Ultracompact X-ray binaries with He star companions

Abstract

Ultra-compact X-ray binaries (UCXBs) are low-mass X-ray binaries with hydrogen-deficient mass-donors and ultra-short orbital periods. They have been suggested to be the potential Laser Interferometer Space Antenna (LISA) sources in the low-frequency region. Several channels for the formation of UCXBs have been proposed so far. In this article, we carried out a systematic study on the He star donor channel, in which a neutron star (NS) accretes matter from a He main-sequence (MS) star through Roche-lobe overflow, where the mass-transfer is driven by the gravitational wave radiation. Firstly, we followed the long-term evolution of the NS+He MS binaries by employing the stellar evolution code Modules for Experiments in Stellar Astrophysics, and thereby obtained the initial parameter spaces for the production of UCXBs. We then used these results to perform a detailed binary population synthesis approach to obtain the Galactic rates of UCXBs through this channel. We estimate the Galactic rates of UCXBs appearing as LISA sources to be $\sim 3.1-11.9\, \rm Myr^{-1}$ through this channel, and the number of such UCXB-LISA sources in the Galaxy can reach about 1 − 26 calibrated by observations. The present work indicates that the He star donor channel may contribute significantly to the Galactic UCXB formation rate. We found that the evolutionary tracks of UCXBs through this channel can account for the location of the five transient sources with relatively long orbital periods quite well. We also found that such UCXBs can be identified by their locations in the mass-transfer rate versus the orbital period diagram.

Formation of black widows through ultra-compact X-ray binaries with He star companions

“…It has been suggested that PSR J1719-1438 may be formed from ultracompact X-ray binaries (UCXBs; e.g. Nelemans & Jonker 2010;Heinke et al 2013;Wang et al 2021), but the standard UCXB channel with MS star companions hardly reproduces this system within the Hubble time (e.g. Bailes et al 2011;van Haaften et al 2012).…”

“…Romani et al 2012;Romani, Filippenko & Cenko 2015). Wang et al (2021) studied the formation and evolution of UCXBs with He star companions systematically. They found that this channel can explain the formation of five transient sources with relatively long orbital periods.…”

“…When the NS+He star system experienced the UCXB stage and the mass-transfer rate drops to less than a critical value on the declining stage (see Fig. 4 in Wang et al 2021), this system will appear to be a transient source due to the thermal-viscous instability of accretion disks (e.g. King, Kolb & BurderiLasota 1996;Dubus et al 1999;Lasota et al 2008).…”

“…Following the work of Wang et al (2021), we will explore the origin of BWs with M 2 0.01 M ⊙ by considering the evaporation process based on the UCXB channel. In Section 2, we described the numerical methods and assumptions for the binary evolution simulations.…”

Resurrection of Non-thermal Emissions from Type Ib/c Supernova Remnants

“…However, a smoking-gun observational evidence for a Type Ib/c supernova remnant (SNR) is still ab-sent. Type Ib/c SNe are also noteworthy from the perspective of the production of neutron star systems and millisecond pulsars (e.g., Tauris & Savonije 1999;van den Heuvel 2009;Wang et al 2021), and theoretical studies of Type Ib/c SNe have developed rapidly in the past few decades (e.g., Smith 2017;Yoon 2017;Woosley 2019;Ertl et al 2020;Woosley et al 2020Woosley et al , 2021. On the other hand, detailed evolution and emission models for Type Ib/c SNRs are still scarce in the literature, which however are essential for their future identifications and a comprehensive understanding of the SNR population.…”