We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE air FD is also sensitive to the Cherenkov ...light produced by shower particles. Low-energy cosmic rays, in the PeV energy range, are detectable by TALE as Cherenkov events. Using these events, we measure the energy spectrum from a low energy of ∼2 PeV to an energy greater than 100 PeV. Above 100 PeV, TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than a few EeV. In this paper, we describe the detector, explain the technique, and present results from a measurement of the spectrum using ∼1000 hr of observation. The observed spectrum shows a clear steepening near 1017.1 eV, along with an ankle-like structure at 1016.2 eV. These features present important constraints on the origin of galactic cosmic rays and on propagation models. The feature at 1017.1 eV may also mark the end of the galactic cosmic ray flux and the start of the transition to extragalactic sources.
The Alpha Magnetic Spectrometer (AMS) is a precision particle physics detector on the International Space Station (ISS) conducting a unique, long-duration mission of fundamental physics research in ...space. The physics objectives include the precise studies of the origin of dark matter, antimatter, and cosmic rays as well as the exploration of new phenomena. Following a 16-year period of construction and testing, and a precursor flight on the Space Shuttle, AMS was installed on the ISS on May 19, 2011. In this report we present results based on 120 billion charged cosmic ray events up to multi-TeV energies. This includes the fluxes of positrons, electrons, antiprotons, protons, and nuclei. These results provide unexpected information, which cannot be explained by the current theoretical models. The accuracy and characteristics of the data, simultaneously from many different types of cosmic rays, provide unique input to the understanding of origins, acceleration, and propagation of cosmic rays.
An excess of ∼10–20 GeV cosmic-ray antiprotons has been identified in the spectrum reported by the AMS-02 Collaboration. The systematic uncertainties associated with this signal, however, have made ...it difficult to interpret these results. In this paper, we revisit the uncertainties associated with the time, charge and energy-dependent effects of solar modulation, the antiproton production cross section, and interstellar cosmic-ray propagation. After accounting for these uncertainties, we confirm the presence of a 4.7σ antiproton excess, consistent with that arising from a mχ≈64–88 GeV dark matter particle annihilating to bb¯ with a cross section of σv≃(0.8–5.2)×10−26 cm3/s. If we allow for the stochastic acceleration of secondary antiprotons in supernova remnants, the data continue to favor a similar range of dark matter models (mχ≈46–94 GeV, σv≈(0.7–3.8)×10−26 cm3/s) with a significance of 3.3σ. The same range of dark matter models that are favored to explain the antiproton excess can also accommodate the excess of GeV-scale gamma rays observed from the Galactic center.
The unprecedented quality of the data collected by the AMS-02 experiment onboard the International Space Station allowed us to address subtle questions concerning the origin and propagation of cosmic ...rays. Here we discuss the implications of these data for the injection spectrum of elements with different masses and for the diffusion coefficient probed by cosmic rays through their journey from the sources to the Earth. We find that the best fit to the spectra of primary and secondary nuclei requires (1) a break in the energy dependence of the diffusion coefficient at energies ∼300 GV; (2) an injection spectrum that is the same for all nuclei heavier than helium, and different injections for both protons and helium. Moreover, if to force the injection spectrum of helium to be the same as for heavier nuclei, the fit to oxygen substantially worsens. Accounting for a small, Xs∼0.4 g cm−2, grammage accumulated inside the sources leads to a somewhat better fit to the B/C ratio but makes the difference between He and other elements even more evident. The statistic and systematic error bars claimed by the AMS collaboration exceed the error that is expected from calculations once the uncertainties in the cross sections of production of secondary nuclei are taken into account. In order to make this point more quantitative, we present a novel parametrization of a large set of cross sections, relevant for cosmic ray physics, and we introduce the uncertainty in the branching ratios in a way that its effect can be easily grasped.
Precise knowledge of the charge and rigidity dependence of the secondary cosmic ray fluxes and the secondary-to-primary flux ratios is essential in the understanding of cosmic ray propagation. We ...report the properties of heavy secondary cosmic ray fluorine F in the rigidity R range 2.15 GV to 2.9 TV based on 0.29 million events collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. The fluorine spectrum deviates from a single power law above 200 GV. The heavier secondary-to-primary F/Si flux ratio rigidity dependence is distinctly different from the lighter B/O (or B/C) rigidity dependence. In particular, above 10 GV, the F/Si/B/O ratio can be described by a power law R^{δ} with δ=0.052±0.007. This shows that the propagation properties of heavy cosmic rays, from F to Si, are different from those of light cosmic rays, from He to O, and that the secondary cosmic rays have two classes.
Cosmic ray models Kachelrieß, M.; Semikoz, D.V.
Progress in particle and nuclear physics,
11/2019, Letnik:
109
Journal Article
Recenzirano
Odprti dostop
We review progress in high-energy cosmic ray physics focusing on recent experimental results and models developed for their interpretation. Emphasis is put on the propagation of charged cosmic rays, ...covering the whole range from ∼(20–50)GV, i.e. the rigidity when solar modulations can be neglected, up to the highest energies observed. We discuss models aiming to explain the anomalies in Galactic cosmic rays, the knee, and the transition from Galactic to extragalactic cosmic rays.
In this work we use the newly reported boron-to-carbon ratio (B/C) from AMS-02 and the time-dependent proton fluxes from PAMELA and AMS-02 to constrain the source and propagation parameters of cosmic ...rays in the Milky Way. A linear correlation of the solar modulation parameter with solar activities is assumed to account for the time-varying cosmic ray fluxes. A comprehensive set of propagation models, with or without reacceleration or convection, has been discussed and compared. We find that only the models with reacceleration can self-consistently fit both the proton and B/C data. The rigidity dependence slope of the diffusion coefficient, δ, is found to be about 0.38–0.50 for the diffusion-reacceleration models. The plain diffusion and diffusion-convection models fit the data poorly. We compare different model predictions of the positron and antiproton fluxes with the data. We find that the diffusion-reacceleration models overproduce low energy positrons, while nonreacceleration models give better fit to the data. As for antiprotons, reacceleration models tend to underpredict low energy antiproton fluxes, unless a phenomenological modification of the velocity dependence of the diffusion coefficient is applied. Our results suggest that there could be important differences of the propagation for nuclei and leptons, in either the Milky Way or the solar heliosphere.
The cosmic rays propagation inside the heliosphere is well described by a transport equation introduced by Parker in 1965. To solve this equation, several approaches were followed in the past. ...Recently, a Monte Carlo approach became widely used in force of its advantages with respect to other numerical methods. In this approach the transport equation is associated to a fully equivalent set of stochastic differential equations (SDE). This set is used to describe the stochastic path of quasi‐particle from a source, e.g., the interstellar space, to a specific target, e.g., a detector at Earth. We present a comparison of forward‐in‐time and backward‐in‐time methods to solve the cosmic rays transport equation in the heliosphere. The Parker equation and the related set of SDE in the several formulations are treated in this paper. For the sake of clarity, this work is focused on the one‐dimensional solutions. Results were compared with an alternative numerical solution, namely, Crank‐Nicolson method, specifically developed for the case under study. The methods presented are fully consistent each others for energy greater than 400 MeV. The comparison between stochastic integrations and Crank‐Nicolson allows us to estimate the systematic uncertainties of Monte Carlo methods. The forward‐in‐time stochastic integrations method showed a systematic uncertainty <5%, while backward‐in‐time stochastic integrations method showed a systematic uncertainty <1% in the studied energy range.
Key Points
Quantitative comparison of backward‐forward‐in‐time cosmic rays transport Monte Carlo methods
Estimation of systematic error of both methods for spectra at 1 AU for energies above 1 GV
Backward‐in‐time method is suited for predicting modulated spectra for high‐precision experiments
The role of cosmic rays generated by supernovae and young stars has very recently begun to receive significant attention in studies of galaxy formation and evolution due to the realization that ...cosmic rays can efficiently accelerate galactic winds. Microscopic cosmic-ray transport processes are fundamental for determining the efficiency of cosmic-ray wind driving. Previous studies modeled cosmic-ray transport either via a constant diffusion coefficient or via streaming proportional to the Alfvén speed. However, in predominantly cold, neutral gas, cosmic rays can propagate faster than in the ionized medium, and the effective transport can be substantially larger; i.e., cosmic rays can decouple from the gas. We perform three-dimensional magnetohydrodynamical simulations of patches of galactic disks including the effects of cosmic rays. Our simulations include the decoupling of cosmic rays in the cold, neutral interstellar medium. We find that, compared to the ordinary diffusive cosmic-ray transport case, accounting for the decoupling leads to significantly different wind properties, such as the gas density and temperature, significantly broader spatial distribution of cosmic rays, and higher wind speed. These results have implications for X-ray, γ-ray, and radio emission, and for the magnetization and pollution of the circumgalactic medium by cosmic rays.
We analyze recent AMS-02 comic-ray measurements of lithium, beryllium, boron, carbon, nitrogen, and oxygen. The emphasis of the analysis is on systematic uncertainties related to propagation and ...nuclear cross sections. To investigate the uncertainties in the propagation scenario, we consider five different frameworks, differing with respect to the inclusion of a diffusion break at a few GV, the presence of reacceleration, and the presence of a break in the injection spectra of primaries. For each framework we fit the diffusion equations of cosmic rays and explore the parameter space with Monte Carlo methods. At the same time, the impact of the uncertainties on the nuclear production cross sections of secondaries is explicitly considered and included in the fit through the use of nuisance parameters. We find that all of the considered frameworks are able to provide a good fit. In particular, two competing scenarios-one including a break in diffusion but no reacceleration and the other with reacceleration but no break in diffusion-are both allowed. The inclusion of cross-section uncertainties is, however, crucial to this result. Thus, at the moment these uncertainties represent a fundamental systematic preventing a deeper understanding of the properties of cosmic-ray propagation. Nonetheless, we find that the slope of diffusion at intermediate rigidities is robustly constrained in the range δ ≃ 0.45 – 0.5 in models without convection, or δ ≃ 0.4 – 0.5 if convection is included in the fit. Furthermore, we find that the use of the AMS-02 beryllium data provides a lower limit on the vertical size of the Galactic propagation halo of zh ≳ 3 kpc .
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