In this thesis, we aim at studying some of the open questions regarding the origin of the "Cosmic Rays" (CRs), as well as their transport properties. The exceptional quality of the experimentally measured cosmic-ray observables, especially at the recently-achieved energies in the range ~O(100 GeV - 1 TeV), started to question the standard picture, based on a "Supernova Remnant"-(SNR)-only origin of the CRs and a diffusive propagation inspired by the "Quasi-Linear Theory" (QLT) of pitch-angle interaction against alfvénic turbulence. First, we reproduce the most relevant cosmic-ray observables to tune the propagation setup, numerically solving the transport equation with the DRAGON code. On top of this, to account for the rising of the e^+ above ~10 GeV, we fit a primary population of positrons originating in Pulsar Wind Nebulae, in a model-independent setup that considers the uncertainties in the pulsar injections mechanism. Since the all-lepton spectrum is still not reproduced above ~50 GeV --- and in particular the ~TeV break --- we consider the contribution from a nearby source of e^-, and conclude that an old t_{age} ~ 10^5 yr SNR, located between ~600 pc and ~1 kpc, is probably missing from the Catalogues. Within the hypothesis of such old remnant in its radiative phase contributing to the e^+ + e^-, we search for its signature in the proton flux as well. To do this, we consider a phenomenological propagation setup that reproduces the hadronic spectral hardening at ~200 GeV as a diffusive feature D(E) ~ E^delta(E), and adopt it consistently for the large-scale background and for the nearby source. Within this framework, we account for the all-lepton spectrum, the proton spectrum and the cosmic-ray dipole anisotropy with the same old (t_{age} = 2*10^5 yr), nearby (d = 300 pc) remnant. We highlight that the progressively hardening diffusion coefficient is a crucial ingredient, since, in a single-power-law diffusion scenario, the dipole anisotropy data would be overshot by, at least, one order of magnitude. Finally, we explore the phenomenological implications of a change of paradigm in the standard cosmic-ray diffusion --- based on wave-particle interaction with Alfvén fluctuations --- considering a non-linear extension of the QLT that enhances the efficiency of CR-scattering with the other "Magneto-Hydro-Dynamic" (MHD) modes. Indeed, assuming the anisotropy of the alfvénic cascade, its scattering rate at all energies below ~100 TeV is not able to confine charged cosmic rays, and the fast magnetosonic modes alone shape the diffusion coefficient that particles experience in the Galaxy. Within such picture, we implement the resulting D(E) in DRAGON2, where two independent zones differently affect the evolution of the MHD cascade: the Halo (L_{Halo} ~ 5-6 kpc) and the Warm Ionized Medium (L_{WIM} ~ 1 kpc). We find that, with a reasonable choice of selected quantities, representing the physics of the environments, we can reproduce the hadronic fluxes, as well as the boron-over-carbon ratio, from ~200 GeV above. We assign to the rising of the "streaming instabilities" the cosmic-ray transport below this energy.

Fornieri, O. (2021). Cosmic-ray transport in the Milky Way and related phenomenology [10.25434/fornieri-ottavio_phd2021].

Cosmic-ray transport in the Milky Way and related phenomenology

Fornieri, Ottavio
2021-01-01

Abstract

In this thesis, we aim at studying some of the open questions regarding the origin of the "Cosmic Rays" (CRs), as well as their transport properties. The exceptional quality of the experimentally measured cosmic-ray observables, especially at the recently-achieved energies in the range ~O(100 GeV - 1 TeV), started to question the standard picture, based on a "Supernova Remnant"-(SNR)-only origin of the CRs and a diffusive propagation inspired by the "Quasi-Linear Theory" (QLT) of pitch-angle interaction against alfvénic turbulence. First, we reproduce the most relevant cosmic-ray observables to tune the propagation setup, numerically solving the transport equation with the DRAGON code. On top of this, to account for the rising of the e^+ above ~10 GeV, we fit a primary population of positrons originating in Pulsar Wind Nebulae, in a model-independent setup that considers the uncertainties in the pulsar injections mechanism. Since the all-lepton spectrum is still not reproduced above ~50 GeV --- and in particular the ~TeV break --- we consider the contribution from a nearby source of e^-, and conclude that an old t_{age} ~ 10^5 yr SNR, located between ~600 pc and ~1 kpc, is probably missing from the Catalogues. Within the hypothesis of such old remnant in its radiative phase contributing to the e^+ + e^-, we search for its signature in the proton flux as well. To do this, we consider a phenomenological propagation setup that reproduces the hadronic spectral hardening at ~200 GeV as a diffusive feature D(E) ~ E^delta(E), and adopt it consistently for the large-scale background and for the nearby source. Within this framework, we account for the all-lepton spectrum, the proton spectrum and the cosmic-ray dipole anisotropy with the same old (t_{age} = 2*10^5 yr), nearby (d = 300 pc) remnant. We highlight that the progressively hardening diffusion coefficient is a crucial ingredient, since, in a single-power-law diffusion scenario, the dipole anisotropy data would be overshot by, at least, one order of magnitude. Finally, we explore the phenomenological implications of a change of paradigm in the standard cosmic-ray diffusion --- based on wave-particle interaction with Alfvén fluctuations --- considering a non-linear extension of the QLT that enhances the efficiency of CR-scattering with the other "Magneto-Hydro-Dynamic" (MHD) modes. Indeed, assuming the anisotropy of the alfvénic cascade, its scattering rate at all energies below ~100 TeV is not able to confine charged cosmic rays, and the fast magnetosonic modes alone shape the diffusion coefficient that particles experience in the Galaxy. Within such picture, we implement the resulting D(E) in DRAGON2, where two independent zones differently affect the evolution of the MHD cascade: the Halo (L_{Halo} ~ 5-6 kpc) and the Warm Ionized Medium (L_{WIM} ~ 1 kpc). We find that, with a reasonable choice of selected quantities, representing the physics of the environments, we can reproduce the hadronic fluxes, as well as the boron-over-carbon ratio, from ~200 GeV above. We assign to the rising of the "streaming instabilities" the cosmic-ray transport below this energy.
2021
Gaggero, Daniele
Muñoz, Carlos
Fornieri, O. (2021). Cosmic-ray transport in the Milky Way and related phenomenology [10.25434/fornieri-ottavio_phd2021].
Fornieri, Ottavio
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11365/1143115