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1. Probing the Local Interstellar Medium with Scintillometry of the Bright Pulsar B1133 + 16

   https://doi.org/10.3847/1538-4357/ac460b  

   McKee, James W. ; Zhu, Hengrui ; Stinebring, Daniel R. ; Cordes, James M. ( March 2022 , The Astrophysical Journal)

   The interstellar medium hosts a population of scattering screens, most of unknown origin. Scintillation studies of pulsars provide a sensitive tool for resolving these scattering screens and a means of measuring their properties. In this paper, we report our analysis of 34 yr of Arecibo observations of PSR B1133 + 16, from which we have obtained high-quality dynamic spectra and their associated scintillation arcs, arising from the scattering screens located along the line of sight to the pulsar. We have identified six individual scattering screens that are responsible for the observed scintillation arcs, which persist for decades. Using the assumption that the scattering screens have not changed significantly in this time, we have modeled the variations in arc curvature throughout the Earth’s orbit and extracted information about the placement, orientation, and velocity of five of the six screens, with the highest-precision distance measurement placing a screen at just${5.46}_{-0.59}^{+0.54}$pc from the Earth. We associate the more distant of these screens with an underdense region of the Local Bubble.
2. Interstellar Scintillation and Polarization of PSR B0656+14 in the Monogem Ring

   https://doi.org/10.3847/1538-4357/ac9667  

   Yao, Jumei ; Coles, William A. ; Manchester, Richard N. ; Stinebring, Daniel R. ; Kramer, Michael ; Wang, Na ; Li, Di ; Zhu, Weiwei ; Feng, Yi ; Yuan, Jianping ; et al ( November 2022 , The Astrophysical Journal)

   Abstract High-sensitivity interstellar scintillation and polarization observations of PSR B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the spatial velocity are significantly different, with a separation of 19.°3 ± 0.°8, inconsistent with a previously published near-perfect alignment of 1° ± 2°. The two independent scattering regions are clearly defined in the secondary spectra, which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28 pc from PSR B0656+14 and 185 pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy A R to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delaymore »profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this.« less
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 observationmore »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. A MeerKAT look at the polarization of 47 Tucanae pulsars: magnetic field implications

   https://doi.org/10.1093/mnras/stac3248  

   Abbate, F. ; Possenti, A. ; Ridolfi, A. ; Venkatraman Krishnan, V. ; Buchner, S. ; Barr, E. D. ; Bailes, M. ; Kramer, M. ; Cameron, A. ; Parthasarathy, A. ; et al ( November 2022 , Monthly Notices of the Royal Astronomical Society)

   We present the polarization profiles of 22 pulsars in the globular cluster 47 Tucanae using observations from the MeerKAT radio telescope at UHF band (544–1088 MHz) and report precise values of dispersion measure (DM) and rotation measure (RM). We use these measurements to investigate the presence of turbulence in electron density and magnetic fields. The structure function of DM shows a break at ∼30 arcsec (∼0.6 pc at the distance of 47 Tucanae) that suggests the presence of turbulence in the gas in the cluster driven by the motion of wind-shedding stars. On the other hand, the structure function of RM does not show evidence of a break. This non-detection could be explained either by the limited number of pulsars or by the effects of the intervening gas in the Galaxy along the line of sight. Future pulsar discoveries in the cluster could help confirm the presence and localize the turbulence.
5. 4–8 GHz Fourier-domain Searches for Galactic Center Pulsars

   https://doi.org/10.3847/1538-4357/ac74c0  

   Suresh, Akshay ; Cordes, James M. ; Chatterjee, Shami ; Gajjar, Vishal ; Perez, Karen I. ; Siemion, Andrew P. V. ; Lebofsky, Matt ; MacMahon, David H. E. ; Ng, Cherry ( July 2022 , The Astrophysical Journal)

   The Galactic Center (GC), with its high density of massive stars, is a promising target for radio transient searches. In particular, the discovery and timing of a pulsar orbiting the central supermassive black hole (SMBH) of our galaxy will enable stringent strong-field tests of gravity and accurate measurements of SMBH properties. We performed multiepoch 4–8 GHz observations of the inner ≈15 pc of our galaxy using the Robert C. Byrd Green Bank Telescope in 2019 August–September. Our investigations constitute the most sensitive 4–8 GHz GC pulsar survey conducted to date, reaching down to a 6.1 GHz pseudo-luminosity threshold of ≈1 mJy kpc²for a pulse duty cycle of 2.5%. We searched our data in the Fourier domain for periodic signals incorporating a constant or linearly changing line-of-sight pulsar acceleration. We report the successful detection of the GC magnetar PSR J1745−2900 in our data. Our pulsar searches yielded a nondetection of novel periodic astrophysical emissions above a 6σdetection threshold in harmonic-summed power spectra. We reconcile our nondetection of GC pulsars with inadequate sensitivity to a likely GC pulsar population dominated by millisecond pulsars. Alternatively, close encounters with compact objects in the dense GC environment may scatter pulsars away from the GC.more »The dense central interstellar medium may also favorably produce magnetars over pulsars.

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