All-particle Spectra Research Articles

Massive star cluster origin for the galactic cosmic ray population at very-high energies

ABSTRACT We demonstrate that supernova remnant (SNR) shocks embedded within massive star clusters can reproduce both the cosmic-ray proton and all-particle spectra measured in the vicinity of the Earth up to hundreds of peta-electronvolts (PeV). We model two classes of massive star clusters. The first population are ‘loose clusters’ that do not power a collective wind termination shock. SNR shocks then expand in a low-density and weakly magnetized medium, and this population mainly contributes up to the ‘knee’ of the CR spectrum around 1 PeV. The second population are young compact clusters, which are powerful and compact enough to sustain a collective wind outflow. SNR shocks then expand from the cluster into the strongly magnetized wind and accelerate nuclei up to ultra-high energies. This population, representing only about 15 per cent of all Galactic massive star clusters, nevertheless dominates the spectrum between ∼1 and 100 PeV. While these two components alone can reproduce the shape of the CR spectrum up to hundreds of PeV, adding a light subankle extragalactic component motivated by composition and anisotropy measurements, allows to reproduce the spectrum up to the highest energies. Fitting parameters are systematically linked to physical variables whose values are in line with theoretical expectations.

Cosmic ray spectrum and composition from PeV to EeV using 3 years of data from IceTop and IceCube

We report on measurements of the all-particle cosmic ray energy spectrum and composition in the PeV to EeV energy range using three years of data from the IceCube Neutrino Observatory. The IceTop detector measures cosmic ray induced air showers on the surface of the ice, from which the energy spectrum of cosmic rays is determined by making additional assumptions about the mass composition. A separate measurement is performed when IceTop data are analyzed in coincidence with the high-energy muon energy loss information from the deep in-ice IceCube detector. In this measurement, both the spectrum and the mass composition of the primary cosmic rays are simultaneously reconstructed using a neural network trained on observables from both detectors. The performance and relative advantages of these two distinct analyses are discussed, including the systematic uncertainties and the dependence on the hadronic interaction models, and both all-particle spectra as well as individual spectra for elemental groups are presented.

On the knee of Galactic cosmic rays in light of sub-TeV spectral hardenings**Supported by National Key Research and Development Program of China (2016YFA0400200), the National Natural Science Foundation of China (11635011, 11761141001, 11663006, 11722328) and the 100 Talents program of Chinese Academy of Sciences

More than fifty years after the discovery of the knee in the cosmic ray (CR) spectra, its physical origin remains a mystery. This is partly due to the ambiguity of the energy spectra of individual components. Recently, direct measurements from several space experiments found significant spectral hardenings of CR nuclei at ∼200 GV. A joint modeling of the direct and indirect measurements may help to understand the experimental systematics and the physics of the knee. In this work, we update the phenomenological “poly-gonato” model to include the spectral hardenings, with a changing spectral index of γ + β · log E. This modification gives a reasonable description of the CR spectra in a wide energy range. However, the fits to different data sets give different results. We find that the fit to the AMS-02 and CREAM data slightly favors a relatively low energy knee of the light components. In such a case, the expected all-particle spectra under-shoot the data, which may require an extra component of CRs. The fits to AMS-02 data and the light component (H+He) data from the Tibet ASγ/ARGO-YBJ/WFCTA and KASCADE experiments give consistent results with the all-particle spectra. We further propose a possible physical realization of such a “modified poly-gonato” model of spectral hardenings by means of spatially-dependent diffusion of CRs. We find reasonably good agreement between the model predictions and the data for CR spectra, the secondary-to-primary ratios, and the amplitude of anisotropies.

Cosmic ray spectrum and composition from three years of IceTop and IceCube

IceTop is the surface component of the IceCube Observatory, composed of frozen water tanks at the top of IceCube’s strings. Data from this detector can be analyzed in different ways with the goal of measuring cosmic ray spectrum and composition. The shower size S125 from IceTop alone can be used as a proxy for primary energy, and unfolded into an all-particle spectrum. In addition, S125 from the surface can be combined with high-energy muon energy loss information from the deep IceCube detector for those air showers which pass through both. Using these coincident events in a complementary analysis, both the spectrum and mass composition of primary cosmic rays can be extracted in parallel using a neural network. Both of these analyses have been performed on three years of IceTop and IceCube data. Both all-particle spectra as well as individual spectra for elemental groups are presented.

Measurement of the cosmic ray all-particle and light-component energy spectra with the ARGO-YBJ experiment

ARGO-YBJ preliminary results of the measurements of the all-particle and light-component (i.e. protons and helium) cosmic ray energy spectra between approximately 5 TeV and 5 PeV are reported and discussed. The resulting all-particle spectrum (measured in the energy range 100TeV - 3PeV) is in good agreement with both theoretical parametrizations and previous measurements. The light-component (i.e. p + He) has been measured with high resolution up to about 5 PeV. The preliminary result is in agreement with direct measurements and then show a clear indication of a bending below 1PeV. Improvements of event selection/reconstruction with the full statistics and a complete analysis of systematic uncertainties is currently under way.

Reconciling the light component and all-particle cosmic ray energy spectra at the knee**Supported by NSFC (11175147)

The knee phenomenon of the cosmic ray spectrum, which plays an important role in studying the acceleration mechanism of cosmic rays, is still an unsolved mystery. We try to reconcile the knee spectra measured by ARGO-YBJ and Tibet-III. A simple broken power-law model fails to explain the experimental data. Therefore a modified broken power-law model with non-linear acceleration effects is adopted, which can describe the sharp knee structure. This model predicts that heavy elements dominate at the knee.

Measurement of the Cosmic Ray spectra by the ARGO-YBJ experiment

Exploiting the features and location at high altitude (the Cosmic Ray Observatory of Yangbajing in Tibet, China, at about 4,300 m a.s.l.) of the ARGO-YBJ detector, the study of several aspects concerning cosmic ray physics in the primary energy region 1012–1016 eV has been performed. Here, the preliminary results of the measurement of all-particle and light-component (i.e. protons and helium nuclei) energy spectra between few tens TeV and ∼5 PeV will be reported, as obtained from the data of RPC (Resistive Plate Chamber) analog charge readout. The study of such energy region is particularly important to better understand the so called knee of the energy spectrum and its origin, as well as for a powerful cross-check among very different experimental techniques, like balloon/space-borne spectrometers and surface air shower detectors. It also allows to test the hadronic interaction models currently used for investigating particle and cosmic ray physics up the highest energies. Finally, the precise measurements of the cosmic ray energy spectrum and composition make possible a more reliable estimation of the atmospheric neutrino flux, which is crucial for any extra-terrestrial neutrino search.

Measurement of the cosmic ray all-particle and light-component energy spectra with the ARGO-YBJ experiment

The ARGO-YBJ detector, located at high altitude in the Cosmic Ray Observatory of Yangbajing in Tibet (4300 m asl, about 600 g/cm2 of atmospheric depth) provides the opportunity for the study, with unprecedented resolution, of cosmic ray physics in the primary energy region between 1012 and 1016 eV. Preliminary results of the measurements of the all-particle and light-component (i.e. protons and helium) energy spectra between approximately 5 TeV and 5 PeV are reported and discussed.

Measurement of the cosmic ray all-particle and light-component energy spectra with the ARGO-YBJ experiment

The ARGO-YBJ detector, located at high altitude in the Cosmic Ray Observatory of YangBaJing in Tibet (4300 m asl, about 600 g/cm2 of atmospheric depth) provides the opportunity for the study, with unprecedented resolution, of cosmic ray physics in the primary energy region between 1012 and 1016 eV. Preliminary results of the measurements of the all-particle and light-component (i.e. protons and helium) energy spectra between approximately 5 TeV and 5 PeV are reported and discussed.

Light and Heavy Cosmic-Ray Mass Group Energy Spectra as Measured by the MAKET-ANI Detector

Standard models of cosmic-ray origin link the space accelerators of our Galaxy to the supernova remnants (SNRs)—expanding shells driven by very fast blast waves, usually with gamma-ray pulsars near the morphological center. Energy spectra of fully stripped ions with charges from Z = 1 to Z = 26 can provide clues to the validity of the standard model. Unfortunately, smeared data from the extensive air shower experiments do not provide enough information for such ion spectroscopy. Nonetheless, the measurement of energy spectra of two or three broad mass groups (so-called light, intermediate, and heavy) will allow us to prove or disprove the rigidity-dependent acceleration. Recently, using multidimensional classification methods, the all-particle spectra from the MAKET-ANI experiment on Mount Aragats, in Armenia, was categorized into two distinct primary mass groups. We present, for the first time, the light and heavy nuclei spectra from the MAKET-ANI experiment.

On the knee in the energy spectrum of cosmic rays

The knee in the all-particle energy spectrum is scrutinized with a phenomenological model, named poly-gonato model, linking results from direct and indirect measurements. For this purpose, recent results from direct and indirect measurements of cosmic rays in the energy range from 10 GeV up to 1 EeV are examined. The energy spectra of individual elements, as obtained by direct observations, are extrapolated to high energies using power laws and compared to all-particle spectra from air shower measurements. A cut-off for each element proportional to its charge Z is assumed. The model describes the knee in the all-particle energy spectrum as a result of subsequent cut-offs for individual elements, starting with the proton component at 4.5 PeV, and the second change of the spectral index around 0.4 EeV as due to the end of stable elements ( Z=92). The mass composition, extrapolated from direct measurements to high energies, using the poly-gonato model, is compatible with results from air shower experiments measuring the electromagnetic, muonic, and hadronic components. But it disagrees with the mass composition derived from X max measurements using Čerenkov and fluorescence light detectors.