Cosmic-ray electrons and the magnetic field of the North Polar Spur

Abstract

The recent confirmation of the bipolarity of the eROSITA bubbles suggests that the well-known North Polar Spur (NPS)/Loop I probably is a 10 kpc sized relic in the Galactic halo and not a small local structure near the Sun. By virtue of multiwavelength observations of the NPS, unprecedentedly precise parameter constraints on the cosmic-ray electrons (CRes) and magnetic field in the post-shock halo medium can be provided. The parameters of the CRes and the magnetic field can be derived independently by modeling the gamma-ray and the radio data of the NPS via inverse Compton scattering and synchrotron emission, respectively. Our main results are (1) that the energy density of the CRe is (3-6)$\times 10^{-14}$ erg cm${}^{-3}$, and the spectral index is $p\simeq 2.0\pm 0.1,$ below the cooling break energy of about 5 GeV; (2) that the magnetic field strength is 3 $\mu$G; and (3) that the shock acceleration efficiency of the CRe is (1-2)%. Given the Mach number of 1.5, the high acceleration efficiency and flat spectrum of the CRe suggest that preexisting relativistic electrons may be reaccelerated in the NPS. Alternatively, these CRes could be accelerated by an evolving shock in the early epoch when its Mach number is high, and efficiently diffuse throughout the post-shock halo gas. In addition, the cooling break energy suggests that the cooling timescale is $10^7$ yr, which agrees with the age of the eROSITA bubbles.

Accepted for publication in A&A Letters

References in corpus (21)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• Diffuse Radio Emission from Galaxy Clusters
• The Spectrum and Morphology of the Fermi Bubbles
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• Detection of large-scale X-ray bubbles in the Milky Way halo
• Giant Magnetized Outflows from the Centre of the Milky Way
• Separation of anomalous and synchrotron emissions using WMAP polarization data
• Inverse Compton Emission from Galactic Supernova Remnants: Effect of the Interstellar Radiation Field
• A New Model For The Loop-I (The North Polar Spur) Region
• All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz
• Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*
• Polarised radio filaments outside the Galactic plane
• Nuclear Outflow of the Milky Way: Studying the Kinematics and Spatial Extent of the Northern Fermi Bubble
• Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?
• The North Polar Spur and Aquila Rift
• Revisiting the distance to radio Loops I and IV using Gaia and radio/optical polarization data
• Constraining the Distance to the North Polar Spur with Gaia DR2
• Asymmetric eROSITA bubbles as the evidence of a circumgalactic medium wind
• Diagnostics of Gaseous Halo of the Milky Way by a Shock Wave from the Galactic Centre
• Signatures of Recent Cosmic-Ray Acceleration in the High-Latitude $\gamma$-Ray Sky

Cited by in corpus (1)

• Sources and Radiations of the Fermi Bubbles