State transitions triggered by inverse magnetic field: probably applied in high-mass X-ray binaries?

TL;DR

This paper investigates whether inverse magnetic field accretion can trigger state transitions in X-ray binaries, focusing on the magnetic field magnification process in realistic systems like Cyg X-1.

Contribution

It demonstrates that a strong initial magnetic field is necessary for effective magnetic field dragging and magnification in high-mass X-ray binaries.

Findings

Strong initial magnetic fields ($10^2$-$10^3$ G) are required for magnetic field magnification.

The mechanism is likely applicable to high-mass X-ray binaries like Cyg X-1.

Magnetic field accretion could trigger state transitions in such systems.

Abstract

Previous works suggested that the state transitions in an X-ray binary can be triggered by accreting inverse magnetic field from its companion star. A key point of this mechanism is the accretion and magnification of large-scale magnetic fields from outer boundary of a thin disk. However, how such a process can be realized is still an open question. In this work, we check this issue in a realistic X-ray binary system. According to our calculations, a quite strong initial magnetic field $B\sim 10^2-10^3$ G is required in order to assure that the large-scale magnetic field can be effectively dragged inward and magnified with the accretion of gas. Thus, such a picture probably can be present in high-mass X-ray binaries possessing strong stellar magnetic field, e.g., Cyg X-1.