NICER observation list: Target ID 563001

A NICER timing campaign of 2019-2021 on the isolated neutron star RX J0806.4-4123 showed that its frequency derivative is unusually small. It is in fact so small that there still is the possibility for its positive as well as negative values despite the tight NICER constraints on the timing solution. The proposed additional observation will reduce the uncertainty of the frequency derivative by a factor of five. This can answer the question whether RX J0806.4-4123 spins down or up. The spin-up could be due to accretion from a fallback disk while a very slow spin-down would mean an unexpectedly low spin-down power of this isolated neutron star.