NICER observation list: Target ID 762601

X-ray reflection in accreting black holes probes the inner region of the accretion disc, and proper modelling of the spectral and timing properties of this emission enables measurement of the black hole mass and spin. The unique combination of NICER s soft and NuSTAR's hard coverage provides the broad bandpass, high count rates and energy and timing resolution required to constrain models of the time-averaged energy spectrum and the reverberation lag energy spectrum on different timescales. We propose to observe any black hole transient, known or unknown, exceeding 50 mCrab during the bright hard state for 50 ks with simultaneous NICER and NuSTAR observation in order to access unprecedented characterization of black hole spin and mass.