The Binary Companion of Young, Relativistic Pulsar J1906+0746 (1411.1518v1)

Abstract: PSR J1906+0746 is a young pulsar in the relativistic binary with the second-shortest known orbital period, of 3.98 hours. We here present a timing study based on five years of observations, conducted with the 5 largest radio telescopes in the world, aimed at determining the companion nature. Through the measurement of three post-Keplerian orbital parameters we find the pulsar mass to be 1.291(11) M_sol, and the companion mass 1.322(11) M_sol respectively. These masses fit well in the observed collection of double neutron stars, but are also compatible with other white dwarfs around young pulsars such as J1906+0746. Neither radio pulsations nor dispersion-inducing outflows that could have further established the companion nature were detected. We derive an HI-absorption distance, which indicates that an optical confirmation of a white dwarf companion is very challenging. The pulsar is fading fast due to geodetic precession, limiting future timing improvements. We conclude that young pulsar J1906+0746 is likely part of a double neutron star, or is otherwise orbited by an older white dwarf, in an exotic system formed through two stages of mass transfer.

• The paper’s main contribution is the precise measurement of three post-Keplerian parameters to accurately constrain the masses of pulsar J1906+0746 and its companion.
• It employs five years of radio telescope data and precision timing methods to reveal a relativistic binary system with a 3.98-hour orbital period.
• The findings offer a natural laboratory for testing General Relativity and exploring evolutionary pathways in young compact binary systems.

The Young, Relativistic Binary Pulsar J1906+0746

This paper provides an in-depth analysis of PSR J1906+0746, a young pulsar in a relativistic binary system with a notably short orbital period of 3.98 hours. Utilizing extensive data collected over five years from the world's largest radio telescopes, the paper aimed to elucidate the nature of its binary companion. Through precision pulsar timing methods, the paper accurately measured three post-Keplerian parameters: the advance of periastron ($\dot{\omega}$), the gravitational redshift/time dilation parameter ($\gamma$), and the orbital period derivative ($\dot{P}_b$). This enabled the authors to constrain the pulsar mass to 1.291(11)$M_\odot$ and the companion mass to 1.322(11)$M_\odot$.

Key Findings and Numerical Results

The derived masses for PSR J1906+0746 and its companion fit well within the known population of double neutron star systems (DNS), providing a compelling case that the companion itself may be a neutron star. However, the possibility of the companion being a massive white dwarf cannot be dismissed based merely on mass estimates, as the masses are also comparable to some white dwarf systems with young pulsars.

An important aspect of this paper is the observation of the pulsar's fading due to geodetic precession, which will likely limit future timing precision. This fading highlights the dynamic environment of such systems and provides a rare look at young pulsars in close binary environments.

Implications and Future Research

The implications of this research stretch across both practical and theoretical domains. In terms of practical applications, the precise measurement of post-Keplerian parameters enhances our understanding of relativistic effects in strong gravitational fields, offering further data to test General Relativity. The detection of post-Keplerian parameters suggests that PSR J1906+0746 may serve as a natural laboratory for testing alternative theories of gravity, especially in its interaction with either another neutron star or a white dwarf.

Theoretically, this paper elucidates different evolutionary pathways that such systems may undergo, emphasizing the diversity in compact binary evolution scenarios. The results suggest the need for further exploration into the formation mechanisms of young pulsars in binary systems, particularly looking towards mass transfer processes and supernova kicks involved.

The paper’s refined mass estimates also open up potential areas of exploration regarding the evolutionary history of binary systems containing neutron stars and higher-mass white dwarfs. If J1906+0746 is indeed a DNS system, it will contribute to statistical studies seeking to understand the formation rates of such systems and their spatial distribution within the Galaxy.

Future research endeavors could focus on leveraging multi-wavelength observations to identify the companion's nature definitively. Despite the challenges of optical detection due to expected faintness and line-of-sight extinction, advancements in astrometric methods like Very Long Baseline Interferometry (VLBI) could eventually resolve ambiguities in the system's kinematic properties, such as proper motion and distance, which would be instrumental in refining our theoretical models.

In conclusion, the revelations from the pulsar J1906+0746 set a distinctive example of the complexities involved in the evolution and detection of close binary systems, and offer substantial material for the continued investigation into their dynamic characteristics and formation histories.