Galactic cosmic rays (CRs) inside the heliosphere are affected by solar modulation. To investigate this phenomenon and its underlying physical mechanisms, we have performed a data-driven analysis of ...the temporal dependence of the CR proton flux over the solar cycle. The modulation effect was modeled by means of stochastic simulations of cosmic particles in the heliosphere. The model was constrained using measurements of CR protons made by AMS-02 and PAMELA experiments on a monthly basis from 2006 to 2017. With a global statistical analysis of these data, we have determined the key model parameters governing CR diffusion, its dependence on the particle rigidity, and its evolution over the solar cycle. Our results span over epochs of solar minimum and solar maximum, as well as epochs with magnetic reversal and opposite polarities. Along with the evolution of the CR transport parameters, we study their relationship with solar activity proxies and interplanetary parameters. We find that the rigidity dependence of the parallel mean free path of CR diffusion shows a remarkable time dependence, indicating a long-term variability in the interplanetary turbulence that interchanges across different regimes over the solar cycle. The evolution of the diffusion parameters shows a delayed correlation with solar activity proxies, reflecting the dynamics of the heliospheric plasma, and distinct dependencies for opposite states of magnetic polarity, reflecting the influence of charge-sign-dependent drift in the CR modulation.
Context. The secondary-to-primary boron-to-carbon (B/C) ratio is widely used to study the cosmic-ray (CR) propagation processes in the Galaxy. It is usually assumed that secondary nuclei such as ...Li-Be-B are generated entirely by collisions of heavier CR nuclei with the interstellar medium (ISM). Aims. We study the CR propagation under a scenario where secondary nuclei can also be produced or accelerated by Galactic sources. We consider the processes of hadronic interactions inside supernova remnants (SNRs) and the re-acceleration of background CRs in strong shocks. We investigate their impact in the propagation parameter determination within present and future data. Methods. Analytical calculations are performed in the frameworks of the diffusive shock acceleration theory and the diffusive halo model of CR transport. Statistical analyses are performed to determine the propagation parameters and their uncertainty bounds using existing data on the B/C ratio, as well as the simulated data expected from the AMS-02 experiment. Results. The spectra of Li-Be-B nuclei emitted from SNRs are harder than those due to CR collisions with the ISM. The secondary-to-primary ratios flatten significantly at ~TeV/n energies, both from spallation and re-acceleration in the sources. The two mechanisms are complementary to each other and depend on the properties of the local ISM around the expanding remnants. The secondary production in SNRs is significant for dense background media, n1 ≳ 1 cm-3, while the amount of re-accelerated CRs is relevant to SNRs expanding into rarefied media, n1 ≲ 0.1 cm-3. Owing to these effects, the diffusion parameter δ may be underestimated by a factor of ~5–15%. Our estimations indicate that an experiment of the AMS-02 caliber can constrain the key propagation parameters, while breaking the source-transport degeneracy for a wide class of B/C-consistent models. Conclusions. Given the precision of the data expected from ongoing experiments, the SNR production/acceleration of secondary nuclei should be considered, if any, to prevent a possible mis-determination of the CR transport parameters.
We report calculations of cosmic-ray proton, nuclei, antiproton, electron and positron energy spectra within a "two-halo model" of diffusive transport. The two halos represent a simple, physically ...consistent generalization of the standard diffusion models, which assume a unique type of diffusion for cosmic rays in the whole Galactic halo. We believe instead that cosmic rays may experience a smaller energy dependence of diffusion when they are in proximity of the Galactic disk. Our scenario is supported by recent observations of cosmic-ray protons, nuclei, anisotropy, and gamma-rays. We predict remarkably hard antiparticle spectra at high energy. In particular, at E>10 GeV, the antiproton/proton ratio is expected to flatten, while the positron fraction is found to increase with energy. We discuss the implications for cosmic-ray physics and dark matter searches via antimatter.
After six years of continuous observations in space, the Alpha Magnetic Spectrometer experiment has released new data on the temporal evolution of the proton and helium fluxes in cosmic rays. These ...data revealed that the ratio between proton and helium fluxes at the same value of rigidity R=p/Z (momentum/charge ratio) is not constant at R≲3 GV. In particular, the ratio is found to decrease steadily during the descending phase of Solar Cycle 24 toward the next minimum. We show that such a behavior is a remarkable signature of the β×λ(R) dependence in the diffusion of cosmic rays in heliosphere, where β is their adimensional speed and λ(R) is their mean free path, a universal function of rigidity for all nuclei. This dependence is responsible for distinctive charge or mass dependent effects in the time-dependent modulation of low-rigidity particles.
ABSTRACT Recent data on Galactic cosmic rays (CRs) revealed that the helium energy spectrum is harder than the proton spectrum. The AMS experiment has now reported that the proton-to-helium ratio as ...function of rigidity (momentum-to-charge ratio) falls off steadily as p/He with Δ = −0.08 between ∼ 40 GV and ∼ 2 TV. Besides, the single spectra of proton and helium are found to progressively harden at 100 GV. The p/He anomaly is generally ascribed to particle-dependent acceleration mechanisms occurring in Galactic CR sources. However, this explanation poses a challenge to the known mechanisms of particle acceleration since they are believed to be "universal," composition-blind rigidity mechanisms. Using the new AMS data, we show that the p/He anomaly can be simply explained in terms of a two-component scenario where the GeV-TeV flux is ascribed to a hydrogen-rich source, possibly a nearby supernova remnant, characterized by a soft acceleration spectrum. This simple idea provides a common interpretation for the p/He ratio and for the single spectra of proton and helium: both anomalies are explained by a flux transition between two components. The "universality" of particle acceleration in sources is not violated in this model. A distinctive signature of our scenario is the high-energy flattening of the p/He ratio at multi-TeV energies, which is hinted at by existing data and will be resolutely tested by new space experiments ISS-CREAM and CALET.
The Alpha Magnetic Spectrometer (AMS) experiment onboard the International Space Station (ISS) has recently measured the proton and helium spectra in cosmic rays (CRs) in the GeV-TeV energy region. ...The spectra of proton and helium are found to progressively harden at rigidity R=pc/Ze≳200 GV, while the proton-to-helium ratio as function of rigidity is found to fall off steadily as p/He∝R-0.08. The decrease of the p/He ratio is often interpreted in terms of particle-dependent acceleration, which is in contrast with the universal nature of diffusive-shock-acceleration mechanisms. A different explanation is that the p-He anomaly originates from a flux transition between two components: a sub-TeV flux component (L) provided by hydrogen-rich supernova remnants with soft acceleration spectra, and a multi-TeV component (G) injected by younger sources with amplified magnetic fields and hard spectra. In this scenario the universality of particle acceleration is not violated because both source components provide composition-blind injection spectra. The present work is aimed at testing the universality of CR acceleration using the low-energy part of the CR flux, which is expected to be dominated by the L-type component. However, at kinetic energy of ∼0.5–10GeV, the CR fluxes are significantly affected by energy losses and solar modulation, hence a proper modeling of Galactic and heliospheric propagation is required. To set the key properties of the L-source component, I have used the Voyager-1 data collected in the interstellar space. To compare my calculations with the AMS data, I have performed a determination of the force-field modulation parameter using neutron monitor measurements. I will show that the recent p-He data reported by AMS and Voyager-1 are in good agreement with the predictions of such a scenario, supporting the hypothesis that CRs are released in the Galaxy by universal, composition-blind accelerators. At energies below ∼0.5GeV/n, however, the model is found to underpredict the data collected by PAMELA from 2006 to 2010. This discrepancy is found to increase with increasing solar activity, reflecting an expected breakdown of the force-field approximation.
Penetrating particle ANalyzer (PAN) Wu, X.; Ambrosi, G.; Azzarello, P. ...
Advances in space research,
04/2019, Letnik:
63, Številka:
8
Journal Article
Recenzirano
Odprti dostop
PAN is a scientific instrument suitable for deep space and interplanetary missions. It can precisely measure and monitor the flux, composition, and direction of highly penetrating particles ...(>∼100 MeV/nucleon) in deep space, over at least one full solar cycle (11 years). The science program of PAN is multi- and cross-disciplinary, covering cosmic ray physics, solar physics, space weather and space travel. PAN will fill an observation gap of galactic cosmic rays in the GeV region, and provide precise information of the spectrum, composition and emission time of energetic particle originated from the Sun. The precise measurement and monitoring of the energetic particles is also a unique contribution to space weather studies. PAN will map the flux and composition of penetrating particles, which cannot be shielded effectively, precisely and continuously, providing valuable input for the assessment of the related health risk, and for the development of an adequate mitigation strategy. PAN has the potential to become a standard on-board instrument for deep space human travel.
PAN is based on the proven detection principle of a magnetic spectrometer, but with novel layout and detection concept. It will adopt advanced particle detection technologies and industrial processes optimized for deep space application. The device will require limited mass (20 kg) and power (20 W) budget. Dipole magnet sectors built from high field permanent magnet Halbach arrays, instrumented in a modular fashion with high resolution silicon strip detectors, allow to reach an energy resolution better than 10% for nuclei from H to Fe at 1 GeV/n. The charge of the particle, from 1 (proton) to 26 (Iron), can be determined by scintillating detectors and silicon strip detectors, with readout ASICs of large dynamic range. Silicon pixel detectors used in a low power setting will maintain the detection capabilities for even the strongest solar events. A fast scintillator with silicon photomultiplier (SiPM) readout will provide timing information to determine the entering direction of the particle, as well as a high rate particle counter. Low noise, low power and high density ASIC will be developed to satisfy the stringent requirement of the position resolution and the power consumption of the tracker.
A thorough understanding of solar effects on the galactic cosmic rays is relevant both to infer the local interstellar spectrum characteristics and to investigate the dynamics of charged particles in ...the heliosphere. We present a newly developed numerical modulation model to study the transport of galactic protons in the heliosphere. The model was applied to the 27-day averaged galactic proton flux recently released by the PAMELA and AMS02 experiments, covering an extended time period from mid-2006 to mid-2017.
The observed spectrum of Galactic cosmic rays has several exciting features such as the rise in thepositron fraction above ∼10 GeV of energy and the spectral hardening of protons and helium at≳300 ...GeV=nucleon of energy. The ATIC-2 experiment has recently reported an unexpected spectralupturn in the elemental ratios involving iron, such as the C=Fe or O=Fe ratios, at energy ≳50 GeV pernucleon. It is recognized that the observed positron excess can be explained by pion production processesduring diffusive shock acceleration of cosmic-ray hadrons in nearby sources. Recently, it was suggested thata scenario with nearby source dominating the GeV-TeV spectrum may be connected with the change of slopeobserved in protons and nuclei, which would be interpreted as a flux transition between the local componentand the large-scale distribution of Galactic sources. Here I show that, under a two-component scenario withnearby source, the shape of the spectral transition is expected to be slightly different for heavy nuclei, such asiron, because their propagation range is spatially limited by inelastic collisions with the interstellar matter.This enables a prediction for the primary/primary ratios between light and heavy nuclei. From this effect, aspectral upturn is predicted in the C=Fe and O=Fe ratios in good accordance with the ATIC-2 data.
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