Radiative transfer models suggest that ice absorption features are produced predominantly in the 50–100 au region of the disk. The CO₂ feature at 15 μm probes a region closer to the midplane (z/r = 0.1–0.15) than the corresponding feature at 4.3 μm (z/r = 0.2–0.6), but all observations trace regions significantly above the midplane reservoirs where we expect the bulk of the ice mass to be located. Ices must reach a high scale height (z/r ~ 0.6; corresponding to a modeled dust extinction A_v ~ 0.1), in order to be consistent with the observed vertical distribution of the peak ice optical depths. The weakness of the CO₂ feature at 15 μm relative to the 4.3 μm feature and the red emission wing of the 4.3 μm CO₂ feature are both consistent with ices being located at a high elevation in the disk. The retrieved NH₃ abundance and the upper limit on the CH₃OH abundance relative to H₂O are significantly lower than those in the interstellar medium, but consistent with cometary observations. The contrast of the PAH emission features with the continuum is stronger than for similar face-on protoplanetary disks, which is likely a result of the edge-on system geometry. Modeling based on the relative strength of the emission features suggests that the PAH emission originates in the disk surface layer rather than the ice absorbing layer. Conclusions. Full wavelength coverage is required to properly study the abundance distribution of ices in disks. To explain the pres- ence of ices at high disk altitudes, we propose two possible scenarios: a disk wind that entrains sufficient amounts of dust, and thus blocks part of the stellar UV radiation, or vertical mixing that cycles enough ices into the upper disk layers to balance ice photodesorption from the grains.

Context. Ice-coated dust grains provide the main reservoir of volatiles that play an important role in planet formation processes and may become incorporated into planetary atmospheres. However, due to observational challenges, the ice abundance distribution in protoplanetary disks is not well constrained. With the advent of the James Webb Space Telescope (JWST), we are in a unique position to observe these ices in the near- to mid-infrared and constrain their properties in Class II protoplanetary disks. Aims. We present JWST Mid-InfraRed Imager (MIRI) observations of the edge-on disk HH 48 NE carried out as part of the Direc- tor's Discretionary Early Release Science program Ice Age, completing the ice inventory of HH 48 NE by combining the MIRI data (5–28 μm) with those of NIRSpec (2.7–5 μm). Methods. We used radiative transfer models tailored to the system, including silicates, ices, and polycyclic aromatic hydrocarbons (PAHs) to reproduce the observed spectrum of HH 48 NE with a parameterized model. The model was then used to identify ice species and constrain spatial information about the ices in the disk. Results. The mid-infrared spectrum of HH 48 NE is relatively flat, with weak ice absorption features. We detect CO₂, NH₃, H₂O, and tentatively CH₄ and NH₄⁺. Radiative transfer models suggest that ice absorption features are produced predominantly in the 50–100 au region of the disk. The CO₂ feature at 15 μm probes a region closer to the midplane (z/r = 0.1–0.15) than the corresponding feature at 4.3 μm (z/r = 0.2–0.6), but all observations trace regions significantly above the midplane reservoirs where we expect the bulk of the ice mass to be located. Ices must reach a high scale height (z/r ~ 0.6; corresponding to a modeled dust extinction A_v ~ 0.1), in order to be consistent with the observed vertical distribution of the peak ice optical depths. The weakness of the CO₂ feature at 15 μm relative to the 4.3 μm feature and the red emission wing of the 4.3 μm CO₂ feature are both consistent with ices being located at a high elevation in the disk. The retrieved NH₃ abundance and the upper limit on the CH₃OH abundance relative to H₂O are significantly lower than those in the interstellar medium, but consistent with cometary observations. The contrast of the PAH emission features with the continuum is stronger than for similar face-on protoplanetary disks, which is likely a result of the edge-on system geometry. Modeling based on the relative strength of the emission features suggests that the PAH emission originates in the disk surface layer rather than the ice absorbing layer. Conclusions. Full wavelength coverage is required to properly study the abundance distribution of ices in disks. To explain the pres- ence of ices at high disk altitudes, we propose two possible scenarios: a disk wind that entrains sufficient amounts of dust, and thus blocks part of the stellar UV radiation, or vertical mixing that cycles enough ices into the upper disk layers to balance ice photodesorption from the grains.

The classical T Tauri star (CTTS) stage is a critical phase of the star and planet formation process. In an effort to better understand the mass accretion processes, which can dictate future stellar evolution and planet formation, a multiepoch, multiwavelength photometric and spectroscopic monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was carried out in 2021 and 2022/2023 as part of the Outflows and Disks around Young Stars: Synergies for the Exploration of ULLYSES Spectra program. Here we focus on the Hubble Space Telescope (HST) UV spectra obtained by the HST Director's Discretionary Time UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program. Using accretion shock modeling, we find that all targets exhibit accretion variability, varying from short increases in accretion rate by up to a factor of 3 within 48 hr to longer decreases in accretion rate by a factor of 2.5 over the course of 1 yr. This is despite the generally consistent accretion morphology within each target. Additionally, we test empirical relationships between accretion rate and UV luminosity and find stark differences, showing that these relationships should not be used to estimate the accretion rate for an individual target. Our work reinforces that future multiepoch and simultaneous multiwavelength studies are critical in our understanding of the accretion process in low-mass star formation.

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R _⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. ^* Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R _⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. ^* Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

Classical T Tauri Stars (CTTSs) are highly variable stars that possess gas- and dust-rich disks from which planets form. Much of their variability is driven by mass accretion from the surrounding disk, a process that is still not entirely understood. A multiepoch optical spectral monitoring campaign of four CTTSs (TW Hya, RU Lup, BP Tau, and GM Aur) was conducted along with contemporaneous Hubble Space Telescope (HST) UV spectra and ground-based photometry in an effort to determine accretion characteristics and gauge variability in this sample. Using an accretion flow model, we find that the magnetospheric truncation radius varies between 2.5 and 5 R _⋆ across all of our observations. There is also significant variability in all emission lines studied, particularly Hα, Hβ, and Hγ. Using previously established relationships between line luminosity and accretion, we find that, on average, most lines reproduce accretion rates consistent with accretion shock modeling of HST spectra to within 0.5 dex. Looking at individual contemporaneous observations, however, these relationships are less accurate, suggesting that variability trends differ from the trends of the population and that these empirical relationships should be used with caution in studies of variability. ^* Based on observations collected at the European Southern Observatory under ESO program 106.20Z8.

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 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.

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 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.

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 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.

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 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.

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 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.