NICER observation list: Target ID 661103

We propose to observe for the first time the transition from the accretion state to the 'propeller' regime in 'real time'. At this point the interaction of the accretion flow with magnetic field of an X-ray pulsar (XRP) is known to abruptly inhibit the accretion, however, the transition itself has not been observed up to now. As a target we propose one of the transient XRP 4U 0115+63 and V 0332+53 which had already been observed in both states, and where the time of the transition can be predicted accurately. These two objects provide thus a unique opportunity for a first detailed study of plasma interaction with the magnetic field of the NS, The unique combination of spectral and timing capabilities with great flexibility make NICER the only instrument capable of such observation.