NICER observation list: Target ID 566101

4U 1626-67 is an unusual low-mass ultracompact X-ray binary with a ~42 minute orbital period which hosts a ~7.7 s pulsar with a strong magnetic field of B ~ 3e12 G. It has exhibited two episodes of torque reversals in 1990 and 2008, and it is currently in the sustained spin-up state. We propose a 40 ks observation, quasi-simultaneous with the Imaging X-ray Polarimetry Explorer (IXPE), slated for launch on 12/09/2021. Joint NICER and IXPE observations will provide us with a level of unprecedented synergy that will enable accurate spectropolarimetric analysis designed to constrain the emission region geometry, to discern the distinct behavior between the spin-up and spin-down states, and to understand the flaring behavior that occurs only in the spin-up state.