The Binary Companion of Young, Relativistic Pulsar J1906+0746

TL;DR

This study uses five years of radio observations to analyze the binary system of young pulsar J1906+0746, aiming to determine whether its companion is a neutron star or a white dwarf, but definitive identification remains challenging.

Contribution

The paper provides detailed timing measurements and mass estimates for the pulsar and its companion, exploring their possible nature and the system's formation history.

Findings

Pulsar mass estimated at 1.291 solar masses.

Companion mass estimated at 1.322 solar masses.

No radio pulsations detected from the companion.

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.