Timing analysis for 20 millisecond pulsars in the Parkes Pulsar Timing Array (1510.04434v1)

Abstract: We present timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array. The precision of the parameter measurements in these models has been improved over earlier results by using longer data sets and modelling the non-stationary noise. We describe a new noise modelling procedure and demonstrate its effectiveness using simulated data. Our methodology includes the addition of annual dispersion measure (DM) variations to the timing models of some pulsars. We present the first significant parallax measurements for PSRs J1024-0719, J1045-4509, J1600-3053, J1603-7202, and J1730-2304, as well as the first significant measurements of some post-Keplerian orbital parameters in six binary pulsars, caused by kinematic effects. Improved Shapiro delay measurements have resulted in much improved pulsar mass measurements, particularly for PSRs J0437-4715 and J1909-3744 with $M_p=1.44\pm0.07$ $M_\odot$ and $M_p=1.47\pm0.03$ $M_\odot$ respectively. The improved orbital period-derivative measurement for PSR J0437-4715 results in a derived distance measurement at the 0.16% level of precision, $D=156.79\pm0.25$ pc, one of the most fractionally precise distance measurements of any star to date.

• The paper presents refined timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array using longer data sets and a novel non-stationary noise modeling procedure to improve parameter precision.
• The study achieved significant parallax measurements for several pulsars, leading to improved distance estimations, including one of the most precise distance measurements for any star (PSR J0437-4715).
• Enhanced timing models and improved parameter measurements, such as pulsar masses derived from Shapiro delay, advance capabilities for nanohertz gravitational wave detection and tests of fundamental physics like general relativity.

Analysis and Findings from Pulsar Timing in the Parkes Pulsar Timing Array

This paper presents a comprehensive paper of timing models for 20 millisecond pulsars (MSPs) observed as part of the Parkes Pulsar Timing Array (PPTA). The central aim of this work is to improve the precision of parameter measurements by utilizing longer data sets and refining noise modeling techniques. The research introduces a novel noise modeling procedure tailored for non-stationary noise, evaluating its effectiveness through simulated data. Furthermore, the paper incorporates annual dispersion measure (DM) variations into timing models for certain pulsars, leading to the first significant parallax measurements for several pulsars and improved mass measurements due to enhanced Shapiro delay assessments.

Key Findings

1. Noise Modeling and Parameter Estimation:
   • The paper advances pulsar timing models by addressing non-stationary noise using a new "split-Cholesky" algorithm. This method constructs separate covariance matrices for frequency-independent noise and DM noise, significantly supporting parameter measurements’ accuracy.
   • A detailed model for DM variations was developed for each pulsar, enhancing the overall timing model accuracy.
2. Parallax and Distance Measurements:
   • The research reports critical parallax measurements for pulsars such as J1024$-$0719, J1045$-$4509, J1600$-$3053, J1603$-$7202, and J1730$-$2304. Parallax values were corrected for Lutz-Kelker bias, providing potentially more precise distance estimations than those derived from dispersion measure models alone.
   • Notably, the distance to PSR J0437$-$4715 was determined with 0.16% precision, presenting one of the most precise distance measurements for any star.
3. Implications for Astrophysics and Gravitational Wave Detection:
   • Improved timing models enhance capabilities for gravitational wave detection, particularly in the nanohertz frequency range, a primary goal for PTAs. Accurate distances are crucial for leveraging the pulsar term in gravitational wave source localization.
   • The enhancement in pulsar mass measurements, particularly through refined Shapiro delay data, are critical for testing theoretical predictions such as those involving general relativity.

Numerical and Theoretical Highlights

• The paper achieved significant enhancements in the precision of pulsar mass and distance measurements. For instance, PSR J0437$-$4715's mass was refined to 1.44±0.07 M☉ with considerable implications for testing the neutron star equation of state.
• The novel noise modeling approach demonstrated superior performance in maintaining unbiased estimates with correct parameter uncertainties across simulations, an improvement over previous methods such as Bayessian analyses under non-stationary noise conditions.

Future Trajectories

The methodologies developed in this paper could be extended to future PPTA data releases, aiding in refining gravitational wave searches and testing fundamental physics. The novel approach to pulsar timing models, particularly with non-stationary noise elements, lays the groundwork for further developments in the field, potentially impacting areas like interstellar medium studies and pulsar-based timekeeping.

Overall, the paper represents a significant technical contribution to pulsar astrophysics, enhancing the robustness of timing models and advancing the precision in the estimation of astrophysical parameters critical for varied applications in space science.