2007ApJ...664..349W

The North Polar Spur (NPS) is the brightest filament of Loop I, a large circular feature in the radio continuum sky. In this paper, a model consisting of two synchrotron-emitting shells is presented that reproduces large-scale structures revealed by recent polarization surveys. The polarized emission of the NPS is reproduced by one of these shells. The other shell, which passes close to the Sun, gives rise to polarized emission toward the Galactic poles. It is proposed that X-ray emission seen toward the NPS is produced by the interaction of the two shells. Two OB associations coincide with the centers of the shells. A formation scenario of the Loop I region is suggested.