PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Cosmic-Ray Physics (Indirect, CRI)
Pitch-angle distribution of TeV cosmic rays in the local interstellar medium
M. Zhang*, N. Maalal and N. Pogorelov
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Pre-published on: August 17, 2023
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The electric and magnetic fields encountered by Galactic TeV cosmic rays (CRs) as they propagate deep into the heliosphere can alter their energy and arrival direction upon reaching Earth. This perturbation of trajectories in phase space can distort the angular distribution of particle flux, also known as anisotropy. The maps of TeV CR anisotropy obtained by air shower experiments appear quite complex. To remove heliospheric distrortions, we developed a theory of flux mapping based upon applying Liouville's theorem to the CR trajectories obtained via a multi-fluid magnetohydrodynamic model of the heliosphere. With this technique, we determined the original CR distribution function in the pristine local interstellar medium. In this paper, we focus on the dependence of TeV CR intensity on the particle pitch-angle relative to the direction of the local interstellar magnetic field. The pitch-angle distribution has two significant features: it is dominated by a dipole anisotropy, and it displays a notable increase in particle intensity towards the direction aligning with the magnetic field at the zero pitch angle. The dipole anisotropy suggests that TeV CRs are scattered nearly isotropically by the interstellar magnetic field turbulence instead of expected behavior resulting from resonant scattering by turbulence with a Kolmogorov power spectrum. The increase of particles towards zero pitch-angle implies particle focusing by an inhomogeneous interstellar magnetic field with a gradient length approximately equal to 6 times the CR mean free path.
DOI: https://doi.org/10.22323/1.444.0328
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