A new analytical model of the cosmic-ray energy flux for Galactic diffuse radio emission

Abstract

Low-frequency radio observations of diffuse synchrotron radiation offer a unique vantage point for investigating the intricate relationship between gas and magnetic fields in the formation of structures within the Galaxy, spanning from the diffuse interstellar medium (ISM) to star-forming regions. Achieving this pivotal objective hinges on a comprehensive understanding of cosmic-ray properties, which dictate the effective energy distribution of relativistic electrons, primarily responsible for the observable synchrotron radiation. Notably, cosmic-ray electrons (CRe) with energies between 100 MeV and 10 GeV play a crucial role in determining the majority of the sky brightness below the GHz range. However, their energy flux ($j_e$) remains elusive due to solar modulation. We propose deriving observational constraints on this energy gap of interstellar CRe through the brightness temperature spectral index of low-frequency radio emission, here denoted as ${\beta }_{\mathrm{obs}}$. We introduce a new parametric analytical model that fits available data of $j_e$ in accordance with the ${\beta }_{\mathrm{obs}}$ values measured in the literature between 50 MHz to 1 GHz for diffuse emission in the Milky Way. Our model allows to account for multiple observations considering magnetic-field strengths consistent with existing measurements below 10 $\mu$G. We present a first all-sky map of the average component of the magnetic field perpendicular to the line of sight and validate our methodology against state-of-the art numerical simulations of the diffuse ISM. This research makes headway in modeling Galactic diffuse emission with a practical parametric form. It provides essential insights in preparation for the imminent arrival of the Square Kilometre Array.

7 pages, 6 figures, accepted for publication by A&A

References in corpus (26)

• Array Programming with NumPy
• A High Order Godunov Scheme with Constrained Transport and Adaptive Mesh Refinement for Astrophysical MHD
• Radio observational constraints on Galactic 3D-emission models
• All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz
• Toward Empirical Constraints on the Global Redshifted 21 cm Brightness Temperature During the Epoch of Reionization
• Simulating polarized Galactic synchrotron emission at all frequencies, the Hammurabi code
• Low-frequency Faraday rotation measures towards pulsars using LOFAR: probing the 3-D Galactic halo magnetic field
• Polarised radio filaments outside the Galactic plane
• Faraday tomography of the local interstellar medium with LOFAR: Galactic foregrounds towards IC342
• Improved Measurement of the Spectral Index of the Diffuse Radio Background Between 90 and 190 MHz
• Spectral Index of the Diffuse Radio Background Between 50 and 100 MHz
• The correct sense of Faraday rotation
• Low energy cosmic rays
• 3D chemical structure of diffuse turbulent ISM. I. Statistics of the HI-to-H${}_2$ transition
• Diffuse polarized emission in the LOFAR Two-meter Sky Survey
• The North Polar Spur and Aquila Rift
• Spectral index of the Galactic foreground emission in the 50-87 MHz range
• Spectral index of synchrotron emission: insights from the diffuse and magnetised interstellar medium
• The multiphase and magnetized neutral hydrogen seen by LOFAR
• Synchrotron Emission on FIRE: Equipartition Estimators of Magnetic Fields in Simulated Galaxies with Spectrally-Resolved Cosmic Rays
• Where Did the Amaterasu Particle Come From?
• Origin of Galactic Spurs: New Insight from Radio/X-ray All-sky Maps
• First look at the multiphase interstellar medium with synthetic observations of low-frequency Faraday tomography
• Cosmic-ray electrons released by supernova remnants
• Free-free absorption parameters of Cassiopeia A from low-frequency interferometric observations
• The Orion-Taurus ridge: a synchrotron radio loop at the edge of the Orion-Eridanus superbubble

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