Effects of Solar Modulation on the Low-Energy Cosmic Ray Antiproton/Proton Ratio

We examine the transport of cosmic-ray protons and anitprotons from local interstellar space through the interplanetary medium to Earth and discuss the resulting effects on the low-energy antiproton/proton ratio at 1 AU. We find that the antiproton/proton ratio at energies above ~3 GeV is a useful diagnostic of cosmic-ray transport in the Galaxy. However, at energies below ~1 GeV the expected ratio is much more uncertain because of differences in the energy spectra and the resulting relative modulation of protons and antiprotons over the solar cycle, as well as uncertainties in the interstellar spectra. Using calculated interstellar spectra as references, we find that the antiproton/proton ratio at low energies varies by as much as an order of magnitude over the solar cycle. As a result, we recommend that attention be given instead to interpretation of the measured cosmic-ray antiproton energy spectrum rather than to the antiproton/proton ratio

Interpretation of the Low-Energy Cosmic Ray Antiproton/Proton Ratio

We examine the solar modulation of cosmic ray protons and antiprotons, and discuss the resulting effects on the low-energy antiproton/proton ratio at 1 AU. We find that the anitiproton/proton ratio at energies >3 GeV is a useful diagnostic of cosmic ray transport in the Galaxy. However, at energies <l GeV the expected ratio is much more uncertain because of variation in the relative modulation of protons and antiprotons and uncertainties in the interstellar spectra. As a result, it is recouunended that attention be given instead to interpretation of the cosmic ray antiproton energy spectrum measured rather than to the antiproton/proton ratio

HNX/SuperTIGER Silicon Strip Detector Response to Nuclei in Lead Primary and Fragmented Test Beams

The response to 150 GeV/nuc primary lead (^(208)Pb) and fragmented (A/Z=2.4, 2.2, 2.0) beams measured a silicon strip detector, designed for use in the Heavy Nuclei eXplorer (HNX) and an upgrade of the Super Trans-Iron Galactic Element Recorder (SuperTIGER) balloon experiment, was evaluated in a CERN test beam (H8A) during Nov - Dec 2018. The 500 μm thick, single-sided silicon detectors have 32 DC-coupled strips with 3 mm pitch on the junction side with 9.6×9.6 cm^2 active area. Discrete charge-preamplifiers and shaping amplifiers were used to read out the ohmic and junction side signals simultaneously using the SuperTIGER DAQ system. We report on the response in a configuration where all 32 strips were joined and read out together. The strip detector-under-test was situated between planar silicon detectors, which provided the charge selection as well as a comparison of the measured response of each detector. The combined data set shows excellent charge resolution and finely resolved elemental peaks from helium (Z=2) through lead (Z=82). In this paper, we provide a description of the test beam experiment and the results of the charge resolution analysis

The SUPERTIGER Instrument: Measurement of Elemental Abundances of Ultra-Heavy Galactic Cosmic Rays

The SuperTIGER (Super Trans-Iron Galactic Element Recorder) instrument was developed to measure the abundances of galactic cosmic-ray elements from _(10)Ne to _(40)Zr with individual element resolution and the high statistics needed to test models of cosmic-ray origins. SuperTIGER also makes exploratory measurements of the abundances of elements with 40 29 and ∼60 with Z >49. Here, we describe the instrument, the methods of charge identification employed, the SuperTIGER balloon flight, and the instrument performance

STEREO and ACE Observations of Energetic Particles from Corotating Interaction Regions

Since early 2007, significant particle enhancements due to corotating interaction regions (CIRs) have regularly appeared at 1 AU without any appreciable contamination from solar energetic particles (SEPs). In 2009 the prevalence of CIRs diminished as the maximum speed of the high speed solar wind streams in the ecliptic decreased along with the tilt of the heliospheric current sheet. Observations of CIR time profiles at different longitudes from STEREO show delays between the Behind and Ahead spacecraft that are often roughly as expected from the corotation time lag, although small differences in the spacecraft latitudes introduce significant scatter in the time delays. In some cases different features seen at Ahead and Behind suggest that transient disturbances in the solar wind may alter connection to or transport from the shock, or that temporal changes occur in the CIR shock itself. H and He data from STEREO/LET at 1.8–6 MeV/nucleon show that 1) the CIR spectral index at these energies is ~−4, independent of intensity but with considerable variability, 2) the He/H ratio is ~0.03 for larger CIRs but varies systematically with energy and event intensity, and 3) although the correlation between the CIR MeV particle increases and solar wind speed is generally good, many times a high-speed stream is not associated with MeV particles, while at other times a recurring series of CIR particle increases appears only at higher energies and may be associated with current sheet crossings and low speed solar wind

STEREO Observations of Energetic Neutral Hydrogen Atoms During the 2006 December 5 Solar Flare

We report the discovery of energetic neutral hydrogen atoms (ENAs) emitted during the X9 solar event of 2006 December 5. Beginning ~1 hr following the onset of this E79 flare, the Low Energy Telescopes (LETs) on both the STEREO A and B spacecraft observed a sudden burst of 1.6-15 MeV protons beginning hours before the onset of the main solar energetic particle event at Earth. More than 70% of these particles arrived from a longitude within ±10° of the Sun, consistent with the measurement resolution. The derived emission profile at the Sun had onset and peak times remarkably similar to the GOES soft X-ray profile and continued for more than an hour. The observed arrival directions and energy spectrum argue strongly that the particle events < 5 MeV were due to ENAs. To our knowledge, this is the first reported observation of ENA emission from a solar flare/coronal mass ejection. Possible origins for the production of ENAs in a large solar event are considered. We conclude that the observed ENAs were most likely produced in the high corona and that charge-transfer reactions between accelerated protons and partially stripped coronal ions are an important source of ENAs in solar events

Galactic Cosmic Ray Origins and OB Associations: Evidence from SuperTIGER Observations of Elements 26_{26}Fe through 40_{40}Zr

We report abundances of elements from $_{26}$Fe to $_{40}$Zr in the cosmic radiation measured by the SuperTIGER (Trans-Iron Galactic Element Recorder) instrument during 55 days of exposure on a long-duration balloon flight over Antarctica. These observations resolve elemental abundances in this charge range with single-element resolution and good statistics. These results support a model of cosmic-ray origin in which the source material consists of a mixture of 19$^{+11}_{-6}$\% material from massive stars and $\sim$81\% normal interstellar medium (ISM) material with solar system abundances. The results also show a preferential acceleration of refractory elements (found in interstellar dust grains) by a factor of $\sim$4 over volatile elements (found in interstellar gas) ordered by atomic mass (A). Both the refractory and volatile elements show a mass-dependent enhancement with similar slopes.Comment: 9 pages, 12 figures, 2 tables, accepted by Ap

Solar Energetic Particle Spectral Breaks

The five large solar particle events during October–November 2003 presented an opportunity to test shock acceleration models with in-situ observations. We use solar particle spectra of H to Fe ions, measured by instruments on ACE, SAMPEX, and GOES-11, to investigate the Q/M-dependence of spectral breaks in the 28 October 2003 event. We find that the break energies scale as (Q/M)^b with b ≈ 1.56 to 1.75, somewhat less than predicted. We also conclude that SEP spectra >100 MeV/nucleon are best fit by a double power-law shape. ©2005 American Institute of Physic