Black Hole Observations from the Swamp: Simultaneous Optical/X-ray QPOs in MAXI J1820+070

We observed the black hole MAXI J1820+070 during its 2018 X-ray/optical outburst with a 14-inch telescope from the middle of Florida. Using our 1-Hz optical imaging, we find quasi-periodic oscillations (QPOs; which are related to jet activity) that increase exponentially in frequency over time, matching NuSTAR and NICER X-ray observations. While we were observing, we noticed that the optical flux of MAXI J1820+070 decoupled from its X-ray flux, but at the same time the optical QPO behavior did not change. This suggests that jet outflows generate a significant fraction of the optical light emission in this X-ray binary system. During this time, the optical color of MAXI J1820+070 changed from red to blue. Therefore the decoupling, which may be a disruption of the outer accretion disk, does not impact the QPO, which is related to the jet and located in the inner accretion disk. The decoupling shows the evolution of accretion during the outburst, presaging the black hole’s transition from a hard state to a soft state and then the fade-out of the outburst.