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Abstract We report the discovery of CHIME J1634+44, a long-period radio transient (LPT) unique for two aspects: it is the first known LPT to emit fully circularly polarized radio bursts, and it is the first LPT with a significant spin-up. Given that high circular polarization (>90%) has been observed in FRB 20201124A and in some giant pulses of PSR B1937+21, we discuss the implications of the high circular polarization of CHIME J1634+44 and conclude its emission mechanism is likely to be “pulsar-like.” While CHIME J1634+44 has a pulse period of 841 s, its burst arrival patterns are indicative of a secondary 4206 s period, probably associated with binary activity. The timing properties suggest it has a significantly negative period derivative of $\dot{P}=-9.03\left(0.11\right)\times {10}^{-12}$s s⁻¹. Few systems have been known to spin up, most notably transitional millisecond pulsars and cataclysmic binaries, both of which seem unlikely progenitors for CHIME J1634+44. If the period was only associated with the spin of the object, then the spin-up is likely generated by accretion of material from a companion. If, however, the radio pulse period and the orbital period are locked, as appears to be the case for two other LPTs, the spin-up of CHIME J1634+44 could be driven by gravitational-wave radiation. 

The Owens Valley Radio Observatory Long Wavelength Array is a low radio frequency all-sky imaging radio interferometer. The full 352-element array will generate more than 2 TB of visibility data per hour of observation. One of the array’s primary science cases, the search for variable radio emission from exoplanets and for transients, require fast and high dynamic range interferometric imaging. Here we detail the design and implementation of a two-pipeline infrastructure that minimizes development cost: an offline pipeline that facilitates experimentation with existing pack-ages, and a real-time pipeline that minimizes overhead. 

Abstract We report on a full-polarization analysis of the first 25 as yet nonrepeating fast radio bursts (FRBs) detected at 1.4 GHz by the 110-antenna Deep Synoptic Array (DSA-110) during commissioning observations. We present details of the data-reduction, calibration, and analysis procedures developed for this novel instrument. Faraday rotation measures (RMs) are searched between ±10⁶rad m⁻²and detected for 20 FRBs, with magnitudes ranging from 4 to 4670 rad m⁻². Fifteen out of 25 FRBs are consistent with 100% polarization, 10 of which have high (≥70%) linear-polarization fractions and two of which have high (≥30%) circular-polarization fractions. Our results disfavor multipath RM scattering as a dominant depolarization mechanism. Polarization-state and possible RM variations are observed in the four FRBs with multiple subcomponents. We combine the DSA-110 sample with polarimetry of previously published FRBs, and compare the polarization properties of FRB subpopulations and FRBs with Galactic pulsars. Although FRB polarization fractions are typically higher than those of Galactic pulsars, and cover a wider range than those of pulsar single pulses, they resemble those of the youngest (characteristic ages <10⁵yr) pulsars. Our results support a scenario wherein FRB emission is intrinsically highly linearly polarized, and propagation effects can result in conversion to circular polarization and depolarization. Young pulsar emission and magnetospheric propagation geometries may form a useful analogy for the origin of FRB polarization. 

Abstract The first fast radio burst (FRB) to be precisely localized was associated with a luminous persistent radio source (PRS). Recently, a second FRB/PRS association was discovered for another repeating source of FRBs. However, it is not clear what makes FRBs or PRS or how they are related. We compile FRB and PRS properties to consider the population of FRB/PRS sources. We suggest a practical definition for PRS as FRB associations with luminosity greater than 10²⁹erg s⁻¹Hz⁻¹that are not attributed to star formation activity in the host galaxy. We model the probability distribution of the fraction of FRBs with PRS for repeaters and nonrepeaters, showing there is not yet evidence for repeaters to be preferentially associated with PRS. We discuss how FRB/PRS sources may be distinguished by the combination of active repetition and an excess dispersion measure local to the FRB environment. We use CHIME/FRB event statistics to bound the mean per-source repetition rate of FRBs to be between 25 and 440 yr⁻¹. We use this to provide a bound on the density of FRB-emitting sources in the local universe of between 2.2 × 10²and 5.2 × 10⁴Gpc⁻³assuming a pulsar-like beamwidth for FRB emission. This density implies that PRS may comprise as much as 1% of compact, luminous radio sources detected in the local universe. The cosmic density and phenomenology of PRS are similar to that of the newly discovered, off-nuclear “wandering” active galactic nuclei (AGN). We argue that it is likely that some PRS have already been detected and misidentified as AGN. 

ABSTRACT Fast radio bursts (FRBs) are millisecond-time-scale radio transients, the origins of which are predominantly extragalactic and likely involve highly magnetized compact objects. FRBs undergo multipath propagation, or scattering, from electron density fluctuations on sub-parsec scales in ionized gas along the line of sight. Scattering observations have located plasma structures within FRB host galaxies, probed Galactic and extragalactic turbulence, and constrained FRB redshifts. Scattering also inhibits FRB detection and biases the observed FRB population. We report the detection of scattering times from the repeating FRB 20190520B that vary by up to a factor of 2 or more on minutes to days-long time-scales. In one notable case, the scattering time varied from 7.9 ± 0.4 ms to less than 3.1 ms ($$95{{\ \rm per\ cent}}$$ confidence) over 2.9 min at 1.45 GHz. The scattering times appear to be uncorrelated between bursts or with dispersion and rotation measure variations. Scattering variations are attributable to dynamic, inhomogeneous plasma in the circumsource medium, and analogous variations have been observed from the Crab pulsar. Under such circumstances, the frequency dependence of scattering can deviate from the typical power law used to measure scattering. Similar variations may therefore be detectable from other FRBs, even those with inconspicuous scattering, providing a unique probe of small-scale processes within FRB environments. 

Abstract The stellar population environments that are associated with fast radio burst (FRB) sources provide important insights for developing their progenitor theories. We expand the diversity of known FRB host environments by reporting two FRBs in massive galaxy clusters that were discovered by the Deep Synoptic Array (DSA-110) during its commissioning observations. FRB 20220914A has been localized to a star-forming, late-type galaxy at a redshift of 0.1139 with multiple starbursts at lookback times less than ∼3.5 Gyr in the A2310 galaxy cluster. Although the host galaxy of FRB 20220914A is similar to typical FRB hosts, the FRB 20220509G host stands out as a quiescent, early-type galaxy at a redshift of 0.0894 in the A2311 galaxy cluster. The discovery of FRBs in both late- and early-type galaxies adds to the body of evidence that the FRB sources have multiple formation channels. Therefore, even though FRB hosts are typically star-forming, there must exist formation channels that are consistent with old stellar population in galaxies. The varied star formation histories of the two FRB hosts that we report here indicate a wide delay-time distribution of FRB progenitors. Future work in constraining the FRB delay-time distribution, using the methods that we develop herein, will prove crucial in determining the evolutionary histories of FRB sources. 

Abstract The hot gas that constitutes the intracluster medium (ICM) has been studied at X-ray and millimeter/submillimeter wavelengths (Sunyaev–Zel’dovich effect) for decades. Fast radio bursts (FRBs) offer an additional method of directly measuring the ICM and gas surrounding clusters via observables such as dispersion measure (DM) and Faraday rotation measure. We report the discovery of two FRB sources detected with the Deep Synoptic Array whose host galaxies belong to massive galaxy clusters. In both cases, the FRBs exhibit excess extragalactic DM, some of which likely originate in the ICM of their respective clusters. FRB 20220914A resides in the galaxy cluster A2310 at z = 0.1125 with a projected offset from the cluster center of 520 ± 50 kpc. The host of a second source, FRB 20220509G, is an elliptical galaxy at z = 0.0894 that belongs to the galaxy cluster A2311 at the projected offset of 870 ± 50 kpc. These sources represent the first time an FRB has been localized to a galaxy cluster. We combine our FRB data with archival X-ray, Sunyaev–Zel'dovich (SZ), and optical observations of these clusters in order to infer properties of the ICM, including a measurement of gas temperature from DM and y SZ of 0.8–3.9 keV. We then compare our results to massive cluster halos from the IllustrisTNG simulation. Finally, we describe how large samples of localized FRBs from future surveys will constrain the ICM, particularly beyond the virial radius of clusters. 

Abstract Faraday rotation measures (RMs) of fast radio bursts (FRBs) offer the prospect of directly measuring extragalactic magnetic fields. We present an analysis of the RMs of 10 as yet nonrepeating FRBs detected and localized to host galaxies with robust redshift measurements by the 63-antenna prototype of the Deep Synoptic Array (DSA-110). We combine this sample with published RMs of 15 localized FRBs, nine of which are repeating sources. For each FRB in the combined sample, we estimate the host-galaxy dispersion measure (DM) contributions and extragalactic RM. We find compelling evidence that the extragalactic components of FRB RMs are often dominated by contributions from the host-galaxy interstellar medium (ISM). Specifically, we find that both repeating and as yet nonrepeating FRBs show a correlation between the host DM and host RM in the rest frame, and we find an anticorrelation between extragalactic RM (in the observer frame) and redshift for nonrepeaters, as expected if the magnetized plasma is in the host galaxy. Important exceptions to the ISM origin include a dense, magnetized circumburst medium in some repeating FRBs, and the intracluster medium of host or intervening galaxy clusters. We find that the estimated ISM magnetic-field strengths, ${\overline{B}}_{\mid \mid }$, are characteristically ∼1–2μG larger than those inferred from Galactic radio pulsars. This suggests either increased ISM magnetization in FRB hosts in comparison with the Milky Way, or that FRBs preferentially reside in regions of increased magnetic-field strength within their hosts. 

ABSTRACT Fast-rotating pulsars and magnetars have been suggested as the central engines of superluminous supernovae (SLSNe) and fast radio bursts, and this scenario naturally predicts non-thermal synchrotron emission from their nascent pulsar wind nebulae (PWNe). We report results of high-frequency radio observations with ALMA and NOEMA for three SLSNe (SN 2015bn, SN 2016ard, and SN 2017egm), and present a detailed theoretical model to calculate non-thermal emission from PWNe with an age of ∼1−3 yr. We find that the ALMA data disfavours a PWN model motivated by the Crab nebula for SN 2015bn and SN 2017egm, and argue that this tension can be resolved if the nebular magnetization is very high or very low. Such models can be tested by future MeV–GeV gamma-ray telescopes such as AMEGO.