NICER observation list: Target ID 254103

Over the past few years, very successful campaigns on several Galactic black hole (BH) X-ray binaries have revealed tantalising sub-second variations 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? We propose anticipated ToO observations of up to 2 hard state outbursts with NICER, strictly simultaneous with ground-based 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, create spectral energy distributions, and probe these systems on theory-critical, unprecedented scales.