Session W13: Cosmic Ray Experiments and Detections

The CALET ISS High Energy Cosmic Ray Experiment: Nuclei Energy Spectra

The CALET high energy cosmic ray space experiment has been operating as an attached payload on the International Space Station (ISS) Japanese Experiment Module – Exposed Facility (JEM-EF) for more than 6 years. While the CALET design emphasizes the precise investigations of cosmic ray electrons beyond ~5 TeV, the instrument has also been used to study the energy spectra of cosmic ray nuclei from protons to the iron peak near 1,000 TeV.  We summarize the instrument performance and discuss the CALET energy spectrum measurements for H, C, O, and Fe nuclei and compare CALET results with measurements reported by other experiments. In particular, we discuss the shape of the spectra at high energies including multiple changes in the H, C, and O spectral index. Our present Fe observations are consistent with a single power law up to 2 TeV / nucleon and above this limit our present statistical and systematic error limit our ability to draw conclusions about possible deviations.   

Use of Energy Measurements in the CALET Ultra-Heavy Cosmic-Ray Analysis

The Calorimetric Electron Telescope (CALET), launched to the ISS in August 2015 and in continuous operation since, measures cosmic-ray (CR) electrons, nuclei, and gamma rays. CALET, with its 27 radiation length deep Total Absorption Calorimeter (TASC), measures particle energy, allowing for the determination of spectra and secondary to primary ratios of the more abundant CR nuclei through ₂₈Ni, while the main charge detector (CHD) can measure Ultra-Heavy (UH) CR nuclei through ₄₀Zr. Previous CALET UHCR analyses have used a special high duty cycle (~90%) UH trigger that does not require passage through the TASC. After 6 years of operation, the size of the UH data set is comparable to the first flight of the balloon-borne SuperTIGER instrument without the need for an atmospheric correction. Previous analysis has used time- and position-dependent detector response corrections based on ₁₄Si and ₂₆Fe and an angle-dependent geomagnetic cutoff rigidity selection to show abundances of even nuclei in agreement with SuperTIGER. This analysis improves resolution by restricting UH events to the ~1/6 that pass through both the TASC and CHD, providing energy information for the charge determination. Our results are compared to previous CALET work as well as ACE-CRIS, SuperTIGER, and HEAO-3.   

IceAct: Low energy extension for cosmic ray measurements at the IceCube Neutrino Observatory

The IceAct telescopes are prototype Imaging Air Cherenkov telescopes (IACTs) situated at the IceCube Neutrino Observatory at the geographic South Pole. Imaging Air Cherenkov Telescopes are capable of measuring the electromagnetic component of an air shower by detecting the Cherenkov light emitted within the atmosphere. This gives IceAct the opportunity to complement the air showers detection of the electromagnetic footprint measured by the surface array, IceTop, and the high energy muonic component measured by the in-ice detector, IceCube. Since January 2019, two prototype IceAct telescopes with 61 SiPM pixels apiece are taking data during the austral winter. These two telescopes provide the opportunity to study detector performance of Imaging Air Cherenkov Telescopes in the harsh conditions at the South Pole, and to study hybrid events with the existing detector components. Therefore different machine learning algorithms like graph neural networks and random forest trees are used to reconstruct the air shower properties.  We will present the current status and the future plans for the IceAct telescopes at the South Pole.   

Indirect observational constraints on UHECR source environments

We present new constraints on the environments surrounding UHECR accelerators, obtained by combining a realistic and flexible phenomenological UHECR source model with the latest UHECR spectrum & composition data and constraints from neutrinos and gammas. Our analysis provides a new set of criteria on the magnetic field, size, and temperature of UHECR source environments. These criteria (distinct from the Hillas criterion for the UHECR accelerator) will be compared to observational data to infer which astrophysical source candidates are preferred or excluded by multimessenger data.   

Ultra-High Energy Cosmic Ray Energy Spectrum using Hybrid Analysis with TAx4

Cosmic rays are subatomic particles of extraterrestrial origin and at the

highest energies, they are not well understood. The variation of the

cosmic ray flux with energy is referred to as the "Energy Spectrum.” The

measurement of the cosmic ray energy spectrum is important because it

may give a hint of where cosmic rays come from. The Telescope Array

(TA) Cosmic Ray Observatory, located in Millard County Utah, is the

largest cosmic ray detector in the Northern hemisphere. Following

evidence for a hotspot in the arrival directions of the highest energy

cosmic rays, TA underwent the TAx4 upgrade to expand the area of

Surface Detectors (SD) by a factor of 4. The upgrade included new

Fluorescence Detector (FD) stations to view over the expanded SD

arrays. In this work, I will present a preliminary cosmic ray energy

spectrum using hybrid events from TAx4, the hybrid resolutions of the

detector, and data-MC comparisons. I will show this work's preliminary

hybrid energy spectrum is in agreement with previous TA

measurements, which is a key first step towards future composition and

anisotropy studies.    

The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS)

TIGERISS is a future space-based ultra-heavy galactic cosmic ray (UHGCR) mission to be proposed to the NASA Astrophysics Pioneers program with heritage from the long-duration balloon-borne TIGER and SuperTIGER experiments.  TIGERISS incorporates silicon detector technology in place of scintillators, increasing the dynamic range for charge measurement without saturation.  From a vantage point on the ISS and a geometrical factor between 1.1 and 1.7 m2sr depending on attachment point, TIGERISS will accumulate in one year statistics up to 56Ba with significance comparable to current SuperTIGER results without the need for atmospheric propagation corrections.

SuperTIGER results up to 40Zr support a model of CR origins in OB Associations, selective acceleration of refractory elements in dust grains, and the expected charge dependence from grain sputtering injection of CRs into SN shocks.  Above 40Zr this model breaks down, and a change in acceleration mechanism and/or an additional r-process source (potentially neutron star mergers, now known sites of r-process nucleosynthesis) is needed.  TIGERISS will measure CR abundances from 5B to 82Pb, probing the relative contributions of r-process sites to the CR reservoir and searching for further evidence of a change in CR sources at high Z.   

CREAM LED Data Analysis

The Cosmic Ray Energetics And Mass (CREAM) experiment is designed to measure the cosmic ray elemental spectra for Z=1-26 nuclei at energies ranging from ~ 10^12 to 10^15 GeV. CREAM had 7 successful balloon flights over Antarctica and it was later installed on the International Space Station. For energy measurements, the CREAM instrument uses a calorimeter (CAL). The CAL has 20 layers of 50 scintillating fiber ribbons used to detect showers produced by cosmic ray interactions. These ribbons are read out using 40 pixelated Hybrid Photodiodes (HPD). Each HPD consists of 73 pixels, 3 of which receive optical signals from Light Emitting Diodes (LED). These LEDs are used for checking channel aliveness and the HPD pixel-to-fiber alignment. Channel gains were measured by varying high voltages from 3 to 10.5 kV, DAC values from 6000 to 9000, and bias voltage on and off. Analysis results will be presented.