2020MNRAS.494...44H

The application of standard accretion theory to observations of X-ray binaries provides valuable insights into neutron star (NS) properties, such as their spin period and magnetic field. However, most studies concentrate on relatively old systems, where the NS is in its late propeller, accretor, or nearly spin equilibrium phase. Here, we use an analytic model from standard accretion theory to illustrate the evolution of high-mass X-ray binaries (HMXBs) early in their life. We show that a young NS is unlikely to be an accretor because of the long duration of ejector and propeller phases. We apply the model to the recently discovered ∼4000 yr old HMXB XMMU J051342.6-672412 and find that the system's NS, with a tentative spin period of 4.4 s, cannot be in the accretor phase and has a magnetic field B > a few x 10¹³ G, which is comparable to the magnetic field of many older HMXBs and is much higher than the spin equilibrium inferred value of a few x 10¹¹ G. The observed X-ray luminosity could be the result of thermal emission from a young cooling magnetic NS or a small amount of accretion that can occur in the propeller phase.