NICER observation list: Target ID 263501

We propose a series of 4 Target of Opportunity (ToO) observations with NuSTAR and NICER for any of the five following recurrent black hole binaries: GX 339-4, H1743-322, 4U 1630-47, XTE J1550-564, or XTE 1752-223. We aim to obtain high signal-to-noise spectra of these sources at different accretion states as they go into outburst. Our principal goal is to use X-ray reflection spectroscopy to track the evolution of the inner edge of the accretion disk as a function of luminosity; estimate the spin of the black hole; and measure the accretion disk inclination, density, ionization and iron abundance. These observations will provide crucial constraints to support a large-scale data analysis program for these sources.