Measuring the Jet-Black Hole Spin Misalignment in MAXI J1820+070

Compact relativistic jets are commonly observed across multiple wavelengths during the hard-state outbursts of black hole X-ray binaries. If the axis of the jet is misaligned with the black hole spin, the jet will precess due to the effect of frame dragging of the spinning black hole. In this work, we present the first measurement of this jet-spin misalignment by modeling the phase-resolved spectra of X-ray quasi-periodic oscillations (QPOs) detected in MAXI J1820+070 during its hard state. We find the misalignment angle to be $30.3\degree_{-3.1\degree}^{+3.2\degree}$, demonstrating significant evolution throughout the hard state, with the statistical significance much greater than $5\sigma$. This result supports a geometric origin for QPOs within the black hole spacetime and provides direct observational evidence that the low-frequency QPOs (LFQPOs) in MAXI J1820+070 arise from jet precession. The measured misalignment angle substantially exceeds the jet opening angle, suggesting that jet material undergoes stronger outward acceleration than predicted by current models.