NICER observation list: Target ID 770501

Z sources are some of the most enigmatic persistent sources in the X-ray sky. We propose observations of the Z source GX 340+0 with IXPE and NICER for total exposures of 300 ks and 12 ks, respectively. The main goal of this program is to constrain the accretion geometry, in particular, that of the thermal component and the corona, by measuring the energy dependent polarization. By comparing our results with spectro-polarimetric modeling of other Z sources, we aim to develop a more robust picture of the complex accretion flows in these systems. GX 340+0 traces all the spectral states along its Z-track on a time scale of a few days; with our proposed observations we will likely sample a full Z track with IXPE for the first time.