NICER observation list: Target ID 865601

We propose a month-long NICER monitoring campaign of Cygnus X-1, using 120 1ks exposures, simultaneous with optical monitoring of the source. This will not only allow us to probe the connection between the optical and X-ray variability in detail, but also establish an unprecedented data set, which will help advance our understanding of the physics of accretion. Through this program, we aim to identify the correlation and lag between the optical flaring of the companion star that fuels the accretion onto the black hole, the presence and strength of X-ray absorption features caused by stellar winds, and the changes in X-ray flux of the inner regions of the accretion disk. This project will explain the way black holes in high-mass X-ray binaries are fed by their stellar companion.