X-ray spectra of z sources

A physically consistent model has been proposed that seeks to explain in a unified way the X-ray spectra and rapid variability of the Z sources and other weakly magnetic neutron stars in low-mass systems. Here we describe a simple, four-parameter spectral model derived from the unified model that accurately reproduces the X-ray colors, spectra, and count rates of the Z sources. in this model, photons are produced primarily by electron cyclotron emission in the neutron star magnetosphere and are then Comptonized in the magnetosphere, hot central corona, and inward radial flow. In addition to explaining their Z tracks, the model explains several other previously unexplained properties of the Z sources.