NICER observation list: Target ID 651107

Over the past few years, successful multiwavelength campaigns on a handful of Galactic Black Hole (BH) X-ray Binaries have revealed remarkable sub-second variability and significant optical/infrared-vs-X-ray correlations, with some arising in the first acceleration zone at the base of a compact, relativistic jet. But what drives these variations, and are they really as stable as they sometimes appear? Here we propose up to 10 individual anticipated ToO observations (5ks each) on 1--2 hard state outbursts, strictly simultaneous with optical/infrared timing. We will probe rapid, sub-second photometric variations and search for inter-band time delays to disentangle the jet/disc/coronal components using spectral-timing, and probe these systems on theory-critical, unprecedented scales.