An Analysis of the North Polar Spur Using HaloSat

• Published in: The Astrophysical journal 2020-11, Vol.904 (1), p.54
• Main Authors: LaRocca, Daniel M., Kaaret, Philip, Kuntz, K. D., Hodges-Kluck, Edmund, Zajczyk, Anna, Bluem, Jesse, Ringuette, Rebecca, Jahoda, Keith M.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; Diffuse x-ray background; Electron density; Emission measurements; Field of view; Interstellar medium; Ionization; Magnetic fields; North Polar Spur (astronomy); Superbubbles; Temperature gradients; X-ray astronomy
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/abbdfd

We present HaloSat X-ray observations of the entirety of the bright X-ray emitting feature known as the North Polar Spur (NPS). The large field of view of HaloSat enabled coverage of the entire bright NPS in only 14 fields, which were each observed for 30,000 s. We find that the NPS fields are distinct in both brightness and spectral shape from the surrounding halo fields. We fit the NPS as two thermal components in ionization equilibrium with temperatures and . We note a temperature gradient in the NPS hot component with an inner arc temperature warmer than the outer arc. The emission measures we find for the cool component of the NPS is a factor of 3-5 greater than that of the hot component, which suggests that the bulk of the NPS material is in the 0.1 keV component. We evaluate distance estimates of 0.4 and 8.0 kpc for the NPS. Our findings suggest a preference for a distant NPS with an energy of 6 × 1054 erg, an age of 10 Myr, and pressures consistent with a 10 G magnetic field associated with the Fermi bubbles. The electron density 10 × 10−3 cm−3 is consistent with estimates for the shock region surrounding a Galactic-scale event.