Work

Gaussian process inference of stochastic magneto-active dynamics and viscosity in Swift J1727.8-1613

Year: 2026

Type: article

Abstract: Linking X-ray variability to the underlying magnetohydrodynamic (MHD) dynamics of black hole X-ray binaries remains challenging. We systematically investigate the stochastic and oscillatory variability of the black hole X-ray binary candidate Swift J1727.8−1613 during its 2023 outburst using Gaussian process (GP) regression applied to Insight-HXMT multi-band light curves. The variability is modelled with a physically motivated composite kernel comprising one stochastically driven damped simple harmonic oscillator (SHO) and two damped random walk (DRW) components. The SHO term robustly recovers quasi-periodic oscillations (QPOs) with frequencies ν 0 ∼ 0.07–5 Hz, consistent with the fundamental Alfvén mode of a contracting magnetically confined disk–coronal cavity. The quality factor rises from Q ∼ 3 to Q ∼ 10, suggesting increasing coherence of the magnetic cavity. We also find an anti-correlation between QPO frequency and the short DRW damping timescale, supporting our proposed stochastic magneto-active dynamics scenario. We associate the short and long DRW timescales with the local turbulent turnover and thermal adjustment timescales, respectively. Under this proposed interpretation, our results are consistent with an effective viscosity parameter α ∼ 0.1. Strikingly, near the jet-ejection epoch around MJD 60206, the short DRW timescale is unresolved, while the long DRW timescale approaches the 0.1 s sampling limit, suggesting a rapid reorganisation of the disk internal energy balance immediately before jet launching. Our results establish GP inference as a powerful route to connecting X-ray timing observables with the dynamical state of black hole accretion flows.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202659872