HFQPOs and discoseismic mode excitation in eccentric, relativistic discs. II. Magnetohydrodynamic simulations

Abstract

Trapped inertial oscillations (r-modes) provide a promising explanation for high-frequency quasi-periodic oscillations (HFQPOs) observed in the emission from black hole X-ray binary systems. An eccentricity (or warp) can excite r-modes to large amplitudes, but concurrently the oscillations are likely damped by magnetohydrodynamic (MHD) turbulence driven by the magnetorotational instability (MRI). We force eccentricity in global, unstratified, zero-net flux MHD simulations of relativistic accretion discs, and find that a sufficiently strong disc distortion generates trapped inertial waves despite this damping. In our simulations, eccentricities above ∼ 0.03 in the inner disc excite trapped waves. In addition to the competition between r-mode damping and driving, we observe that larger amplitude eccentric structures modify and in some cases suppress MRI turbulence. Given the variety of distortions (warps as well as eccentricities) capable of amplifying r-modes, the robustness of trapped inertial wave excitation in the face of MRI turbulence in our simulations provides support for a discoseismic explanation for HFQPOs.

Dynamical structure of highly eccentric discs with applications to tidal disruption events

“…However recent work has demonstrated the thermal instability in radiation dominated MHD discs (Latter & Papaloizou 2012;Jiang et al 2013;Mishra et al 2016;Ross et al 2017). How well this translates into an eccentric disc is highly uncertain as there have been very few studies of MRI in eccentric discs (Chan et al (2018); Dewberry et al (2020) being notable exceptions).…”

Confrontation of Observation and Theory: High Frequency QPOs in X-ray Binaries, Tidal Disruption Events, and Active Galactic Nuclei

“…This model garners further plausibility from the fact that it, alone among the diskoseismic modes, has been unambiguously detected in a hydrodynamic disk simulation ; however, we note that in this study, the QPO disappeared when a magnetic field was included, due to turbulence induced by the magneto-rotational instability. Very recent work by Dewberry et al (2020) presents a more optimistic picture: when eccentricity or warping is forced in relativistic magnetohydrodynamic simulations, the coupling of the trapped g-and p-modes to the distortion amplifies the modes even in the presence of MHD turbulence.…”