Cosmic Ray Nuclei Research Articles

ENERGY SPECTRA OF PRIMARY AND SECONDARY COSMIC-RAY NUCLEI MEASURED WITH TRACER

The TRACER cosmic-ray detector, first flown on long-duration balloon (LDB) in 2003 for observations of the major primary cosmic-ray nuclei from oxygen (Z=8) to iron (Z=26), has been upgraded to also measure the energies of the lighter nuclei, including the secondary species boron (Z=5). The instrument was used in another LDB flight in 2006. The properties and performance of the modified detector system are described, and the analysis of the data from the 2006 flight is discussed. The energy spectra of the primary nuclei carbon (Z=6), oxygen, and iron over the range from 1 GeV amu$^{-1}$ to 2 TeV amu$^{-1}$ are reported. The data for oxygen and iron are found to be in good agreement with the results of the previous TRACER flight. The measurement of the energy spectrum of boron also extends into the TeV amu$^{-1}$ region. The relative abundances of the primary nuclei, such as carbon, oxygen, and iron, above $\sim10$ GeV amu$^{-1}$ are independent of energy, while the boron abundance, i.e. the B/C abundance ratio, decreases with energy as expected. However, there is an indication that the previously reported $E^{-0.6}$ dependence of the B/C ratio does not continue to the highest energies.

Cosmogenic gamma rays and the composition of cosmic rays

We discuss the prospects of detecting the sources of ultrahigh energy (UHE) cosmic ray (CR) nuclei via their emission of cosmogenic $\ensuremath{\gamma}$ rays in the GeV to TeV energy range. These $\ensuremath{\gamma}$ rays result from electromagnetic cascades initiated by high energy photons, electrons, and positrons that are emitted by CRs during their propagation in the cosmic radiation background and are independent of the simultaneous emission of $\ensuremath{\gamma}$ rays in the vicinity of the source. The corresponding production power by UHE CR nuclei (with mass number $A$ and charge $Z$) is dominated by pion photo production ($\ensuremath{\propto}A$) and Bethe-Heitler pair production ($\ensuremath{\propto}{Z}^{2}$). We show that the cosmogenic $\ensuremath{\gamma}$-ray signal from a single steady UHE CR source is typically more robust with respect to variations of the source composition and injection spectrum than the accompanying signal of cosmogenic neutrinos. We study the diffuse emission from the sum of extragalactic CR sources as well as the point-source emission of the closest sources.

10Be Production in the Atmosphere by Galactic Cosmic Rays

Galactic cosmic ray nuclei and energetic protons produced in solar flares and accelerated by coronal mass ejections are the main sources of high-energy particles of extraterrestrial origin in near-Earth space and inside the Earth’s atmosphere. The intensity of galactic cosmic rays inside the heliosphere is strongly influenced by the modulation of the interstellar source particles on their way through interplanetary space. Among others, this modulation depends on the activity of the Sun, and the resulting intensity of the energetic particles in the atmosphere is an indicator of the solar activity. Therefore, rare isotopes found in historical archives and produced by spallation reactions of primary and secondary hadrons of cosmic origin in the atmosphere, so-called cosmogenic nuclides, can be used to reconstruct the solar activity in the past. The production rate of 10Be, one of the cosmogenic nuclides most adequate to study the solar activity, is presented showing its variations with geographic latitude and altitude and the dependence on different production cross-sections present in literature. In addition, estimates for altitude integrated production rates of 10Be at different locations since the early nineteen sixties are shown.

Cosmic ray composition studies through the Gerasimova-Zatsepin effects of heavy nuclei at LAAS

Extensive air showers (EASs) originated from pri- mary cosmic ray energies above 10 15 eV have been measured at multiple EAS observatories deployed in Japan since Sept. 1996. The typical EAS array has been located at the rooftop of the buildings in the university campus, and has GPS- disciplined 10 MHz oscillator to provide the UTC time stamp for each EAS event within a few µs accuracies. Searching for simultaneous and parallel EAS events at multiple EAS observatories due to Gerasimova-Zatsepin (GZ) effects have been carried out by comparing EAS arrival time stamps and directions detected by several baseline combinations of EAS arrays. The EAS pairs whose time difference and angular distance were less than 5 ms and less than 15 respectively, were se- lected and their angular distances from the solar direction and the lunar direction were examined. The data were com- pared with numerical GZ probability as a function of arrival directions of cosmic ray nuclei. Consequently, significant excesses of these events in the solar direction as expected in the numerical prediction of GZ effects were not found. We however found that the deficiencies of EAS pairs in the lunar direction, but its deviation is not significant.

Solar modulation of the spectra of protons and helium nuclei in the PAMELA experiment

We present the energy spectra of protons and helium nuclei of cosmic rays obtained in the PAMELA experiment on board the satellite RESURS-DK1 for the period from August 2006 to December 2009. The spectra were measured in the energy range of 100 MeV/nucleon to 100 GeV/nucleon using a magnetic spectrometer within the apparatus. Variations in the solar modulation potential for protons and helium nuclei were calculated on the basis of the monthly mean particle fluxes. A force field model was used to compare the modulation with measurements from balloon experiments, and with measurements from a network of neutron monitors.

The TRACER instrument: A balloon-borne cosmic-ray detector

We describe a large-area detector for measurements of the intensity of cosmic-ray nuclei in balloon-borne exposures. In order to observe individual nuclei at very high energies, the instrument employs transition radiation detectors (TRD) whose energy response extends well beyond 104 GeV amu−1. The TR measurement is performed with arrays of single-wire proportional tubes interleaved with plastic-fiber radiators. An additional energy determination comes from the specific ionization in gas and its relativistic rise which is also measured with proportional tubes. The tubes also determine the trajectory of each cosmic-ray nucleus with mm-resolution. In total, nearly 1600 tubes are used. The instrument is triggered by large-area plastic scintillators. The scintillators, together with acrylic Cherenkov counters, also determine the nuclear charge Z of each cosmic-ray particle, measure the energy in the GeV amu−1 region, and discriminate against low-energy background. We describe the details of this detector system, and discuss its performance in three high-altitude balloon flights, including two long-duration flights in 2003 and 2006 at Antarctic and Arctic latitudes, respectively. Scientific results from these flights are summarized, and possible future developments are reviewed.

A possible correlation between the high-energy electron spectrum and the cosmic ray secondary-to-primary ratios

Recent observations of high energy cosmic-ray electrons by the Fermi-LAT and the HESS experiments between $20$ GeV and $5$ TeV have found that the energy spectrum closely follow a broken power-law with a break at around $1$ TeV. On the other hand, measurements of cosmic-ray secondary-to-primary ratios like the boron-to-carbon ratio seem to indicate a possible change in the slope at energies around $100$ GeV/n. In this paper, we discuss one possible explanation for the observed break in the electron spectrum and its possible correlation with the flattening in the secondary-to-primary ratios at higher energies. In our model, we assume that cosmic-rays after acceleration by supernova remnant shock waves, escape downstream of the shock and remain confined within the remnant until the shock slows down. During this time, the high-energy electrons suffer from radiative energy losses and the cosmic-ray nuclei undergo nuclear fragmentations due to their interactions with the matter. Once the cosmic-rays are released from the supernova remnants, they follow diffusive propagation in the Galaxy where they further suffer from radiative or fragmentation losses.

Spacetime noncommutativity and ultrahigh energy cosmic ray experiments

If new physics were capable of pushing the neutrino-nucleon inelastic cross section 3 orders of magnitude beyond the standard model prediction, then ultrahigh energy (UHE) neutrinos would have already been observed at neutrino observatories. We use such a constraint to reveal information on the scale of noncommutativity (NC) ${\ensuremath{\Lambda}}_{\mathrm{NC}}$ in noncommutative gauge field theories where neutrinos possess a tree-level coupling to photons in a generation-independent manner. In the energy range of interest (${10}^{10}$ to ${10}^{11}\text{ }\text{ }\mathrm{GeV}$), the $\ensuremath{\theta}$ expansion ($|\ensuremath{\theta}|\ensuremath{\sim}1/{\ensuremath{\Lambda}}_{\mathrm{NC}}^{2}$) and, therefore, the perturbative expansion, in terms of ${\ensuremath{\Lambda}}_{\mathrm{NC}}$, retains no longer its meaningful character, forcing us to resort to those NC field theoretical frameworks involving the full $\ensuremath{\theta}$ resummation. Our numerical analysis of the contribution to the process coming from the photon exchange impeccably pins down a lower bound on ${\ensuremath{\Lambda}}_{\mathrm{NC}}$ to be as high as 900 (450) TeV, depending on the estimates for the cosmogenic neutrino flux. If, on the other hand, one considers a surprising recent result that occurred in Pierre Auger Observatory data, that UHE cosmic rays are mainly composed of highly ionized Fe nuclei, then our bounds get weaker, due to the diminished cosmic neutrino flux. Nevertheless, we show that, even for the very high fraction of heavy nuclei in primary UHE cosmic rays, our method may still yield remarkable bounds on ${\ensuremath{\Lambda}}_{\mathrm{NC}}$, typically always above 200 TeV. Albeit, in this case, one encounters a maximal value for the Fe fraction, from which any useful information on ${\ensuremath{\Lambda}}_{\mathrm{NC}}$ can be drawn, delimiting thus the applicability of our method.

Measuring fluxes of the protons and helium nuclei of high-energy cosmic rays

Techniques for measuring helium nuclei and proton energy spectra in circumterrestrial space were developed on the basis of simulated data and data from the position-sensitive silicon-tungsten calorimeter in the PAMELA satellite experiment. The thickness of the calorimeter is 0.6 nuclear interaction lengths. In this work, the experimental results for the measured energy spectra of the protons and helium nuclei of cosmic rays with energies above 50 GeV are presented.

Classifying groups of PCR nuclei with energies of 1015–1016 eV according to the spatial-angular distribution of EAS Cherenkov light

Multidimensional Bayesian classification criteria are proposed for groups of nuclei of primary cosmic rays based on characteristics of spatial-angular distribution of Cherenkov light of extensive air showers. These criteria allow us in principle to separate no less than 50–60% of the primary protons from heavier nuclei; the classification errors for primary protons and groups of nitrogen and iron nuclei total no more than several per cent. New parameters that substantially improve the separability of classes of showers are also found for angular images of Cherenkov light.

Lorentz invariance violation and chemical composition of ultra high energy cosmic rays

Motivated by experimental indications of a significant presence of heavy nuclei in the cosmic ray flux at ultra high energies (≳1019 eV), we consider the effects of Planck scale suppressed Lorentz Invariance Violation (LIV) on the propagation of cosmic ray nuclei. In particular we focus on LIV effects on the photodisintegration of nuclei onto the background radiation fields. After a general discussion of the behavior of the relevant quantities, we apply our formalism to a simplified model where the LIV parameters of the various nuclei are assumed to kinematically result from a single LIV parameter for the constituent nucleons, η, and we derive constraints on η. Assuming a nucleus of a particular species to be actually present at 1020 eV the following constraints can be placed: −3 × 10−2≲η≲4 for 56Fe, −2 × 10−3≲η≲3 × 10−2 for 16O and −7 × 10−5≲η≲1 × 10−4 for 4He, respectively.

Normalized ionization yield function for various nuclei obtained with full Monte Carlo simulations

Several recent results important for production of ion pairs in the Earth atmosphere by various primary cosmic ray nuclei are presented. The direct ionization by various primary cosmic ray nuclei is explicitly obtained. The longitudinal profile of atmospheric cascades is sensitive to the energy and mass (charge) of the primary particle. In this study different cosmic ray nuclei are considered as primaries, namely Helium, Oxygen and Iron nuclei. The cosmic ray induced ionization is obtained on the basis of CORSIKA 6.52 code simulations using FLUKA 2006 and QGSJET II hadronic interaction models. The energy of the primary particles is normalized to GeV per nucleon. In addition, the ionization yield function Y is normalized as ion pair production per nucleon. The obtained ionization yield functions Y for various primaries are compared. The presented results and their application are discussed.

TeV ELECTRON SPECTRUM FOR PROBING COSMIC-RAY ESCAPE FROM A SUPERNOVA REMNANT

One of the most essential but uncertain processes for producing cosmic-rays (CRs) and their spectra is how accelerated particles escape into the interstellar space. We propose that the CR electron spectra at >~TeV energy can provide a direct probe of the CR escape complementary to the CR nuclei and gamma-rays. We calculate the electron spectra from a young pulsar embedded in the supernova remnant (SNR), like Vela, taking into account the energy-dependent CR escape. SNRs would accelerate and hence confine particles with energy up to 10^{15.5}eV. Only energetic particles can escape first, while the lower energy particles are confined and released later. Then the observed electron spectrum should have a low energy cutoff whose position marks the age of the pulsar/SNR. The low energy cutoff is observable in the $\gtrsim {\rm TeV}$ energy window, where other contaminating sources are expected to be few due to the fast cooling of electrons. The spectrum looks similar to a dark matter annihilation line if the low energy cutoff is close to the high energy intrinsic or cooling break. The future experiments such as CALET and CTA are capable of directly detecting the CR escape features toward revealing the origin of CRs.

EVIDENCE FOR PARTICLE ACCELERATION TO THE KNEE OF THE COSMIC RAY SPECTRUM IN TYCHO ’S SUPERNOVA REMNANT

Supernova remnants (SNRs) have long been assumed to be the source of cosmic rays (CRs) up to the "knee" of the CR spectrum at 10^15 eV, accelerating particles to relativistic energies in their blast waves by the process of diffusive shock acceleration (DSA). Since cosmic ray nuclei do not radiate efficiently, their presence must be inferred indirectly. Previous theoretical calculations and X-ray observations show that CR acceleration modifies significantly the structure of the SNR and greatly amplifies the interstellar magnetic field. We present new, deep X-ray observations of the remnant of Tycho's supernova (SN 1572, henceforth Tycho), which reveal a previously unknown, strikingly ordered pattern of non-thermal high-emissivity stripes in the projected interior of the remnant, with spacing that corresponds to the gyroradii of 10^14 - 10^15 eV} protons. Spectroscopy of the stripes shows the plasma to be highly turbulent on the (smaller) scale of the Larmor radii of TeV energy electrons. Models of the shock amplification of magnetic fields produce structure on the scale of the gyroradius of the highest energy CRs present, but they do not predict the highly-ordered pattern we observe. We interpret the stripes as evidence for acceleration of particles to near the knee of the CR spectrum in regions of enhanced magnetic turbulence, while the observed highly ordered pattern of these features provides a new challenge to models of DSA.

Meteorites as a natural detectors of very heavy galactic cosmic ray nuclei: some aspects of the experimental track studies

Meteorites as a natural detectors of very heavy galactic cosmic ray nuclei: some aspects of the experimental track studies

Analytic solutions of ultrahigh energy cosmic ray nuclei revisited

The chemical composition of ultra-high energy cosmic rays is a key question in particle astrophysics. The measured composition, inferred from the elongation rates of cosmic ray showers, looks in general very different from the initial source composition: resonant photo-disintegration in the cosmic radiation background proceeds rapidly at the highest energies and the initial composition quickly becomes lighter during propagation. For a statistical analysis of continuously improving cosmic ray data it is desirable to know the secondary spectra as precisely as possible. Here, we discuss exact analytic solutions of the evolution equation of ultra-high energy cosmic ray nuclei. We introduce a diagrammatic formalism that leads to a systematic analytic expansion of the exact solution in terms of second order effects of the propagation. We show how the first order corrections of this expansion can improve the predictions of secondary spectra in a semi-analytical treatment.

On the problem of lunar radiation environment

In connection with projects of manned bases on the Moon it becomes topical to estimate radiation danger for their inhabitants. In this paper we describe a method of evaluation of the radiation environment on the lunar surface produced by galactic and solar cosmic rays. The roles of both primary and secondary radiations generated in the depth of the lunar soil under the action of high-energy protons and nuclei are taken into account. Calculated fluxes of particles are used in order to estimate annual averaged absorbed and equivalent local dose rates in tissues. It is established that in the lunar rock the contribution of secondary neutrons to the dose rate exceeds that of protons. The contribution of the secondary particles generated by nuclei of galactic cosmic rays to the dose rate is estimated.

Implications of the cosmic ray electron spectrum and anisotropy measured with Fermi-LAT

The Fermi Large Area Telescope (LAT) collaboration recently released the updated results of the measurement of the cosmic ray electron (CRE) spectrum and published its first constraints on the CRE anisotropy. With respect to the previous Fermi-LAT results, the CRE spectrum measurement was extended down from 20 to 7 GeV, thus providing a better lever arm to discriminate theoretical models. Here we show that the new data strengthen the evidence for the presence of two distinct electron and positron spectral components. Furthermore, we show that under such hypothesis most relevant CRE and positron data sets are remarkably well reproduced. Consistent fits of cosmic-ray nuclei and antiproton data, which are crucial to validate the adopted propagation setup(s) and to fix the solar modulation potential, are obtained for the Kraichnan and plain-diffusion propagation setups, while the Kolmogorov one is disfavored. We then confirm that nearby pulsars are viable source candidates of the required e ± extra-component. In that case, we show that the predicted CRE anisotropy is compatible with Fermi-LAT constraints and that a positive detection should be at hand of that observatory. Models assuming that only nearby supernova remnants contribute to the high energy tail of the observed CRE spectrum are in contrast with anisotropy limits.

Charge spectrum of galactic cosmic ray nuclei as measured in meteorite olivines

This paper presents experimental results on galactic cosmic ray nuclei in olivine crystals from the Marjalahti and Eagle Station pallasites. The charge spectrum of the nuclei is measured to be in good agreement with the experimental data from the HEAO-3 and ARIEL-6satellite missions.

RECORD-SETTING COSMIC-RAY INTENSITIES IN 2009 AND 2010

We report measurements of record-setting intensities of cosmic-ray nuclei from C to Fe, made with the Cosmic Ray Isotope Spectrometer carried on the Advanced Composition Explorer in orbit about the inner Sun–Earth Lagrangian point. In the energy interval from ∼70 to ∼450 MeV nucleon−1, near the peak in the near-Earth cosmic-ray spectrum, the measured intensities of major species from C to Fe were each 20%–26% greater in late 2009 than in the 1997–1998 minimum and previous solar minima of the space age (1957–1997). The elevated intensities reported here and also at neutron monitor energies were undoubtedly due to several unusual aspects of the solar cycle 23/24 minimum, including record-low interplanetary magnetic field (IMF) intensities, an extended period of reduced IMF turbulence, reduced solar-wind dynamic pressure, and extremely low solar activity during an extended solar minimum. The estimated parallel diffusion coefficient for cosmic-ray transport based on measured solar-wind properties was 44% greater in 2009 than in the 1997–1998 solar-minimum period. In addition, the weaker IMF should result in higher cosmic-ray drift velocities. Cosmic-ray intensity variations at 1 AU are found to lag IMF variations by 2–3 solar rotations, indicating that significant solar modulation occurs inside ∼20 AU, consistent with earlier galactic cosmic-ray radial-gradient measurements. In 2010, the intensities suddenly decreased to 1997 levels following increases in solar activity and in the inclination of the heliospheric current sheet. We describe the conditions that gave cosmic rays greater access to the inner solar system and discuss some of their implications.