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The North Polar Spur (NPS) is a giant structure that is clearly visible inboth radio and X-ray all-sky maps. We analyzed broadband radio observationscovering a range between 22 MHz and 70 GHz to systematically analyze thethermal/non-thermal emissions associated with the NPS. We demonstrate that theradio emission of the NPS comprises synchrotron, free-free, and dust emission;however, synchrotron emissions dominate over other emissions, especially athigh galactic-latitudes. Moreover, the synchrotron spectra exhibit a power-lawbehavior with $N(\gamma)\propto\gamma^{-s}$ ($s\simeq1.8-2.4$) up to a few GHzmoderated by a turnover at $\nu_{\rm brk} \simeq 1$ GHz, above which thespectral index $s$ decrease by one. Assuming that the turnover is due to theelectrons cooled by synchrotron radiation before escaping (or advecting) fromthe emission region, the magnetic field strength can be estimated to be $B\sim8 \rm\mu G$ if the NPS is a distant structure that is near the Galactic Center(GC). However, an unreasonably strong $B\sim 114\rm\mu G$ is required if theNPS is near the local supernova remnant (SNR). The corresponding non-thermalenergy stored in the NPS is $E_{\rm n/th}\simeq 4.4\times 10^{55}$ erg in theGC scenario, whereas $E_{\rm n/th}\simeq 4.1\times 10^{52}$ erg is difficult toexplain with a single local SNR. We also estimated the gamma-ray emissionassociated with the NPS through inverse Comptonization of the cosmic microwavebackground (CMB), which peaks at 100 - 1000 keV with a flux of $\nu F_{\nu}\sim10^{-9}$ $\rm erg\,cm^{-2}s^{-1}sr^{-1}$ in the GC model, and may be a goodcandidate for detection by future X-ray/gamma-ray observatories.

Broadband radio study of the North Polar Spur: Origin of the spectral turnover with insights into the X-ray and Gamma-ray spectra