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  1. Abstract

    A sample of 14 FRBs with measured redshifts and scattering times is used to assess contributions to dispersion and scattering from the intergalactic medium (IGM), galaxy halos, and the disks of host galaxies. The IGM and galaxy halos contribute significantly to dispersion measures (DMs) but evidently not to scattering, which is then dominated by host galaxies. This enables the usage of scattering times for estimating DM contributions from host galaxies and also for a combined scattering–dispersion redshift estimator. Redshift estimation is calibrated using the scattering of Galactic pulsars after taking into account different scattering geometries for Galactic and intergalactic lines of sight. The DM-only estimator has a bias of ∼0.1 and rms error of ∼0.15 in the redshift estimate for an assumed ad hoc value of 50 pc cm−3for the host galaxy’s DM contribution. The combined redshift estimator shows less bias by a factor of 4 to 10 and a 20%–40% smaller rms error. We find that values for the baryonic fraction of the ionized IGMfigm≃ 0.85 ± 0.05 optimize redshift estimation using dispersion and scattering. Our study suggests that 2 of the 14 candidate galaxy associations (FRB 20190523A and FRB 20190611B) should be reconsidered.

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  2. Abstract

    We analyze the slow periodicities identified in burst sequences from FRB 121102 and FRB 180916 with periods of about 16 and 160 days, respectively, while also addressing the absence of any fast periodicity that might be associated with the spin of an underlying compact object. Both phenomena can be accounted for by a young, highly magnetized, precessing neutron star that emits beamed radiation with significant imposed phase jitter. Sporadic narrow-beam emission into an overall wide solid angle can account for the necessary phase jitter, but the slow periodicities with 25%–55% duty cycles constrain beam traversals to be significantly smaller. Instead, phase jitter may result from variable emission altitudes that yield large retardation and aberration delays. A detailed arrival time analysis for triaxial precession includes wobble of the radio beam and the likely larger, cyclical torque resulting from the changes in the spin–magnetic moment angle. These effects will confound identification of the fast periodicity in sparse data sets longer than about a quarter of a precession cycle unless fitted for and removed as with orbital fitting. Stochastic spin noise, likely to be much larger than in radio pulsars, may hinder detection of any fast periodicity in data spans longer than a few days. These decoherence effects will dissipate as sources of fast radio bursts age, so they may evolve into objects with properties similar to Galactic magnetars.

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  3. Abstract

    The repeating fast radio bursts (FRBs) 180916.J0158 and 121102 are visible during periodically occurring windows in time. We consider the constraints on internal magnetic fields and geometries if the cyclical behavior observed for FRB 180916.J0158 and FRB 121102 is due to the precession of magnetars. In order to frustrate vortex line pinning we argue that internal magnetic fields must be stronger than about 1016G, which is large enough to prevent superconductivity in the core and destroy the crustal lattice structure. We conjecture that the magnetic field inside precessing magnetars has three components: (1) a dipole component with characteristic strength ∼ 1014G; (2) a toroidal component with characteristic strength ∼ 1015–1016G that only occupies a modest fraction of the stellar volume; and (3) a disordered field with characteristic strength ∼ 1016G. The disordered field is primarily responsible for permitting precession, which stops once this field component decays away, which we conjecture happens after ∼1000 yr. Conceivably, as the disordered component damps bursting activity diminishes and eventually ceases. We model the quadrupolar magnetic distortion of the star, which is due to its ordered components primarily, as triaxial and very likely prolate. We address the question of whether the spin frequency ought to be detectable for precessing, bursting magnetars by constructing a specific model in which bursts happen randomly in time with random directions distributed in or between cones relative to a single symmetry axis. Within the context of these specific models, we find that there are precession geometries for which detecting the spin frequency is very unlikely.

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  4. Abstract The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium 1 , which is assumed to dominate the total extragalactic dispersion. Although the host-galaxy contributions to the dispersion measure appear to be small for most FRBs 2 , in at least one case there is evidence for an extreme magneto-ionic local environment 3,4 and a compact persistent radio source 5 . Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific-star-formation rate at a redshift of 0.241 ± 0.001. The estimated host-galaxy dispersion measure of approximately $${903}_{-111}^{+72}$$ 903 − 111 + 72 parsecs per cubic centimetre, which is nearly an order of magnitude higher than the average of FRB host galaxies 2,6 , far exceeds the dispersion-measure contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host-galaxy identifications. 
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  5. null (Ed.)
  6. Abstract We present new discoveries and results from long-term timing of 72 pulsars discovered in the Pulsar Arecibo L -band Feed Array (PALFA) survey, including precise determination of astrometric and spin parameters, and flux density and scatter broadening measurements at 1.4 GHz. Notable discoveries include two young pulsars (characteristic ages ∼30 kyr) with no apparent supernova remnant associations, three mode-changing, 12 nulling and two intermittent pulsars. We detected eight glitches in five pulsars. Among them is PSR J1939+2609, an apparently old pulsar (characteristic age ∼1 Gy), and PSR J1954+2529, which likely belongs to a newly emerging class of binary pulsars. The latter is the only pulsar among the 72 that is clearly not isolated: a nonrecycled neutron star with a 931 ms spin period in an eccentric ( e = 0.114) wide ( P b = 82.7 days) orbit with a companion of undetermined nature having a minimum mass of ∼0.6 M ⊙ . Since operations at Arecibo ceased in 2020 August, we give a final tally of PALFA sky coverage, and compare its 207 pulsar discoveries to the known population. On average, they are 50% more distant than other Galactic plane radio pulsars; PALFA millisecond pulsars (MSPs) have twice the dispersion measure per unit spin period than the known population of MSP in the plane. The four intermittent pulsars discovered by PALFA more than double the population of such objects, which should help to improve our understanding of pulsar magnetosphere physics. The statistics for these, rotating radio transients, and nulling pulsars suggest that there are many more of these objects in the Galaxy than was previously thought. 
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