The Anomalous Acceleration of PSR J2043+1711: Long-Period Orbital Companion or Stellar Flyby?

TL;DR

This paper investigates the cause of the anomalous acceleration of pulsar PSR J2043+1711, exploring whether it is due to a stellar flyby or a long-period orbital companion, with implications for understanding pulsar environments.

Contribution

It proposes and evaluates two plausible explanations for the pulsar's anomalous acceleration: a chance stellar flyby and a potential hierarchical triple system with a long-period companion.

Findings

A nearby star is unlikely to be gravitationally bound to the pulsar.

A possible orbital companion has an estimated period of 80 kyr and a mass around 0.3 solar masses.

Further observations are needed to confirm the companion or flyby scenario.

Abstract

Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 $\pm$ 0.8 mm/s/yr, which deviates from the acceleration predicted by equilibrium Milky Way models at a $4\sigma$ level. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the Milky Way interacting with orbiting dwarf galaxies ($\sim$1 mm/s/yr), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in \textit{Gaia} DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6\%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 80 kyr, a companion mass of 0.3 $M_\odot$ (indicative of a white dwarf or low-mass star), and a semi-major axis of 2000 AU. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios.