2016/08/06 by Wen-Cong Chen, Philipp Podsiadlowski
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Eddy current brake #Gamma-ray bursts and supernovae #Magnetic field #Magnetic flux #Neutron star #Observable #Stars #Stellar evolution #White dwarf #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.3847/0004-637x/830/2/131
published as ApJ, 2016, 830,131 · 10 pages, 9 figures, 2 tables, accepted for publication in ApJ
arxiv created 2016/08/06 · openalex created_date 2016/08/23 · openalex publication_date 2016/10/18 · arxiv updated 2016/10/24 · openalex updated_date 2026/08/05
ABSTRACT It is generally believed that ultracompact X-ray binaries (UCXBs) evolved from binaries consisting of a neutron star accreting from a low-mass white dwarf (WD) or helium star where mass transfer is driven by gravitational radiation. However, the standard WD evolutionary channel cannot produce the relatively long-period (40–60 minutes) UCXBs with a high time-averaged mass-transfer rate. In this work, we explore an alternative evolutionary route toward UCXBs, where the companions evolve from intermediate-mass Ap/Bp stars with an anomalously strong magnetic field (100–10,000 G). Including the magnetic braking caused by the coupling between the magnetic field and an irradiation-driven wind induced by the X-ray flux from the accreting component, we show that intermediate-mass X-ray binaries (IMXBs) can evolve into UCXBs. Using the MESA code, we have calculated evolutionary sequences for a large number of IMXBs. The simulated results indicate that, for a small wind-driving efficiency f = 10 −5 , the anomalous magnetic braking can drive IMXBs to an ultra-short period of 11 minutes. Comparing our simulated results with the observed parameters of 15 identified UCXBs, the anomalous magnetic braking evolutionary channel can account for the formation of seven and eight sources with f = 10 −3 , and 10 −5 , respectively. In particular, a relatively large value of f can fit three of the long-period, persistent sources with a high mass-transfer rate. Though the proportion of Ap/Bp stars in intermediate-mass stars is only 5%, the lifetime of the UCXB phase is ≳2 Gyr, producing a relatively high number of observable systems, making this an alternative evolutionary channel for the formation of UCXBs.