Refined Mass and Geometric Measurements of the High-Mass PSR J0740+6620

Abstract: We report results from continued timing observations of PSR J0740+6620, a high-mass, 2.8-ms radio pulsar in orbit with a likely ultra-cool white dwarf companion. Our data set consists of combined pulse arrival-time measurements made with the 100-m Green Bank Telescope and the Canadian Hydrogen Intensity Mapping Experiment telescope. We explore the significance of timing-based phenomena arising from general-relativistic dynamics and variations in pulse dispersion. When using various statistical methods, we find that combining $\sim 1.5$ years of additional, high-cadence timing data with previous measurements confirms and improves upon previous estimates of relativistic effects within the PSR J0740+6620 system, with the pulsar mass $m_{\rm p} = 2.08^{+0.07}_{-0.07}$ M$\odot$ (68.3\% credibility) determined by the relativistic Shapiro time delay. For the first time, we measure secular variation in the orbital period and argue that this effect arises from apparent acceleration due to significant transverse motion. After incorporating contributions from Galactic differential rotation and off-plane acceleration in the Galactic potential, we obtain a model-dependent distance of $d = 1.14^{+0.17}{-0.15}$ kpc (68.3\% credibility). This improved distance confirms the ultra-cool nature of the white dwarf companion determined from recent optical observations. We discuss the prospects for future observations with next-generation facilities, which will likely improve the precision on $m_{\rm p}$ for J0740+6620 by an order of magnitude within the next few years.

• The paper achieves a precise mass measurement of 2.08±0.07 M☉ using the Shapiro delay, establishing PSR J0740+6620 as one of the most massive neutron stars known.
• It employs comprehensive pulse arrival-time observations from GBT and CHIME to determine detailed orbital and geometric parameters.
• The refined measurements challenge existing dense-matter equations of state, paving the way for improved models of neutron star structure and evolution.

Refined Mass and Geometric Measurements of the High-Mass PSR J0740+6620

The paper "Refined Mass and Geometric Measurements of the High-Mass PSR J0740+6620" presents an analytical study focusing on advanced observational measurements of PSR J0740+6620. This pulsar is distinguished by its significant mass and brief rotation period of 2.8 milliseconds, existing binarily with an ultra-cool white dwarf. The research utilizes an extensive dataset compiled from pulse arrival-time observations captured via the Green Bank Telescope (GBT) and the Canadian Hydrogen Intensity Mapping Experiment (CHIME).

Key Findings

One of the pivotal results of this study is the precise determination of the pulsar mass, quoted as $m_{\rm p} = 2.08^{+0.07}_{-0.07}$ M_$\odot$ at a credibility interval of 68.3%. This was achieved using the Shapiro time delay, a relativistic effect which provides insight into the mass of the pulsar. This measurement establishes PSR J0740+6620's status as one of the most massive neutron stars known to date, offering vital constraints for the equation of state (EoS) for dense matter.

The distance to the pulsar system was rigorously calculated through secular variations in the orbital period, resulting in an improved model-dependent measure of $d = 1.14^{+0.17}_{-0.15}$ kpc. This solution was validated by accounting for apparent acceleration due to transverse motion and other Galactic contributions, thus furnishing an end-to-end verification of the model.

Implications and Future Directions

The refined measurements have substantial implications for astrophysics, particularly in validating or refuting various neutron star EoS models that predict the behavior of matter at nuclear densities. Larger masses like those of PSR J0740+6620 challenge EoS models that predict lower maximum neutron star masses, refining our understanding of stellar evolution and matter under extreme conditions.

Based on these findings, the study highlights prospects for enabling more refined pulsar mass and geometry metrics. Upcoming advancements in telescope facilities and receiver technologies, like the next-generation Very Large Array (ngVLA) and the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD), promise unprecedented resolution in TOA precision, which could further reduce uncertainties in similar future analyses. Hence, consistent and high-cadence observations will remain integral in refining these measurements.

In essence, this paper contributes significantly to the field of high-energy astrophysics by delivering precise measurements critical for assessing the fundamental properties of neutron stars. The study lays a robust groundwork for future observations and theoretical explorations pertinent to the enigmatic interior states of neutron stars.