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  1. Abstract

    The Macquart relation describes the correlation between the dispersion measure (DM) of fast radio bursts (FRBs) and the redshiftzof their host galaxies. The scatter of the Macquart relation is sensitive to the distribution of baryons in the intergalactic medium including those ejected from galactic halos through feedback processes. The variance of the distribution in DMs from the cosmic web (DMcosmic) is parameterized by a fluctuation parameterF. In this work, we present a new measurement ofFusing 78 FRBs of which 21 have been localized to host galaxies. Our analysis simultaneously fits for the Hubble constantH0and the DM distribution due to the FRB host galaxy. We find that the fluctuation parameter is degenerate with these parameters, most notablyH0, and use a uniform prior onH0to measurelog10F>0.86at the 3σconfidence interval and a new constraint on the Hubble constantH0=85.38.1+9.4kms1Mpc1. Using a synthetic sample of 100 localized FRBs, the constraint on the fluctuation parameter is improved by a factor of ∼2. Comparing ourFmeasurement to simulated predictions from cosmological simulation (IllustrisTNG), we find agreement between redshifts 0.4 <z andz< 2.0. However, atz< 0.4, the simulations underpredictF, which we attribute to the rapidly changing extragalactic DM excess distribution at low redshift.

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    Fast radio bursts (FRBs) are transient radio signals of extragalactic origins that are subjected to propagation effects such as dispersion and scattering. It follows then that these signals hold information regarding the medium they have traversed and are hence useful as cosmological probes of the Universe. Recently, FRBs were used to make an independent measure of the Hubble constant H0, promising to resolve the Hubble tension given a sufficient number of detected FRBs. Such cosmological studies are dependent on FRB population statistics, cosmological parameters, and detection biases, and thus it is important to accurately characterize each of these. In this work, we empirically characterize the sensitivity of the Fast Real-time Engine for Dedispersing Amplitudes (FREDDA) which is the current detection system for the Australian Square Kilometre Array Pathfinder (ASKAP). We coherently redisperse high-time resolution data of 13 ASKAP-detected FRBs and inject them into FREDDA to determine the recovered signal-to-noise ratios as a function of dispersion measure. We find that for 11 of the 13 FRBs, these results are consistent with injecting idealized pulses. Approximating this sensitivity function with theoretical predictions results in a systematic error of 0.3 km s−1 Mpc−1 on H0 when it is the only free parameter. Allowing additional parameters to vary could increase this systematic by up to $\sim 1\,$ km s−1 Mpc−1. We estimate that this systematic will not be relevant until ∼400 localized FRBs have been detected, but will likely be significant in resolving the Hubble tension.

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  3. Abstract

    We present a sample of nine fast radio bursts (FRBs) from which we derive magnetic field strengths of the host galaxies represented by normal,z< 0.5 star-forming galaxies with stellar massesM*≈ 108–1010.5M. We find no correlation between the FRB rotation measure (RM) and redshift, which indicates that the RM values are due mostly to the FRB host contribution. This assertion is further supported by a significant positive correlation (Spearman test probabilityPS< 0.05) found between the RM and the estimated host dispersion measure (DMhost; with Spearman rank correlation coefficientrS= +0.75). For these nine galaxies, we estimate their magnetic field strengths projected along the sight line ∣B∣, finding a low median value of 0.5μG. This implies the magnetic fields of our sample of hosts are weaker than those characteristic of the solar neighborhood (≈6μG), but relatively consistent with a lower limit on the observed range of ≈2–10μG for star-forming disk galaxies, especially as we consider reversals in theB-field, and that we are only probing B. We compare to RMs from simulated galaxies of the Auriga project—magneto-hydrodynamic cosmological zoom simulations—and find that the simulations predict the observed values to within a 95% confidence interval. Upcoming FRB surveys will provide hundreds of new FRBs with high-precision localizations, RMs, and imaging follow-up to support further investigation into the magnetic fields of a diverse population ofz< 1 galaxies.

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  4. Abstract

    We present the first X-ray census of fast radio burst (FRB) host galaxies to conduct the deepest search for active galactic nuclei (AGN) and X-ray counterparts to date. Our sample includes seven well-localized FRBs with unambiguous host associations and existing deep Chandra observations, including two events for which we present new observations. We find evidence for AGN in two FRB host galaxies based on the presence of X-ray emission coincident with their centers, including the detection of a luminous (LX≈ 5 × 1042erg s−1) X-ray source at the nucleus of FRB 20190608B’s host, for which we infer an SMBH mass ofMBH∼ 108Mand an Eddington ratioLbol/LEdd≈ 0.02, characteristic of geometrically thin disks in Seyfert galaxies. We also report nebular emission-line fluxes for 24 highly secure FRB hosts (including 10 hosts for the first time), and assess their placement on a BPT diagram, finding that FRB hosts trace the underlying galaxy population. We further find that the hosts of repeating FRBs are not confined to the star-forming locus, contrary to previous findings. Finally, we place constraints on associated X-ray counterparts to FRBs in the context of ultraluminous X-ray sources (ULXs), and find that existing X-ray limits for FRBs rule out ULXs brighter thanLX≳ 1040erg s−1. Leveraging the CHIME/FRB catalog and existing ULX catalogs, we search for spatially coincident ULX–FRB pairs. We identify a total of 28 ULXs spatially coincident with the localization regions for 17 FRBs, but find that the DM-inferred redshifts for the FRBs are inconsistent with the ULX redshifts, disfavoring an association between these specific ULX–FRB pairs.

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  5. Abstract

    We report on the commensal ASKAP detection of a fast radio burst (FRB), FRB 20211127I, and the detection of neutral hydrogen (Hi) emission in the FRB host galaxy, WALLABY J131913–185018 (hereafter W13–18). This collaboration between the CRAFT and WALLABY survey teams marks the fifth, and most distant, FRB host galaxy detected in Hi, not including the Milky Way. We find that W13–18 has an Himass ofMHI= 6.5 × 109M, an Hi-to-stellar mass ratio of 2.17, and coincides with a continuum radio source of flux density at 1.4 GHz of 1.3 mJy. The Higlobal spectrum of W13–18 appears to be asymmetric, albeit the Hiobservation has a low signal-to-noise ratio (S/N), and the galaxy itself appears modestly undisturbed. These properties are compared to the early literature of Hiemission detected in other FRB hosts to date, where either the Higlobal spectra were strongly asymmetric, or there were clearly disrupted Hiintensity map distributions. W13–18 lacks a sufficient S/N to determine whether it is significantly less asymmetric in its Hidistribution than previous examples of FRB host galaxies. However, there are no strong signs of a major interaction in the optical image of the host galaxy that would stimulate a burst of star formation and hence the production of putative FRB progenitors related to massive stars and their compact remnants.

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    We present the first 2.5 yr of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Survey Project. The MPTA aims to precisely measure pulse arrival times from an ensemble of 88 pulsars visible from the Southern hemisphere, with the goal of contributing to the search, detection, and study of nanohertz-frequency gravitational waves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope and operates with a typical observing cadence of 2 weeks using the L-band receiver that records data from 856 to 1712 MHz. We provide a comprehensive description of the observing system, software, and pipelines used and developed for the MeerTime project. The data products made available as part of this data release are from the 78 pulsars that had at least 30 observations between the start of the MeerTime programme in February 2019 and October 2021. These include both sub-banded and band-averaged arrival times and the initial timing ephemerides, noise models, and the frequency-dependent standard templates (portraits) used to derive pulse arrival times. After accounting for detected noise processes in the data, the frequency-averaged residuals of 67 of the pulsars achieved a root-mean-square residual precision of $\lt 1 \, \mu \rm {s}$. We also present a novel recovery of the clock correction waveform solely from pulsar timing residuals and an exploration into preliminary findings of interest to the international pulsar timing community. The arrival times, standards, and full Stokes parameter-calibrated pulsar timing archives are publicly available.

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    We constrain the Hubble constant H0 using Fast Radio Burst (FRB) observations from the Australian Square Kilometre Array Pathfinder (ASKAP) and Murriyang (Parkes) radio telescopes. We use the redshift-dispersion measure (‘Macquart’) relationship, accounting for the intrinsic luminosity function, cosmological gas distribution, population evolution, host galaxy contributions to the dispersion measure (DMhost), and observational biases due to burst duration and telescope beamshape. Using an updated sample of 16 ASKAP FRBs detected by the Commensal Real-time ASKAP Fast Transients (CRAFT) Survey and localized to their host galaxies, and 60 unlocalized FRBs from Parkes and ASKAP, our best-fitting value of H0 is calculated to be $73_{-8}^{+12}$ km s−1 Mpc−1. Uncertainties in FRB energetics and DMhost produce larger uncertainties in the inferred value of H0 compared to previous FRB-based estimates. Using a prior on H0 covering the 67–74 km s−1 Mpc−1 range, we estimate a median ${\rm DM}_{\rm host}= 186_{-48}^{+59}\,{\rm pc \, cm^{-3}}$, exceeding previous estimates. We confirm that the FRB population evolves with redshift similarly to the star-formation rate. We use a Schechter luminosity function to constrain the maximum FRB energy to be log10Emax$=41.26_{-0.22}^{+0.27}$ erg assuming a characteristic FRB emission bandwidth of 1 GHz at 1.3 GHz, and the cumulative luminosity index to be $\gamma =-0.95_{-0.15}^{+0.18}$. We demonstrate with a sample of 100 mock FRBs that H0 can be measured with an uncertainty of ±2.5 km s−1 Mpc−1, demonstrating the potential for clarifying the Hubble tension with an upgraded ASKAP FRB search system. Last, we explore a range of sample and selection biases that affect FRB analyses.

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  8. Context. Fast radio bursts (FRBs) are extremely energetic pulses of millisecond duration and unknown origin. To understand the phenomenon that emits these pulses, targeted and un-targeted searches have been performed for multiwavelength counterparts, including the optical. Aims. The objective of this work is to search for optical transients at the positions of eight well-localized (< 1″) FRBs after the arrival of the burst on different timescales (typically at one day, several months, and one year after FRB detection). We then compare this with known optical light curves to constrain progenitor models. Methods. We used the Las Cumbres Observatory Global Telescope (LCOGT) network to promptly take images with its network of 23 telescopes working around the world. We used a template subtraction technique to analyze all the images collected at differing epochs. We have divided the difference images into two groups: In one group we use the image of the last epoch as a template, and in the other group we use the image of the first epoch as a template. We then searched for optical transients at the localizations of the FRBs in the template subtracted images. Results. We have found no optical transients and have therefore set limiting magnitudes to the optical counterparts. Typical limits in apparent and absolute magnitudes for our LCOGT data are ∼22 and −19 mag in the r band, respectively. We have compared our limiting magnitudes with light curves of super-luminous supernovae (SLSNe), Type Ia supernovae (SNe Ia), supernovae associated with gamma-ray bursts (GRB-SNe), a kilonova, and tidal disruption events (TDEs). Conclusions. Assuming that the FRB emission coincides with the time of explosion of these transients, we rule out associations with SLSNe (at the ∼99.9% confidence level) and the brightest subtypes of SNe Ia, GRB-SNe, and TDEs (at a similar confidence level). However, we cannot exclude scenarios where FRBs are directly associated with the faintest of these subtypes or with kilonovae. 
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  9. ABSTRACT We report the results of the rapid follow-up observations of gamma-ray bursts (GRBs) detected by the Fermi satellite to search for associated fast radio bursts. The observations were conducted with the Australian Square Kilometre Array Pathfinder at frequencies from 1.2 to 1.4 GHz. A set of 20 bursts, of which four were short GRBs, were followed up with a typical latency of about 1 min, for a duration of up to 11 h after the burst. The data were searched using 4096 dispersion measure trials up to a maximum dispersion measure of 3763 pc cm−3, and for pulse widths w over a range of duration from 1.256 to 40.48 ms. No associated pulsed radio emission was observed above $26 \, {\rm Jy\, ms}\, (w/1\, {\rm ms})^{-1/2}$ for any of the 20 GRBs. 
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