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1. Deep Synoptic Array Science: Polarimetry of 25 New Fast Radio Bursts Provides Insights into Their Origins

   https://doi.org/10.3847/1538-4357/ad275e  

   Sherman, Myles B. ; Connor, Liam ; Ravi, Vikram ; Law, Casey ; Chen, Ge ; Catha, Morgan ; Faber, Jakob T. ; Hallinan, Gregg ; Harnach, Charlie ; Hellbourg, Greg ; et al ( March 2024 , The Astrophysical Journal)

   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.

    

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2. The NANOGrav 12.5 yr Data Set: Polarimetry and Faraday Rotation Measures from Observations of Millisecond Pulsars with the Green Bank Telescope

   https://doi.org/10.3847/1538-4357/ac4045  

   Wahl, H. M. ; McLaughlin, M. A. ; Gentile, P. A. ; Jones, M. L. ; Spiewak, R. ; Arzoumanian, Z. ; Crowter, K. ; Demorest, P. B. ; DeCesar, M. E. ; Dolch, T. ; et al ( February 2022 , The Astrophysical Journal)

   Abstract In this work, we present polarization profiles for 23 millisecond pulsars observed at 820 and 1500 MHz with the Green Bank Telescope as part of the NANOGrav pulsar timing array. We calibrate the data using Mueller matrix solutions calculated from observations of PSRs B1929+10 and J1022+1001. We discuss the polarization profiles, which can be used to constrain pulsar emission geometry, and present both the first published radio polarization profiles for nine pulsars and the discovery of very low-intensity average profile components (“microcomponents”) in four pulsars. We obtain the Faraday rotation measures for each pulsar and use them to calculate the Galactic magnetic field parallel to the line of sight for different lines of sight through the interstellar medium. We fit for linear and sinusoidal trends in time in the dispersion measure and Galactic magnetic field and detect magnetic field variations with a period of 1 yr in some pulsars, but overall find that the variations in these parameters are more consistent with a stochastic origin. 

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3. Radio Pulse Profiles and Polarization of the Terzan 5 Pulsars

   https://doi.org/10.3847/1538-4357/aca156  

   Martsen, Ashley R. ; Ransom, Scott M. ; DeCesar, Megan E. ; Freire, Paulo C. C. ; Hessels, Jason W. T. ; Ho, Anna Y. Q. ; Lynch, Ryan S. ; Stairs, Ingrid H. ; Wang, Yuankun ( December 2022 , The Astrophysical Journal)

   Terzan 5 is a rich globular cluster within the galactic bulge containing 39 known millisecond pulsars, the largest known population of any globular cluster. These faint pulsars do not have sufficient signal-to-noise ratio (S/N) to measure reliable flux density or polarization information from individual observations in general. We combined over 5.2 days of archival data, at 1500 and 2000 MHz, taken with the Green Bank Telescope over the past 12 years. We created high-S/N profiles for 32 of the pulsars and determined precise rotation measures (RMs) for 28. We used the RMs, pulsar positions, and dispersion measures to map the projected parallel component of the Galactic magnetic field toward the cluster. The 〈B_∣∣〉 shows a rough gradient of ∼6 nG arcsec⁻¹(∼160 nG pc⁻¹) or, fractionally, a change of ∼20% in the R.A. direction across the cluster, implying Galactic magnetic field variability at sub-parsec scales. We also measured average flux densitiesS_νfor the pulsars, ranging from ∼10μJy to ∼2 mJy, and an average spectral indexα= −1.35, whereS_ν∝ν^α. This spectral index is flatter than most known pulsars, likely a selection effect due to the high frequencies used in pulsar searches to mitigate dispersion and scattering. We used flux densities from each observation to constrain the scintillation properties toward the cluster, finding strong refractive modulation on timescales of months. The inferred pulsar luminosity function is roughly power law, with slope$(d\log N)/(d\log L)=-1$at the high-luminosity end. At the low-luminosity end, there are incompleteness effects, implying that Terzan 5 contains many more pulsars.

    

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4. Polarization measurements of Arecibo-sky pulsars: Faraday rotations and emission-beam analyses

   https://doi.org/10.1093/mnras/stad2182  

   Rankin, Joanna ; Venkataraman, Arun ; Weisberg, Joel M. ; Curtin, Alice P. ( July 2023 , Monthly Notices of the Royal Astronomical Society)

   We present Faraday rotation measure (RM) values derived at L and P bands as well as some 60 Stokes-parameter profiles, both determined from our long-standing Arecibo dual-frequency pulsar polarimetry programmes. Many of the RM measurements were carried out towards the inner Galaxy and the anticentre on pulsars with no previous determination, while others are remeasurements intended to confirm or improve the accuracy of existing values. Stokes-parameter profiles are displayed for the 58 pulsars for which no meaningful Stokes profile at lower frequency is available and 4 without a high-frequency pair. This is a population that includes many distant pulsars in the inner Galaxy. A number of these polarized pulse profiles exhibit clear interstellar-scattering tails; none the less, we have attempted to interpret the associated emission-beam structures and to provide morphological classifications and geometrical models where possible.

    

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5. Discovery of PSR J0523-7125 as a Circularly Polarized Variable Radio Source in the Large Magellanic Cloud

   https://doi.org/10.3847/1538-4357/ac61dc  

   Wang, Yuanming ; Murphy, Tara ; Kaplan, David L. ; Klinner-Teo, Teresa ; Ridolfi, Alessandro ; Bailes, Matthew ; Crawford, Fronefield ; Dai, Shi ; Dobie, Dougal ; Gaensler, B. M. ; et al ( May 2022 , The Astrophysical Journal)

   Abstract We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ∼20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cm −3 , and rotation measure (RM) of +456 rad m −2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523−7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ∼1 mJy at 1400 MHz and ∼25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ −3, where S ν ∝ ν α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds. 

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