Galactic Cosmic-ray Production Research Articles

Evidence for Thermal X-Ray Emission from the Synchrotron-dominated Shocks in Tycho’s Supernova Remnant

Young supernova remnant (SNR) shocks are believed to be the main sites of galactic cosmic-ray production, showing X-ray synchrotron-dominated spectra in the vicinity of their shock. While a faint thermal signature left by the shocked interstellar medium (ISM) should also be found in the spectra, proofs for such an emission in Tycho’s SNR have been lacking. We perform an extended statistical analysis of the X-ray spectra of five regions behind the blast wave of Tycho’s SNR using Chandra archival data. We use Bayesian inference to perform extended parameter space exploration and sample the posterior distributions of a variety of models of interest. According to Bayes factors, spectra of all five regions of analysis are best described by composite three-component models taking nonthermal emission, ejecta emission, and shocked ISM emission into account. The shocked ISM stands out the most in the northern limb of the SNR. We find for the shocked ISM a mean electron temperature keV for all regions and a mean ionization timescale cm−3 s resulting in a mean ambient density cm−3 around the remnant. We performed an extended analysis of the northern limb and show that the measured synchrotron cutoff energy is not well constrained in the presence of a shocked ISM component. Such results cannot currently be further investigated by analyzing emission lines in the 0.5–1 keV range, because of the low Chandra spectral resolution in this band. We show with simulated spectra that Athena X-ray Integral Field Unit future performances will be crucial to address this point.

Nonthermal element abundances at astrophysical shocks

The nonthermal source abundances of elements play a crucial role in the understanding of cosmic ray phenomena from a few GeV up to several tens of EeV . We present a first systematic approach to describe the change of the abundances from the thermal to the nonthermal state via diffusive shock acceleration by a temporally evolving shock. We consider hereby not only ionization states of elements contained in the ambient gas, which we allow to be time dependent due to shock heating, but also elements condensed on solid, charged dust grains which can be injected into the acceleration process as well. Our generic parametrized model is then applied to the case of particle acceleration by supernova remnants in various ISM phases, for which we use state-of-the-art computation packages to calculate the ionization states of all elements. The resulting predictions for low energy cosmic ray (LECR) source abundances are compared with the data obtained by various experiments. We obtain excellent agreement for shocks in warm ionized ISM environments, which include HII regions, if dust grains are injected into the diffusive shock acceleration process with a much higher efficiency than ions. Less dependence of the fit quality is found on the mass-to-charge ratio of ions. For neutral environments, assuming that there are shocks in the weakly ionized component, and for the hot ionized medium we obtain generally inferior fits, but except for the cold neutral medium we do not exclude them as subdominant sites of Galactic cosmic ray production. The key challenge is found to be putting the LECR abundance of pure gas phase elements like neon and the (semi-)volatile elements phosphorus, sulfur and chlorine into the right balance with silicon, calcium and elements of the iron group. We present a brief outlook to the potential consequences of our results for the understanding of the composition around the second knee or the cosmic ray spectrum, or for the viability of explaining ultra-high energy cosmic rays with a dominant contribution by radio galaxies.

Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies

The origin of Galactic cosmic rays (GCRs) remains a mystery after more than one century of their discovery. The diffusive propagation of charged particles in the turbulent Galactic magnetic field makes us unable to trace back to their acceleration sites. Nevertheless, nearby GCR source(s) may leave imprints on the locally measured energy spectra and the anisotropies of the arrival direction. In this work we propose a simple but natural description of the GCR production and propagation, within a two-zone disk-halo diffusion scenario together with a nearby source, to understand the up-to-date precise measurements of the energy spectra and anisotropies of GCRs. We find that a common energy scale of ∼100 TeV appears in both energy spectra of protons and helium nuclei measured recently by CREAM and large-scale anisotropies detected by various experiments. These results indicate that one or more local sources are very likely important contributors to GCRs below 100 TeV . This study provides a probe to identify source(s) of GCRs by means of joint efforts of spectral and anisotropy measurements.

Joint Constraints on Galactic Diffuse Neutrino Emission from the ANTARES and IceCube Neutrino Telescopes

Abstract The existence of diffuse Galactic neutrino production is expected from cosmic-ray interactions with Galactic gas and radiation fields. Thus, neutrinos are a unique messenger offering the opportunity to test the products of Galactic cosmic-ray interactions up to energies of hundreds of TeV. Here we present a search for this production using ten years of Astronomy with a Neutrino Telescope and Abyss environmental RESearch (ANTARES) track and shower data, as well as seven years of IceCube track data. The data are combined into a joint likelihood test for neutrino emission according to the KRA model assuming a 5 PeV per nucleon Galactic cosmic-ray cutoff. No significant excess is found. As a consequence, the limits presented in this Letter start constraining the model parameter space for Galactic cosmic-ray production and transport.

Imaging of SNR IC443 and W44 with the Sardinia Radio Telescope at 1.5 and 7 GHz

Observations of supernova remnants (SNRs) are a powerful tool for investigating the later stages of stellar evolution, the properties of the ambient interstellar medium, and the physics of particle acceleration and shocks. For a fraction of SNRs, multi-wavelength coverage from radio to ultra high-energies has been provided, constraining their contributions to the production of Galactic cosmic rays. Although radio emission is the most common identifier of SNRs and a prime probe for refining models, high-resolution images at frequencies above 5 GHz are surprisingly lacking, even for bright and well-known SNRs such as IC443 and W44. In the frameworks of the Astronomical Validation and Early Science Program with the 64-m single-dish Sardinia Radio Telescope, we provided, for the first time, single-dish deep imaging at 7 GHz of the IC443 and W44 complexes coupled with spatially-resolved spectra in the 1.5-7 GHz frequency range. Our images were obtained through on-the-fly mapping techniques, providing antenna beam oversampling and resulting in accurate continuum flux density measurements. The integrated flux densities associated with IC443 are S_1.5GHz = 134 +/- 4 Jy and S_7GHz = 67 +/- 3 Jy. For W44, we measured total flux densities of S_1.5GHz = 214 +/- 6 Jy and S_7GHz = 94 +/- 4 Jy. Spectral index maps provide evidence of a wide physical parameter scatter among different SNR regions: a flat spectrum is observed from the brightest SNR regions at the shock, while steeper spectral indices (up to 0.7) are observed in fainter cooling regions, disentangling in this way different populations and spectra of radio/gamma-ray-emitting electrons in these SNRs.

The TeV-scale cosmic ray proton and helium spectra: Contributions from the local sources

Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundreds of GeV. This excess is hard to understand in the framework of the conventional models of galactic cosmic ray production and propagation. Here, we propose to explain this anomaly by the presence of local sources. Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar analysis, we consistently derive these fluxes by taking into account both local and remote sources for which a unique injection rate is assumed. We find cosmic ray propagation parameters for which the proton and helium spectra remarkably agree with the PAMELA and CREAM measurements over four decades in energy.

TeV cosmic-ray proton and helium spectra in the myriad model

Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundreds of GeV. This excess is hard to understand in the framework of the conventional models of Galactic cosmic ray production and propagation. We propose here to explain this anomaly by the presence of local sources (myriad model). Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar analysis, we consistently derive these fluxes by taking into account both local and remote sources for which a unique injection rate is assumed. We find cosmic ray propagation parameters compatible with B/C measurements and for which the proton and helium spectra remarkably agree with the PAMELA and CREAM measurements over four decades in energy.

Change of primary cosmic ray mass composition at superhigh energies

The EAS MSU array experimental data are analyzed in relation to the primary cosmic ray composition in the energy range above 1017–1018 eV. The problem of the existence of an additional cosmic ray component, which cannot be explained in the framework of traditional mechanism of Galactic cosmic ray production, is considered. The fraction of gamma-quanta in the primary cosmic radiation is evaluated as well.

Prospects for Galactic TeV Neutrino Astronomy

In just the last few years, the catalog of known Galactic TeV gamma-ray sources has grown dramatically, due to the abilities of current air ¡Cerenkov telescopes to measure both the spectrum and morphology of the TeV emission. While these properties can be very well measured, they are not necessarily sufficient to determine whether the gamma rays are produced by leptonic or hadronic processes. However, if the gamma-ray emission is hadronic, there must be an accompanying flux of neutrinos, which can be determined from the observed gamma-ray spectrum. The upcoming km3 neutrino telescopes will allow for a direct test of the gammaray production mechanism and the possibility of examining the highest possible energies, with important consequences for our understanding of Galactic cosmic-ray production.

Shock-wave and plasma-pinch mechanisms of galactic cosmic-ray production

Based on recent discoveries, we show that it is appropriate to complement the standard shock-wave model for the production of galactic cosmic rays by a plasma-pinch model. The latter describes well the production of high-energy cosmic rays, yields a simple formula for their intensity, and allows the threshold pattern of the knee-type kink in the secondary particle spectrum and a number of unusual phenomena observed above the threshold to be explained.

Could the next generation of cosmology experiments exclude supergravity?

Gravitinos are expected to be produced in any local supersymmetric model. Using their abundance prediction as a function of the reheating energy scale, we argue that the next generation of cosmic microwave background experiments could exclude supergravity or strongly favor ``thermal-like'' inflation models if B mode polarized radiation were detected. Galactic cosmic-ray production by evaporating primordial black holes is also investigated as a way of constraining the Hubble mass at the end of inflation. Subsequent limits on the gravitino mass and on the related grand unification parameters are derived.

Stellar and GCR Production of Lithium in the Milky Way

Lithium production from several stellar sources (C-stars, massive AGB stars, Type II supernovae and novae) as well as from galactic cosmic rays (GCR) is included in a succesfull model for the chemical evolution of the Milky Way in order to predict the evolution of the 7Li abundance (A(Li) = log(7Li/H) + 12) as a function of [Fe/H]. From comparison with the oservational data we infer the following conclusions: 1) Li production from novae seems to be necessary to explain the steep rise of the Li abundance for metallicities larger than [Fe/H] = — 1.0 dex, 2) Li production from SNe II should be less than assumed before in order to reproduce the long plateau observed for A(Li) for low metallicities, 3) Li production from C-stars is negligible relative to Li production from massive AGB stars which is instead a necessary Li- source, 4) Li production from GCR should contribute by no more than 20% to the solar Li abundance.

14C depth profiles in Apollo 15 and 17 cores and lunar rock 68815

Accelerator mass spectrometry (AMS) was used to measure the activity vs. depth profiles of 14C produced by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) in Apollo 15 lunar cores 15001-6 and 15008, Apollo 17 core 76001, and lunar rock 68815. Calculated GCR production rates are in good agreement with 14C measurements at depths below ∼10 cm. Carbon-14 produced by solar protons was observed in the top few cm of the Apollo 15 cores and lunar rock 68815, with near-surface values as high as 66 dpm/kg in 68815. Only low levels of SCR-produced 14C were observed in the Apollo 17 core 76001. New cross sections for production of 14C by proton spallation on O, Si, Al, Mg, Fe, and Ni were measured using AMS. These cross sections are essential for the analysis of the measured 14C depth profiles. The best fit to the activity-depth profiles for solar-proton-produced 14C measured in the tops of both the Apollo 15 cores and 68815 was obtained for an exponential rigidity spectral shape R 0 of 110–115 MV and a 4π flux (J 10, Ep > 10 MeV) of 103–108 protons/cm 2/s. These values of R 0 are higher, indicating a harder rigidity, and the solar-proton fluxes are higher than those determined from 10Be, 26Al, and 53Mn measurements.

Boron in Lithium‐ and Beryllium‐deficient F Stars

The Goddard High Resolution Spectrograph (GHRS) has been used with the Hubble Space Telescope (HST) to observe the B I region at 2497 A in nine F and G dwarfs of approximately solar metallicity. The stars were selected because they have a variety of Li and Be deficiencies. Most of the nine stars were newly observed at high spectral resolution and high signal-to-noise ratios at the Keck I 10 m telescope, the Canada-France-Hawaii 3.6 m telescope, and the University of Hawaii 2.2 m telescope at 3131 A for Be II and 6708 A for Li I. With spectrum synthesis we have determined the abundances of B in our nine program stars and in five other stars from the HST archive. The stellar parameters we have used have been determined in a self-consistent way for the program stars and the archive stars. Spectrum synthesis has also been used to determine the Li and Be abundances or upper limits. Corrections to the B and Li abundances due to non-LTE effects have been applied. The stars originate from the region on the ZAMS of the Li (and Be) dip. In spite of large deficiencies in Li and Be, we find a striking uniformity in the B abundances, i.e., there is no B dip. In all cases the Li deficiency is greater than the Be deficiency. For the coolest and most evolved star in our sample, ζ Her A, the B abundance is 0.6 dex lower than the mean for the other stars. This star also has the largest Be deficiency (more than a factor of 80) and the largest Li deficiency (more than a factor of 600). These data, together with other studies of the Li dip, argue strongly against diffusion and mass loss and in favor of slow mixing as the cause of the Li and Be dip and the absence of a B dip. Six stars with [Fe/H] from -0.75 to +0.15 have Be abundances ranging from the maximum of the sample to a factor of 4 below the maximum, yet these stars have a B/Be ratio that is constant to within ±0.10 dex and that is close to the predictions of Galactic cosmic-ray spallation of 10-15. The Be range for four stars with solar metallicity is still a factor of 2, and yet the B/Be ratio is constant to within ±0.03 dex. These results imply that the Galactic cosmic-ray production of B and Be is not uniform relative to the production of elements such as Fe by stellar nucleosynthesis.

Solar‐flare‐implanted 4He/3;He and solar‐proton‐produced Ne and Ar concentration profiles preserved in lunar rock 61016

Documented near‐surface samples from oriented lunar rock 61016 have yielded the first measurements of depth profiles for 21Ne, 22Ne, and 38Ar isotopes produced in situ from nuclear interactions of energetic solar flare protons. Further, the cosmogenic 21Ne/22Ne ratios are distinct for different proton energy ranges and increase systematically with increasing shielding. This variation in cosmogenic 21Ne/22Ne represents a progression from a mixed component produced from solar flare protons (SCR) and galactic cosmic rays (GCR) to a pure GCR component. Using the 2 m.y. exposure age for 61016, the calculated production rates for SCR 21Ne and 38Ar from solar energetic protons in near‐surface samples agree within 5% and 25%, respectively, with theoretical estimates. Calculated GCR production rates for 21Ne and 38Ar in the deepest (26 mm) samples agree within 25% and 10%, respectively, with theoretical estimates. Combined SCR and GCR concentration profiles for 21Ne, 22Ne, and 38Ar match theoretical calculations based on an omnidirectional flux above 10 MeV of 100 protons cm−2 s−1 with an exponential rigidity between 70 and 85 MV and a surface erosion rate of 1 mm m.y.−1. Selectively etched, near‐surface samples suggest a long‐term average 4He/3He ratio of ∼770 for implanted solar flare nuclei with E > ∼4 MeV amu−1, and a 4He/³He ratio of ∼3450 for solar flare nuclei with E > ∼1 MeV amu−1. Averaged over long term, the solar flare 4He/3He ratio appears energy dependent.

Overview of Cosmic Rays, Solar and Interplanetary Physics Research (1987 – 1990)

A brief survey of recent U.S. investigations in the field of heliospheric plasmas and their manifestations is presented, introducing the following collection of detailed reviews (accessions A91-46959 to A91-46964). Topics examined include the large-scale structure of interplanetary plasmas, models of Galactic cosmic-ray production and propagation, solar-wind turbulence, long-period solar-terrestrial variability, the possible relation between solar-neutrino counts and the sunspot cycle, X-ray studies of solar flares and their implications for solar processes, and the near-sun magnetic field.

26Al depth profile in Apollo 15 drill core

Cosmic-ray-produced 26Al ( t 1/2 = 7.05 × 10 5 years) has been measured in the Apollo 15 long core (surface to 390 g/cm 2—218 cm) for study of galactic cosmic ray production profiles, using accelerator mass spectrometry. The results are in general accord with non-destructive counting data obtained earlier, but systematically lower, and significantly higher precision. From this experiment the half-attenuation length for 26Al production can be calculated to be 122 g/cm 2 (150–400 g/cm 2 region) after normalizing the data to average chemical composition. The 53Mn ( t 1/2 = 3.7 × 10 6 years) production profile in deep cores was also compiled to date. The half-attenuation length for 53Mn production was calculated to be 123 g/cm 2 (150–400 g/cm 2 region).

10Be and 36Cl depth profiles in an Apollo 15 drill core

Cosmic-ray-produced 10Be ( t 1/2 = 1.6 × 10 6 years) and 36Cl ( t 1/2 = 3.0 × 10 5 years) have been measured in the Apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry. From these experiments, the half-attenuation length for 10Be production and 36Cl production were calculated to be 120 g/cm 2 and 132 g/cm 2 (150–400 g/cm 2 region). The measured half-attenuation length for 10Be is slightly longer than that predicted by the Reedy-Arnold theoretical model. The flatter and somewhat deeper maximum seen in the 36Cl profile compared to the 10Be, 26Al and 53Mn profiles can be explained by production from secondary thermal neutrons on 35Cl.

Cosmogenic 21Ne and 22Ne depth profiles in chondrites

The production rate profiles of 21Ne and 22Ne as a function of depth in meteoroids due to spallation by solar flare cosmic rays (SCR) and galactic cosmic rays (GCR) are calculated and their dependence on size and composition of meteoroids has been evaluated. The GCR production rate at a given depth increases with size for radii <25cm and then decreases whereas the 22Ne 21Ne ratio (NeR) generally decreases with size and depth. The calculated GCR production rates and NeR are consistent with the measurements in several Chondrites. A plot of track production rate vs. NeR shows that some chondrites have NeR values smaller than those expected for their sizes. Thes obeervation suggests at least a two-stage irradiation for such meteorites; the meteoroid exposure as a small body in the interplanetary space must have been preceded by exposure under deep shielding, possibly in its parent body.

Neon and argon in the Allende meteorite

Trapped and cosmogenic Ne and Ar were measured in Ca,Al-rich aggregates and chondrules, mafic chondrules, and bulk and matrix samples from the Allende C3V chondritic meteorite to investigate the possible occurrence of anomalous isotopic compositions of noble gases that would correlate with oxygen or magnesium isotopic anomalies previously found in this meteorite. Large enrichments of both 22Ne and 36Ar were observed in low-temperature release fractions from several Ca,Al-rich inclusions, but the enrichments are consistent with galactic cosmic-ray production of 22Ne by spallation from sodium and 36Ar by neutron capture on chlorine. Trapped neon in matrix samples is comprised of two distinctive compositions, with ( 20Ne/ 22Ne) t equal to 8.7 ± 0.1 and 10.4 ± 1.0, that appear to correlate with the two gas-rich trace phases chromite/carbon and ‘Q’ described by Lewis et al. (1975). Several Ca,Al-rich aggregates which have high contents of the volatile elements Na, Cl, K, and Rb also contain trapped neon. However, no neon-E has been identified in any of the samples studied, including samples of several inclusions known to contain isotopically anomalous oxygen and magnesium.