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1. Algorithmic Pulsar Timing

   https://doi.org/10.3847/1538-3881/ac403e  

   Phillips, Camryn; Ransom, Scott (January 2022, The Astronomical Journal)

   Abstract Pulsar timing is a process of iteratively fitting pulse arrival times to constrain the spindown, astrometric, and possibly binary parameters of a pulsar, by enforcing integer numbers of pulsar rotations between the arrival times. Phase connection is the process of unambiguously determining those rotation numbers between the times of arrival while determining a pulsar timing solution. Pulsar timing currently requires a manual process of step-by-step phase connection performed by individuals. In an effort to quantify and streamline this process, we created the Algorithmic Pulsar Timer (APT), an algorithm that can accurately phase connect and time isolate pulsars. Using the statistical F-test and knowledge of parameter uncertainties and covariances, the algorithm decides what new data to include in a fit, when to add additional timing parameters, and which model to attempt in subsequent iterations. Using these tools, the algorithm can phase-connect timing data that previously required substantial manual effort. We tested the algorithm on 100 simulated systems, with a 99% success rate. APT combines statistical tests and techniques with a logical decision-making process, very similar to the manual one used by pulsar astronomers for decades, and some computational brute force, to automate the often tricky process of isolated pulsar phase connection, setting the foundation for automated fitting of binary pulsar systems. 

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2. Pulsar observations at low frequencies: applications to pulsar timing and solar wind models

   https://doi.org/10.1093/mnras/stac316  

   Kumar, P.; White, S. M.; Stovall, K.; Dowell, J.; Taylor, G. B. (February 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Efforts are underway to use high-precision timing of pulsars in order to detect low-frequency gravitational waves. A limit to this technique is the timing noise generated by dispersion in the plasma along the line of sight to the pulsar, including the solar wind. The effects due to the solar wind vary with time, influenced by the change in solar activity on different time-scales, ranging up to ∼11 yr for a solar cycle. The solar wind contribution depends strongly on the angle between the pulsar line of sight and the solar disc, and is a dominant effect at small separations. Although solar wind models to mitigate these effects do exist, they do not account for all the effects of the solar wind and its temporal changes. Since low-frequency pulsar observations are most sensitive to these dispersive delays, they are most suited to test the efficacy of these models and identify alternative approaches. Here, we investigate the efficacy of some solar wind models commonly used in pulsar timing using long-term, high-cadence data on six pulsars taken with the Long Wavelength Array, and compare them with an operational solar wind model. Our results show that stationary models of the solar wind correction are insufficient to achieve the timing noise desired by pulsar timing experiments, and we need to use non-stationary models, which are informed by other solar wind observations, to obtain accurate timing residuals. 

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3. The Green Bank North Celestial Cap Pulsar Survey. III. 45 New Pulsar Timing Solutions

   https://doi.org/10.3847/1538-4357/aabf8a  

   Lynch, Ryan S.; Swiggum, Joseph K.; Kondratiev, Vlad I.; Kaplan, David L.; Stovall, Kevin; Fonseca, Emmanuel; Roberts, Mallory S.; Levin, Lina; DeCesar, Megan E.; Cui, Bingyi; et al (June 2018, The Astrophysical Journal)
4. Did GW170817 Harbor a Pulsar?

   https://doi.org/10.3847/2041-8213/ab3f2c  

   Ramirez-Ruiz, Enrico; Andrews, Jeff J.; Schrøder, Sophie L. (September 2019, The Astrophysical Journal)
5. Algorithmic Pulsar Timer for Binaries

   https://doi.org/10.3847/1538-4357/ad1ce9  

   Taylor, Jackson; Ransom, Scott; Padmanabh, Prajwal V. (March 2024, The Astrophysical Journal)

   Abstract Pulsar timing is a powerful tool that, by accounting for every rotation of a pulsar, precisely measures the spin frequency, spin frequency derivatives, astrometric position, binary parameters when applicable, properties of the interstellar medium, and potentially general relativistic effects. Typically, this process demands fairly stringent scheduling requirements for monitoring observations as well as deep domain knowledge to “phase connect” the timing data. We present an algorithm that automates the pulsar-timing process for binary pulsars, whose timing solutions have an additional level of complexity, although the algorithm works for isolated pulsars as well. Using the statisticalF-test and the quadratic dependence of the reducedχ²near a minimum, the global rotation count of a pulsar can be determined efficiently and systematically. We have used our algorithm to establish timing solutions for two newly discovered binary pulsars, PSRs J1748−2446aq and J1748−2446at, in the globular cluster Terzan 5, using ∼70 Green Bank Telescope observations from the last 13 yr. 

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