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1. On the radio frequency dependence of the pulse delay phenomenon in PSR B0943+10

   https://doi.org/10.1093/mnras/stab472  

   Suleymanova, S A; Kazantsev, A N; Rankin, J M; Logvinenko, S V (March 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We report the result of measurements of a gradual shift of the integrated pulses towards later spin phase of the anomalous pulsar B0943+10 at high radio frequencies. We have used observations from the Arecibo Observatory and the GMRT at 327 and 325 MHz correspondingly. For the measurements, we have proposed a special method for calculating the correct positions of the partially merged two components of the pulse profile shape with significant temporal changes in their amplitude ratio. The exponential change in the pulse phase with an amplitude of 4 ms and characteristic time of about 1 h has been found. Comparison of our measurements at 325 and 327 MHz with those at the lower frequencies of 25–80, 62 and 112 MHz have shown that the character of the process does not depend on frequency across a wide frequency range. The result is very important for constraining the nature of the delay. It supports the assumption that the process results from changes in the vacuum gap near the surface of the pulsar. The further correlation between changes in the pulse phase and its intensity is discussed. 

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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. A Multifrequency Census of 100 Pulsars below 100 MHz with LWA: A Systematic Study of Flux Density, Spectra, Timing, Dispersion, Polarization, and Its Variation from a Decade of Observations

   https://doi.org/10.3847/1538-4357/adb97a  

   Kumar, P; Taylor, G B; Stovall, K; Dowell, J; White, S M (March 2025, The Astrophysical Journal)

   Abstract We present a census of 100 pulsars, the largest below 100 MHz, including 94 normal pulsars and six millisecond pulsars, with the Long Wavelength Array (LWA). Pulse profiles are detected across a range of frequencies from 26–88 MHz, including new narrowband profiles facilitating profile evolution studies, and breaks in pulsar spectra at low frequencies. We report mean flux density, spectral index, curvature, and low-frequency turnover-frequency measurements for 97 pulsars, including new measurements for 61 sources. Multifrequency profile widths are presented for all pulsars, including component spacing for 27 pulsars with two components. Polarized emission is detected from 27 of the sources (the largest sample at these frequencies) in multiple frequency bands, with one new detection. We also provide new timing solutions for five recently discovered pulsars. Low-frequency observations with the LWA are especially sensitive to propagation effects arising in the interstellar medium. We have made the most sensitive measurements of pulsar dispersion measures (DMs) and rotation measures, with median uncertainties of 2.9 × 10⁻⁴pc cm⁻³and 0.01 rad m⁻², respectively, and can track their variations over almost a decade, along with other frequency-dependent effects. This allows for stringent limits on average magnetic fields, with no variations detected above ∼20 nG. Finally, the census yields some interesting phenomena in individual sources, including the detection of frequency- and time-dependent DM variations in B2217+47, and the detection of highly circularly polarized emission from J0051+0423. 

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4. A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set

   https://doi.org/10.3847/1538-4357/acf4f2  

   Torne, Pablo; Liu, Kuo; Eatough, Ralph P.; Wongphechauxsorn, Jompoj; Cordes, James M.; Desvignes, Gregory; De Laurentis, Mariafelicia; Kramer, Michael; Ransom, Scott M.; Chatterjee, Shami; et al (November 2023, The Astrophysical Journal)

   Abstract In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz (λ= 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars—which typically exhibit steep emission spectra—are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (≲2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region. 

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5. Measurements of the Crab Pulsar’s Giant Radio Pulse Amplitude Power-law Index Using Low-frequency Arecibo and Green Bank Telescope Observations

   https://doi.org/10.3847/1538-4357/acca7f  

   Crawford, Fronefield; W. Lazio, T. Joseph; McEwen, Alexander; Deneva, Julia S.; Cordes, James M.; Spitler, Laura; Trainor, Ryan F. (May 2023, The Astrophysical Journal)

   Abstract We report two low-frequency measurements of the power-law index for the amplitudes of giant radio pulses from the Crab pulsar. The two observations were taken with the Arecibo and Green Bank radio telescopes at center frequencies of 327 MHz and 350 MHz, respectively. We find best-fit values for the differential power-law indexβ(where $\mathit{dN}/\mathit{dS}\propto S^{\beta }$andSis the pulse amplitude) of −2.63 ± 0.05 and −3.6 ± 0.5 from the Arecibo and Green Bank data sets, respectively. Both values are broadly consistent with other values previously measured for the Crab pulsar at low radio frequencies. These reported values may be useful in future giant pulse studies of the Crab pulsar. 

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