A new look at the north Polar Spur

Abstract

The North Polar Spur (NPS) seems to consist of distinct shells. On the outside there is the H I shell (the H I NPS) and interior to this is the radio continuum shell (the RC NPS), which contains ionized gas. A region of doffise X-ray enhancement is found inside the RC NPS. From derived values of Faraday depolarization of the radio continuum emission, in conjunction with upper limits on the H..cap alpha.. line intensity, we find that in the RC NPS, the parallel component of the magnetic field B(par)> or =1.2 ..mu..gauss, and the electron density n(e)< or =0.4 cm/sup -3/. From an attempt to observe Zeeman splitting of the 21 cm line we find that B(par)< or =6 ..mu..gauss in the H I NPS. We use these results to present a self-consistent discussion of the region as being the result of a spherical shock which occurred long ago and is no longer expanding.