NICER observation list: Target ID 570101

We propose a joint 50 ks NuSTAR and 5 ks NICER TOO observation of a transient black hole (BH) X-ray binary source during outburst. Using NICER monitoring to determine the source state, we will trigger the primary joint NuSTAR/NICER observation when the source transitions from the hard state to its intermediate state. Modeling reflection features in the source spectrum will be used to measure the BH spin, as well as constrain the innermost environment of the accretion disk. We will only target sources that have not yet been observed by NuSTAR during outburst, whether that means an entirely new transient BH candidate or a previously known BH X-ray binary that has been in quiescence since the launch of NuSTAR. Examples of well-known sources include GRO J1655-40 and XTE J1550-564.