A promising formation channel for symbiotic X-ray binaries: cases of IGR J17329-2731 and 4U 1700+24

TL;DR

This paper explores a new formation channel for symbiotic X-ray binaries involving accretion-induced collapse of magnetic white dwarfs, showing it can produce highly magnetized neutron stars consistent with observations.

Contribution

It demonstrates that magnetic confinement during white dwarf accretion significantly influences the formation of highly magnetized neutron stars in symbiotic X-ray binaries via AIC.

Findings

Magnetic confinement increases mass accumulation efficiency at low transfer rates.

AIC of magnetic white dwarfs can produce long-lived, highly magnetized neutron stars.

Parameter space for formation shifts to lower initial masses and periods with magnetic effects.

Abstract

Recent observations demonstrate that the symbiotic X-ray binary (SyXB) IGR J17329-2731 contains a highly magnetized neutron star (NS) which accretes matter through the wind from its giant star companion, and suggest that 4U 1700+24 may also have a highly magnetized NS. Accretion-induced collapse (AIC) from oxygen-neon-magnesium white dwarf (ONeMg WD) + red giant (RG) star binaries is one promising channel to form these SyXBs, while other long standing formation channels have difficulties to produce these SyXBs. By considering non-magnetic and magnetic ONeMg WDs, I investigate the evolution of ONeMg WD + RG binaries with the MESA stellar evolution code for producing SyXBs with non-magnetic or magnetized NSs. In the pre-AIC evolution with magnetic confinement, the mass accumulation efficiency of the accreting WD is increased at low mass transfer rate compared to the non-magnetic case. The newborn NSs formed via AIC of highly magnetized WDs could inherit the large magnetic field through conservation of magnetic flux, and the systems could have a long age compatible with that of the red giant companions. These young and highly magnetized NSs could accrete matters from the stellar wind of the giant companions to that shine as those observed SyXBs, and could preserve their high magnetic field during this time. The MESA calculation results show that the initial parameter (initial RG mass and orbital period) space for the AIC with magnetic confinement to form SyXBs with highly magnetized NSs shifts to be lower and narrower compared to that of the no magnetic confinement case.