NICER observation list: Target ID 262501

We propose a short, optimized observing campaign of the super-Eddington neutron-star LMXB GX 5-1, to cover its entire Z track. Such coverage would allow us to study and compare the X-ray variability and spectral properties of the GX 5-1 in the context of the entire Z source ensemble. Our main goals are to study the emission mechanism of the low-frequency QPOs (for which GX 5-1 is a prime NICER target), through phase-resolved spectroscopy, and to investigate the properties of accretion discs at very high luminosities. We request a set of four 20 ks NICER observations, each separated by 1 day, an observing strategy that has proven to be very efficient for GX 5-1.