On the spectrum of stable secondary nuclei in cosmic rays

Abstract

The ratio of the fluxes of secondary and primary nuclei in cosmic rays has long been used as an indicator of the grammage traversed in the journey of cosmic ray particles throughout the Galaxy. The basic idea is that primary particles are accelerated in astrophysical sources, such as supernova remnant shocks and eventually propagate in the Galactic volume, occasionally interacting with gas, mainly in the disc of the Galaxy, and there they produce secondary nuclei through spallation. At sufficiently high energy, typically $\gtrsim 100$ GeV/n, the ratio of fluxes of the secondary nucleus to that of the main primary nucleus is found to scale as $E_k^{-\delta }$, where $E_k$ is the energy per nucleon (a conserved quantity in spallation reactions) and $\delta$ identifies the energy dependence of the diffusion coefficient. The same shock waves that may be responsible for cosmic ray acceleration in the first place also pick up any other charged particle in the upstream, provided being above threshold for injection. The secondary nuclei produced by spallation in the interstellar medium are no exception, hence they also get accelerated. This effect is unavoidable, only its strength may be subject of debate. We compute the spectrum of secondary elements such as boron and lithium taking into account shock reacceleration and compare our predictions with the recent observations of the B/C ratio and preliminary measurements of the boron and lithium flux. Both these sets of data seem to confirm that reacceleration of secondary nuclei indeed plays an important role, thereby affecting the validity of those scaling rules that are often used in cosmic ray physics.

9 pages, 6 figures, Accepted for publication in MNRAS

References in corpus (13)

• Observation of an anomalous positron abundance in the cosmic radiation
• Discrepant hardening observed in cosmic-ray elemental spectra
• The origin of the positron excess in cosmic rays
• Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy
• Origin of the Cosmic Ray Spectral Hardening
• Measurement of boron and carbon fluxes in cosmic rays with the PAMELA experiment
• Testing astrophysical models for the PAMELA positron excess with cosmic ray nuclei
• Indications for a high-rigidity break in the cosmic-ray diffusion coefficient
• On the cosmic ray spectrum from type II Supernovae expanding in their red giant presupernova wind
• GeV-TeV cosmic-ray spectral anomaly as due to re-acceleration by weak shocks in the Galaxy
• Interpretation of the cosmic ray positron and antiproton fluxes
• Power requirements for cosmic ray propagation models involving diffusive reacceleration; estimates and implications for the damping of interstellar turbulence
• Cosmic-ray pressure driven magnetic field amplification: dimensional, radiative and field orientation effects

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• Indications for a high-rigidity break in the cosmic-ray diffusion coefficient
• Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory
• First Predicted Cosmic Ray Spectra, Primary-to-Secondary Ratios, and Ionization Rates from MHD Galaxy Formation Simulations
• The impact of astrophysical dust grains on the confinement of cosmic rays
• Effects of reacceleration and source grammage on secondary cosmic rays spectra
• Cosmic-Ray Lithium Production at the Nova Eruption Followed by a Type Ia Supernova
• The Important Role of Cosmic-Ray Re-Acceleration
• The Origin of the Very-High-Energy Diffuse $\gamma$-Ray Emission: The Case for Galactic Source Cocoons
• The population of Galactic supernova remnants in the TeV range
• Snowmass 2021 LoI: Determination of cosmic ray properties in the local interstellar medium with all-sky anisotropy observations