Revisiting the Spatially Dependent Propagation Model with the Latest Observations of Cosmic-Ray Nuclei

Liu, Wei; Yao, Yixu; Guo, Yi-Qing

doi:10.3847/1538-4357/aaef39

Cited by 56 publications

(62 citation statements)

References 61 publications

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“…Blasi & Amato 2012b), again almost exclusively with "constant diffusivity" models (although a few studies have considered models where κ varies with e.g. galacto-centric radius in some idealized fashion; see Liu et al 2018). As we noted above and in Papers I & II, our favored values of κ and the scalings in e.g.…”

Section: Comparison To Other Cosmological Simulations and Previous Workmentioning

confidence: 99%

Testing physical models for cosmic ray transport coefficients on galactic scales: self-confinement and extrinsic turbulence at ∼GeV energies

Hopkins

Squire

Chan

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The microphysics of ∼ GeV cosmic ray (CR) transport on galactic scales remain deeply uncertain, with almost all studies adopting simple prescriptions (e.g. constant-diffusivity). We explore different physically-motivated, anisotropic, dynamical CR transport scalings in high-resolution cosmological FIRE simulations of dwarf and ∼L* galaxies where scattering rates vary with local plasma properties motivated by extrinsic turbulence (ET) or self-confinement (SC) scenarios, with varying assumptions about e.g. turbulent power spectra on un-resolved scales, Alfvén-wave damping, etc. We self-consistently predict observables including γ-rays (Lγ), grammage, residence times, and CR energy densities to constrain the models. We demonstrate many non-linear dynamical effects (not captured in simpler models) tend to enhance confinement. For example, in multi-phase media, even allowing arbitrary fast transport in neutral gas does not substantially reduce CR residence times (or Lγ), as transport is rate-limited by the ionized WIM and “inner CGM” gaseous halo (104 − 106 K gas within ≲ 10 − 30 kpc), and Lγ can be dominated by trapping in small “patches.” Most physical ET models contribute negligible scattering of ∼1 − 10 GeV CRs, but it is crucial to account for anisotropy and damping (especially of fast modes) or else scattering rates would violate observations. We show that the most widely-assumed scalings for SC models produce excessive confinement by factors ≳ 100 in the WIM and inner CGM, where turbulent and Landau damping dominate. This suggests either a breakdown of quasi-linear theory used to derive the CR transport parameters in SC, or that other novel damping mechanisms dominate in intermediate-density ionized gas.

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Section: Comparison To Other Cosmological Simulations and Previous Workmentioning

confidence: 99%

Testing physical models for cosmic ray transport coefficients on galactic scales: self-confinement and extrinsic turbulence at ∼GeV energies

Hopkins

Squire

Chan

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The diffusion parameters in the inner and outer halo are connected smoothly [19]. The parameterized diffusion coefficient adopted in this work is [19,36]…”

Section: Spatially-dependent Diffusionmentioning

confidence: 99%

“…The corresponding transport parameters are given in Table 1. The GCR secondary-to-primary ratios can be reasonably reproduced with these parameters [36]. The injection spectrum of background sources is assumed to be an exponential cutoff power-law form of rigidity,…”

Section: Spatially-dependent Diffusionmentioning

confidence: 99%

Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies

Liu

Guo

Yuan

2019

J. Cosmol. Astropart. Phys.

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The origin of Galactic cosmic rays (GCRs) remains a mystery after more than one century of their discovery. The diffusive propagation of charged particles in the turbulent Galactic magnetic field makes us unable to trace back to their acceleration sites. Nevertheless, nearby GCR source(s) may leave imprints on the locally measured energy spectra and the anisotropies of the arrival direction. In this work we propose a simple but natural description of the GCR production and propagation, within a two-zone disk-halo diffusion scenario together with a nearby source, to understand the up-to-date precise measurements of the energy spectra and anisotropies of GCRs. We find that a common energy scale of ∼ 100 TeV appears in both energy spectra of protons and helium nuclei measured recently by CREAM and large-scale anisotropies detected by various experiments. These results indicate that one or more local sources are very likely important

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“…In the outer halo (|z| > ξz h ), particles diffuse much faster. The parameterized diffusion coefficient we adopt is [62,63]…”

Section: Spatially-dependent Diffusionmentioning

confidence: 99%

Anisotropies of different mass compositions of cosmic rays

Qiao

Liu

Guo

et al. 2019

J. Cosmol. Astropart. Phys.

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The spectral hardenings of cosmic ray nuclei above ∼ 200 GV followed by softenings around 10 TV, the knee of the all-particle spectrum around PeV energies, as well as the pattern change of the amplitude and phase of the large-scale anisotropies around 100 TeV indicate the complexities of the origin and transportation of Galactic cosmic rays. It has been shown that nearby source(s) are most likely to be the cause of such spectral features of both the spectra and the anisotropies. In this work, we study the anisotropy features of different mass composition (or mass groups) of cosmic rays in this nearby source model. We show that even if the spectral features from the nearby source component is less distinctive compared with the background component from e.g., the population of distant sources, the anisotropy features are more remarkable to be identified. Measurements of the anisotropies of each mass composition (group) of cosmic rays by the space experiments such as DAMPE and HERD and the ground-based experiments such as LHAASO in the near future are expected to be able to critically test this scenario.

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Revisiting the Spatially Dependent Propagation Model with the Latest Observations of Cosmic-Ray Nuclei

Cited by 56 publications

References 61 publications

Testing physical models for cosmic ray transport coefficients on galactic scales: self-confinement and extrinsic turbulence at ∼GeV energies

Testing physical models for cosmic ray transport coefficients on galactic scales: self-confinement and extrinsic turbulence at ∼GeV energies

Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies

Anisotropies of different mass compositions of cosmic rays

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