Are low-frequency QPOs caused by Lense-Thirring precession?
In plain words
The X-ray brightness of accreting black holes wobbles with a near-regular period of 0.03 to 10 s (a quasi-periodic oscillation, QPO), possibly because frame dragging by the spinning hole makes the inner gas flow precess like a tilted top.
Precise statement
Type-C QPOs at 0.1 to 30 Hz appear in hard and intermediate states of black-hole X-ray binaries. Determine whether they arise from Lense-Thirring precession of a hot inner flow inside the disk truncation radius or from disk instabilities (accretion-ejection instability, oscillation modes), using QPO-phase-resolved iron-line centroid modulation, inclination dependence of QPO amplitude and phase lags, and QPO-phase-resolved X-ray polarization. Answer: yes or no for precession, with the evidence.
What would settle it
QPO-phase-resolved X-ray polarimetry and iron-line spectroscopy in several sources showing or excluding the modulation pattern predicted by precession.
Status in the literature
2016: QPO-phase-resolved spectroscopy of H1743-322 found the iron-line centroid energy modulated with QPO phase, as precession predicts; instability models are not excluded.