CALET Ultra-Heavy Cosmic-Ray Observations Incorporating Trajectory Dependent Geomagnetic Rigidities

Abstract

CALET Ultra-Heavy Cosmic-Ray Observations Incorporating Trajectory Dependent Geomagnetic Rigidities BRIAN RAUCH, WOLFGANG ZOBER, Washington University, St. Louis, FOR THE CALET COLLABORATION — The CALorimetric Electron Telescope (CALET), launched to the International Space Station (ISS) in August 2015, continues to measure cosmic-ray (CR) electrons, nuclei and gamma-rays. The main calorimeter (CAL) has a 30 radiation length deep calorimeter for high energy electrons that also measures the energy spectra and secondary to primary ratios of the more abundant CR nuclei through 26Fe. The CAL charge detector has the dynamic range to measure CR nuclei from 1H to 40Zr, but to maximize the acceptance of the rare ultra-heavy (UH) CR above 30Zn a special high duty cycle (∼90%) UH trigger is used that does not require passage through the main calorimeter. Forgoing the calorimeter energy measurement provides a ∼6× increase in geometry factor that reduced by ISS obstructions allows CALET to collect in 5 years a UHCR data set similar to that from the first flight of the balloon-borne SuperTIGER instrument. Previous CALET UHCR analyses using time and position corrections based on 26Fe and a geomagnetic vertical cutoff rigidity selection have shown abundances of even nuclei in agreement with SuperTIGER/ACE-CRIS. To further improve resolution and maximize statistics a trajectory dependent geomagnetic rigidity selection is employed here.