Energy and nuclear charge dependence of abundance enhancements of solar cosmic ray heavy ions in three large solar events

The differential flux and energy spectra of solar cosmic ray heavy ions of He, C, O, Ne, Mg, Si, and Fe were determined in the energy interval E = 3–30 MeV amu^-1 for two large solar events of January 24, 1971 and September 1, 1971 in rocket flights made from Ft. Churchill. From these data the relative abundances and the abundance enhancement factors, ξ, relative to photospheric abundances were obtained for these elements. Similar results were obtained for a third event on August 4, 1972 from the available published data. Characteristic features of ξ vs nuclear charge dependences were deduced for five energy intervals. The energy dependence of ξ for He shows a moderate change by a factor of about 3, whereas for Fe, ξ shows a very dramatic decrease by a factor of 10–20 with increasing energy. It is inferred that these abundance enhancements of solar cosmic ray heavy ions at low energies seem to be related to their ionization states (Z ^*) and hence studies of Z ^* can give information on the important parameters such as temperature and density in the accelerating region in the Sun.     

Measurements of cosmic-ray Li,Be and B nuclei in the energy range 100 MeV/nuc to >22 BeV/nuc

We report on new measurements of the spectra of Li, Be and B nuclei in the primary cosmic radiation in the energy range 100 MeV/nuc to >22 BeV/nuc. The differential spectrum of these light nuclei is found to have a maximum at 400 MeV/nuc in 1966. The L/M ratio is found to be equal to 0.25±0.01, constant over the entire energy range of the measurement. Atmospheric and solar modulation effects on the L nuclei and the L/M ratio are discussed. It is concluded that this ratio is representative of conditions in interstellar space. Using the most recently available fragmentation parameters gives a material path length of 3.6 g/cm² of hydrogen for the particles producing the L nuclei. The absence of any variation of the L/M ratio with energy places severe constraints on models for the propagation of cosmic rays. Models in which the material path length is a strong function of energy — or that exhibit an exponential path-length distribution for a fixed energy are incompatible with these results. An examination of the abundance ratios of the individual L nuclei separately reveals major discrepancies with the predictions of interstellar diffusion theory based on presently accepted fragmentation parameters. The constancy of the measured Li/M and B/M ratios with energy is not in accord with the large energy dependence of these ratios expected from the energy dependence of the fragmentation cross-sections. The low Li/M ratio and high B/M ratio to be expected if these nuclei are created at a much lower energy than we observe are also not found. This presents difficulties for theories which suggest that the passage through matter has occurred at low energies subsequently followed by considerable acceleration.The Be/M ratio in cosmic rays is anomalous in that it is 40% larger than expected on the basis of the fragmentation cross-sections. Evidence presented here on the isotopic composition of Be nuclei suggests that this discrepancy is due to an enhanced abundance of Be⁹ or Be¹⁰ in cosmic rays. This discrepancy complicates the determination of a cosmic-ray age using the decay of Be¹⁰ into B.Nevertheless the Be/B ratio is observed to remain constant at 0.42±0.03 over the energy range from 100 MeV/nuc to over 10 BeV/nuc. Unless the fragmentation parameters into the various isotopes of Be and B are such that e.g. (Be/B)<0.05 as a result of this decay, then the age of cosmic rays is either >3×10⁸ years or <10⁶ years. The further observation that the mass to charge ratio of all Be nuclei of energy 1 BeV/nuc is =2.05±0.1 suggests that Be¹⁰ is present at these energies. This supports the idea of a short lifetime.     

Perspective of monochromatic gamma-ray line detection with the High Energy cosmic-Radiation Detection (HERD) facility onboard China’s space station

HERD is the High Energy cosmic-Radiation Detection instrument proposed to operate onboard China’s space station in the 2020s. It is designed to detect energetic cosmic ray nuclei, leptons and photons with a high energy resolution ( ∼1% for electrons and photons and 20% for nuclei) and a large geometry factor (>3 m² sr for electrons and diffuse photons and > [2]m² sr for nuclei). In this work we discuss the capability of HERD to detect monochromatic γ-ray lines, based on simulations of the detector performance. It is shown that HERD will be one of the most sensitive instruments for monochromatic γ-ray searches at energies between ∼ 10 to a few hundred GeV. Above hundreds of GeV, Cherenkov telescopes will be more sensitive due to their large effective area. As a specific example, we show that a good portion of the parameter space of a supersymmetric dark matter model can be probed with HERD.     

Cosmic ray studies with a gas Cherenkov counter in association with an ionization spectrometer

The results from a ballon-borne gas Cherenkov counter (threshold 16.5 GeV nuc^–1) and an ionization spectrometer are presented. The gas Cherenkov counter provides an absolute energy calibration for the response of the calorimeter for 5Z26 nuclei of cosmic rays. The contribution of scintillation to the gas Cherenkov pulse height has been obtained by independently selecting particles below the gas Cherenkov threshold using the ionization spectrometer. Energy spectra were derived by minimizing the ² between a Monte Carlo simulated data and flight data. Best fit power laws (dN/dE=AE ^–) were determined for C, N, O, Ne, Mg, and Si. The power laws, all consistent withE ^–2.7, are not good fits to the data. A better fit is obtained using the spectrum derived from the spectrometer. The data from the ionization calorimeter (Simonet al., 1979) and the gas Cherenkov are thus completely self-consistent.On sabbatical leave from the University of Maryland.     

The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray showers detected by the Pierre Auger Observatory

In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an Extensive Air Shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 10¹⁷ and 10¹⁹ eV and zenith angles up to 65°. A parametrization combining a step function with an exponential is found to reproduce them very well in the considered range of energies and zenith angles. The LTP functions can also be obtained from data using events simultaneously observed by the fluorescence and the surface detector of the Pierre Auger Observatory (hybrid events). We validate the Monte Carlo results showing how LTP functions from data are in good agreement with simulations.     

Sub-iron to iron nuclei in low-energy (50–200 MeV nucl−1) cosmic rays as observed in the Skylab experiment

In this paper we present our most recent results on the sub-iron (Sc to Cr) to Fe nuclei abundance ratios in the low-energy cosmic rays of 50 to 250 MeV nucl.^–1 and their implications as observed in theSkylab experiment. In view of the importance of this ratio in determining the cosmic-ray pathlength in interstellar medium, we have obtained additional data in the same detector module and the results of final analysis are reported. Charge determinations in the Lexan detector were made from an average of about four independent measurements ofZ for each of the cosmic-ray events and the mean charge resolution is obtained asZ/Z0.2. From about 100 events of calcium to nickel in low-energy cosmic rays, sub-iron (Sc to Cr) to Fe–Co ratio is determined as 1.43±0.40 in 50–250 MeV nucl.^–1. This shows a large energy dependence of the ratio as compared to the value of 0.4–0.8 in 200–1000 MeV nucl.^–1 as measured by many investigators. The origin of this large enhancement of the ratios in low-energy cosmic rays is not known at present. Some possible suggestions are briefly mentioned.     

Cherenkov τ shower earth-skimming method for PeV–EeV ντ observation with Ashra

We describe a method of observation for PeV–EeV τ neutrinos using Cherenkov light from the air showers of decayed τs produced by τ neutrino interactions in the Earth. Aiming for the realization of neutrino astronomy utilizing the Earth-skimming τ neutrino detection technique, highly precise determination of arrival direction is key due to the following issues: (1) clear identification of neutrinos by identifying those vertices originating within the Earth’s surface and (2) identification of very high energy neutrino sources. The Ashra detector uses newly developed light collectors which realize both a 42°-diameter field-of-view and arcminute resolution. Therefore, it has superior angular resolution for imaging Cherenkov air showers. In this paper, we estimate the sensitivity of and cosmic-ray background resulting from application of the Ashra-1 Cherenkov τ shower observation method. Both data from a commissioning run and a long-term observation (with fully equipped trigger system and one light collector) are presented. Our estimates are based on a detailed Monte Carlo simulation which describes all relevant shower processes from neutrino interaction to Cherenkov photon detection produced by τ air showers. In addition, the potential to determine the arrival direction of Cherenkov showers is evaluated by using the maximum likelihood method. We conclude that the Ashra-1 detector is a unique probe into detection of very high energy neutrinos and their accelerators.     

Cosmic ray acceleration in hypernova remnants expanding in wind bubbles of Wolf-Rayet progenitor stars

The determination of the origin of cosmic rays with observed energies in excess of 10¹⁷ eV that exceed the expected energies of cosmic rays accelerated by supernova remnants in the galaxy is a pressing problem in modern astrophysics. Hypernova remnants are one of the possible galactic sources of cosmic rays with energies of up to 10¹⁹ eV. Hypernovae constitute a class of extremely powerful supernova explosions, whose supposed progenitors are massive Wolf-Rayet stars. We analyze the special aspects of acceleration of cosmic rays in hypernova remnants that expand in wind bubbles of Wolf-Rayet progenitor stars. We show that these cosmic rays may attain maximum energies of 10¹⁸ eV even with a relatively conservative choice of acceleration parameters and account for tens of percent of the total cosmic ray flux observed in the vicinity of the earth in the energy range of 10¹⁶–10¹⁸ eV if the galactic hypernova explosion rate in the modern epoch reaches ? _S ～ 10^?4 year^?1.     

Studies of the chemical composition of cosmic rays withZ=3–30 at high and low energies

We have measured the chemical composition of cosmic rays withZ2 over an energy range from 100 MeV/nuc to >2 GeV/nuc using 2 new large area counter telescopes. One of these instruments was a 4 element dE/dx×E× Range telescope, the other a 4 element dE/dx×Cerenkov× ×Range telescope. Two balloon flights with these telescopes at Ft. Churchill in the summer of 1970 provided a total of nearly 1000 Fe nuclei with a charge resolution ranging from 0.10 charge unit at Carbon to 0.25 charge unit at Fe. A detailed charge spectrum is obtained at both high and low energies. Some important differences exist between the present results and those obtained earlier, due in part to the improved statistical accuracy and in part to the improved background rejection of the present data. In particular, the abundance of Cr and Mn are each found to be 0.10×Fe in contrast to the earlier ratio of 0.30 found by some workers for each of these nuclei. The abundance of these two nuclei, as well as others in the 15–25 range, shows no strong dependence on energy. We have extrapolated our composition data to the cosmic ray sources using a variety of interstellar path length distributions. The abundances ofall secondary nuclei withZ between 3–25 are consistent only with propagation models which have vacuum path length distributions which do not differ greatly from exponential. The source abundances of nuclei withZ=15, 17, 18, 19, 21, 22, 23, 24, and 25 are found to be <0.02×Fe. For the remaining nuclei, Na, Al, S, and Ca are found to have source abundances of 0.07, 0.11, 0.18 and 0.13 of Fe respectively. The source abundance of C and O relative to Fe is also much different than some earlier compilations. A comparison of solar and cosmic ray abundances reveals certain selective differences, rather than a systematic overabundance of heavy nuclei in cosmic rays, as has been suggested in the past. These differences are discussed in terms of a common nucleosynthesis origin of the two species of particles.Research sponsored by the National Aeronautics and Space Administration under Grant No. NGR-30-002-052.     

Simulation studies of MACE-I: Trigger rates and energy thresholds

The MACE (Major Atmospheric Cherenkov Experiment) is an upcoming Very High Energy (VHE) γ-ray telescope, based on imaging atmospheric Cherenkov technique, being installed at Hanle, a high altitude astronomical site in Ladakh, India. Here we present Monte Carlo simulation studies of trigger rates and threshold energies of MACE in the zenith angle range of 0°–60° for on-axis γ-ray coming from point source and various cosmic ray species. We have simulated the telescope’s response to γ-rays, proton, electron and alpha initiated atmospheric Extensive Air Showers (EAS) in the broad energy range of 5 GeV to 20 TeV. For γ-rays we consider power law and log parabolic spectra while other particles are simulated with their respective cosmic ray spectrum. Trigger rates and threshold energies are estimated for the trigger configuration of 4 Close Cluster Nearest Neighbour(CCNN) pixels as implemented in MACE hardware, in combination with single channel discriminator threshold ranging from 6–10 photo electrons (pe). We find that MACE can achieve the γ-ray trigger energy threshold of ∼ 17 GeV (4 CCNN, 9 pe) at 0° zenith angle for power law spectrum. The total trigger rate at 0° zenith is expected to be ∼650 Hz, with protons contributing ∼ 80% to it. For the zenith range of 0°-40° we find that the telescope can achieve γ-ray trigger threshold energies of ∼22 GeV at 20° zenith angle and ∼40 GeV at 40° zenith angle. Integral rates are also almost constant for this zenith angle range. At zenith angle of 60°, trigger energy threshold increases to ∼173 GeV and total integral rate falls down to ∼305 Hz.     

Origin of cosmic rays: Galactic models with halo

Many years ago physical and radio-astronomical arguments and data led to the assumption that cosmic rays in the Galaxy (and probably in other galaxies) fill a more or less extended halo, but are not concentrated in the disk. It was not so long ago, however, that the existence of a radio-halo was discovered, in which the effective dimensions increase with a decrease in frequency. The frequency decrease occurs when relativistic electrons diffuse from the disk, losing energy due to bremsstrahlung and Compton scattering.Meanwhile, some ambiguity on the question of the existence of a radio-halo, and other reasons, have led to a rather wide use of disk models, particularly those in which cosmic rays are present in the Galaxy only for a periodT _cr,d3×10⁶ yr. The authors have repeatedly stated the inadmissibility of such models and, generally, a homogeneous (leaky box) model for the origin of cosmic rays. The new data concerning the amount of radioactive¹⁰Be nuclei in cosmic rays near the Earth in no way contradict the halo models in which the lifetime of cosmic rays isT _cr,h10⁸ yr. In connection with the continuing controversy, the present paper is devoted to a detailed consideration of the difference between the homogeneous and diffusion models. Within the latter models some calculations on the chemical composition of cosmic rays have been carried out, which concern not only stable but also radioactive isotopes.     

A new method to reconstruct the energy and determine the composition of cosmic rays from the measurement of Cherenkov light and particle densities in extensive air showers

A Monte Carlo study to reconstruct energy and mass of cosmic rays with energies above 300 TeV using ground based measurements of the electromagnetic part of showers initiated in the atmosphere is presented. The shower properties determined with two detector arrays measuring the air Cherenkov light and the particle densities as realized at the HEGRA experiment are processed to determine the energy of the primary particle without the need of any hypothesis concerning its mass. The mass of the primary particle is reconstructed coarsely from the same observables in parallel to the energy determination.     

The cascading of cosmic-ray nuclei in various media

More than a thousand interactions of primary heavy nuclei of the cosmic radiation with charge ≥10 and energy >1 GeV nucleon^?1 in nuclear emulsion have been studied with emphasis on how the primary nucleus fragments. It has been determined that the cases of multiple successive fragmentations that have been observed do not occur more frequently than expected. The fragmentation ofZ>20 nuclei does depend on the target nucleus to some extent so it is important to try to separate the interactions in emulsion by theirN _h (number of evaporation prongs). The fragmentation of ₈ ¹⁶ O at 2.1 GeV nucleon^?1 measured at the Bevalac shows a similar dependence on target nucleus. By using data from these new interactions combined with published data we have simulated on a computer nuclear cascades in both emulsion and air. Results on these cascades are given for both primary silicon and primary iron nuclei. These results are used to discuss the fluctuations expected in extensive air showers produced by heavy primary nuclei.     

Fission and the <Emphasis Type="Italic">r</Emphasis>-process: The rates of induced and delayed fission

The most recent fission-barrier calculations based on improved mass formulas indicate that the adopted values are underestimated. We analyze the dependence of the fission rates on the fission barrier and show that an increase in the fission barriers leads not so much to a decrease in the importance of fission as to the possible synthesis of heavier elements in the r-process. The rates of induced fission of most isotopes with Z>80 at astrophysical energies have been calculated for the first time for fission barriers obtained from different theoretical models.     

Instrumentation for very high energy gamma-ray astronomy

Considerable progress has been made in the last half-decade in the field of very high energy (VHE) gamma-ray astronomy (photons with energies between 10¹¹ and 10¹³ eV). The high background level due to the isotropic cosmic ray flux which has bedevilled the field since its inception in the early 1960's can now be reduced to such a degree that significant gamma-ray signals from several sources become visible within a few hours of observation. The instrumentation and methodologies which have made this possible are reviewed. A brief historical introduction is followed by a summary of the salient properties of the atmospheric Cherenkov flash associated with VHE gamma-ray events. The major components of a VHE gamma-ray astronomy telescope are then reviewed. This is followed by a discussion of the different methodologies currently being used to discriminate against the cosmic ray background. Properties of several specific installations are then summarized, and possible future developments in VHE instrumentation are briefly discussed.     

Exposure History of H5 Chondrite Gujargaon

Abstract— Cosmic ray produced tracks, He and Ne isotopes and radionuclides have been studied in the recently fallen H5 chondrite Gujargaon. The results indicate an exposure age of about 7 Ma. The high track production rates of 0.25 to 0.69 × 10⁶ cm^?2 Ma^?1 suggest that the Gujargaon meteoroid had a small size (Re = 9–10 cm) in space and suffered 1–3 cm ablation in the atmosphere. The conclusion about the meteoroid size is supported by the low activity of neutron capture isotope ⁶⁰Co and high spallogenic ²²Ne/²¹Ne ratio of about 1.25. The data on long lived isotopes ¹⁰Be, ⁵³Mn and ²⁶Al are used to derive production rates of these isotopes in a rock having a radius of 9 cm and the activity levels of the short lived isotopes ²²Na and ⁵⁴Mn are used to estimate the effect of modulation of galactic cosmic rays at the time of solar maximum of 1982.     

Search for short cosmic gamma-ray bursts using data from the APEX and LILAS experiments onboard the Phobos-2 interplanetary spacecraft

A statistical analysis of the spectral and temporal parameters for 546 triggering events on the APEX gamma-ray detector onboard the Phobos-2 spacecraft has revealed a group of 28 events that are probably short cosmic gamma-ray bursts (GRBs). The distribution of the full group of 74 events of the APEX experiment in duration parameter is bimodal in shape, which is in good agreement with the bimodal shape of the BATSE GRB distribution. A search for the detected group of short events using data from the LILAS X-ray and soft gamma-ray detector onboard the same spacecraft has yielded no positive result. A comparison of the APEX and LILAS data has led us to conclude that the short GRBs have a significantly reduced soft gamma-ray flux at energies <100 keV relative to the power law dN/dE=CE^?α with the average index α=2.62.     

Performance of a scintillation detector array operated with LHAASO-KM2A electronics

A scintillation detector array composed of 115 detectors and covering an area of about 20000 m² was installed at the end of 2016 at the Yangbajing international cosmic ray observatory and has been taking data since then. The array is equipped with electronics from Large High Altitude Air Shower Observatory Square Kilometer Complex Array (LHAASO-KM2A) and, in turn, currently serves as the largest debugging and testing platform for the LHAASO-KM2A. Furthermore, the array was used to study the performance of a wide field-of-view air Cherenkov telescope by providing accurate information on the shower core, direction and energy, etc. This work is mainly dealing with the scintillation detector array. The experimental setup and the offline calibration are described in detail. Then, a thorough comparison between the data and Monte Carlo (MC) simulations is presented and a good agreement is obtained. With the even-odd method, the resolutions of the shower direction and core are measured. Finally, successful observations of the expected Moon’s and Sun’s shadows of cosmic rays (CRs) verify the measured angular resolution.     

Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Dust particles in interplanetary space are expected to charge up to an electrostatic potential of about +5 V mostly by the solar UV (Horányi, 1996, Annu. Rev. Astrophys. 34, 383). Since the dynamics of charged grains may be quite different from neutral particles, the knowledge of the grain charge Q_d is highly desirable. In the last two decades, several detectors on spacecraft were flown to measure the dust charge in-situ, but the instrumentation was not capable of determining the dust charge unambiguously. The Cosmic Dust Analyser (CDA) on the Cassini spacecraft includes a charge sensitive entrance grid system (QP detector). While entering the instrument, sufficiently charged particles induce a characteristic charge feature onto the grid system, which allows a reliable determination of Q_d as well as of the impact speed v_d. Here we report the first successful in-situ measurement of charged interplanetary dust grains by CDA. Amongst 37 impacts by interplanetary grains registered between November 1999 and January 2000, we identified 6 impacts whose QP signals show a clear feature caused by charged grains, corresponding to Q_d between 1.3 and 5.4 fC. Knowledge of Q_d also allows us to estimate the grain mass m_d. Assuming a potential of φ_d≈+5 V and spheroidal grain morphologies with ratios of the maximum size to the minimum size of less than 2 the masses derived from Q_d were found to be in excess of 10⁻¹³ kg. The dynamics of such particles are dominated by the Sun's gravity. In the framework of the micro-meteoroid models of the Solar System these grains belong to the core population of interplanetary grains (Divine, 1993, J. Geophys. Res. 98, 17029). Furthermore, a rate of 6 impacts of grains with m_d?10⁻¹³ kg during 107 days is in good agreement with the predictions of the interplanetary dust environment model by Staubach et al. (1997, Adv. Space Res. 19, 301). This result demonstrates that charge detectors as the CDA QP system offer a reliable in-situ technique for determining simultaneously both the mass and velocity of big interplanetary grains. The primary CDA subsystem to determine m_d and v_d, however, is an impact ionisation detector. The majority of the 37 recorded dust impacts produced impact charges are well outside the calibrated range. Moreover, these impacts were usually characterised by impact ionisation signals which differ significantly from signals taken in calibration experiments. In this paper we took advantage of the fact that the measurement of Q_d is not affected by the subsequent impact of the grain with the detector. By relating m_d and v_d derived from Q_d of the 6 QP impactors to their corresponding ionisation signals we show that in many cases even for energetic impacts outside the calibrated range meaningful values for the dust mass can be obtained. The observed deviations of the ionisation signals from the calibration measurements are likely due to the large amount of plasma generated by such impacts. We discuss the implications of these findings on a meaningful reduction of impact ionisation signals caused by big particle impacts. A new scheme to identify and to evaluate such signals is presented. These finding are of great importance for future Cassini measurements in the saturnian system.     

SODIUM-22, 26AI,AND 10Be IN 3He-RICH FLARES

The theory of ³He-rich flares by Colgate, Audouze, and Fowler implies that the composition of the solar cosmic ray-event associated with a ³He-rich flare is grossly non-solar. The relative abundances (relative to hydrogen) of carbon, nitrogen, and oxygen, as well as those of heavier elements are significantly reduced, and the isotopic compositions of virtually all elements are bound to be strongly anomalous. In addition, the abundances of ²²Na, ²⁶Al, and ¹⁰Be (of which there are approximately 10²⁵atoms each in a ³He-rich flare) are at least comparable to the abundances of stable isotopes of these elements. Conditions for the detectability of the three radioactive species are discussed.