The PSR J0435+3233 Triple System

Abstract

Abstract The detailed evolution of triple star systems is complicated and poorly known. Using archived optical/infrared and gamma-ray data, we identified the pulsar PSR J0435+3233 as a gamma-ray pulsar in a hierarchical triple system, with a helium white dwarf (WD) as a close inner binary companion and a Sun-like star as the distant tertiary. PSR J0435+3233 and the WD companion are in a circular orbit with a period of P orb1  = 8.0 days and an eccentricity of e = 0.00016. The tertiary is a G-type subgiant with a mass of 0.98(12) M ⊙ at a distance of 2.1(4) kpc from the Earth. By simultaneously fitting the observed spin-period variations of the gamma-ray emission (over 16.7 yr) and radio emission (over 4.9 yr) from PSR J0435+3233, the changes in the inner orbital parameters, the Shapiro delay, Gaia astrometry, and the outer companion mass, we determined the outer elliptical orbit for the tertiary, with a period P orb2  = 73.5 yr and an eccentricity e 2  = 0.598. The outer orbit is either nearly perpendicular to the inner orbit with a mutual inclination of ∼85 ∘ , or moderately inclined by ∼54 ∘ . For the former geometry, the pulsar, the WD, and the tertiary star have masses of 1.16(5) M ⊙ , 0.273(8) M ⊙ , and 0.91(5) M ⊙ , respectively; for the latter geometry, the corresponding masses are 1.34(15) M ⊙ , 0.305(23) M ⊙ , and 1.13(7) M ⊙ . This is a unique triple system for detailed multiband observations and for studying the evolutionary path and dynamic processes of a primordial triple star system. It will ultimately evolve into a system consisting of a neutron star and two WDs.