NICER observation list: Target ID 464201

Fast X-ray variability, e.g. quasi-periodic oscillations (QPOs), is a distinct characteristic of black hole low-mass X-ray binaries. Fast transitions between different types of QPOs or broadband noise are sometimes observed with significant spectral changes. The study of the fast transitions can provide important evidence on what triggers a QPO and on the physical origin of the QPO, which help us better understand the mechanism responsible for the state transitions. NICER s superb time resolution and large effective area below 2 keV make it an ideal mission to study the fast transitions, especially on how the disk changes during the transitions. In this proposal, we ask for 120 ks NICER observations of next black hole candidate showing fast transitions to fully probe the spectral changes.