Characteristics and Performance of the CALorimetric Electron Telescope (CALET) Calorimeter for Gamma-Ray Observations

Abstract

The CALorimetric Electron Telescope primary detector (CALET-CAL) is a 30 radiation-length-deep hybrid calorimeter designed for the accurate measurement of high-energy cosmic rays. It is capable of triggering on and giving near complete containment of electromagnetic showers from primary electrons and gamma rays from 1 GeV to over 10 TeV. The first 24 months of on-orbit scientific data (2015 November 01-2017 October 31) provide valuable characterization of the performance of the calorimeter based on analyses of the gamma-ray data set in general and bright point sources in particular. We describe the gamma-ray analysis, the expected performance of the calorimeter based on Monte Carlo simulations, the agreement of the flight data with the simulated results, and the outlook for long-term gamma-ray observations with the CAL.

High-Energy Gamma-ray Observations Using the CALorimetric Electron Telescope (CALET) on the ISS

“…1). In our preceding analysis, we simply rejected events coming from the field-of-view affected by moving structures [3]. We have recently developed moving filter algorithms to reject time-varying portions of our fieldof-view by taking account of moving structures, whose operational data are supplied by JAXA, operating the 'Kibo' module, in order to maximize our exposure for cosmic gamma rays.…”

“…The main target of CALET is observation of high-energy cosmic rays, especially electrons, in the energy range from ∼ 1 GeV to tens of TeV, but its fine detector structure allows us to observe high-energy gamma-rays from ∼ 1 GeV to ∼ 10 TeV. Details of our analysis to extract gamma-ray candidates are described in [2,3]. Here we just mention that we have two trigger modes of the CALET/CAL (calorimeter, the main instrument of CALET) related to gamma-ray observation: a high-energy (HE) mode with an energy threshold ∼ 10 GeV used in normal operation irrespective of geomagnetic latitude, and a low-energy gamma-ray (LE-γ) mode with a threshold ∼ 1 GeV, activated when the geomagnetic latitude is below 20 • and following a CALET Gamma-ray Burst Monitor (CGBM) burst trigger (see [4] for details on our trigger scheme).…”

CALET Upper Limits on GeV-energy Gamma-Ray Burst Emission

“…A dedicated lowenergy gamma (LE-γ) trigger [13] is active at low magnetic latitudes (except for passage through the South Atlantic Anomaly) to reduce the low-energy threshold to approximately 1 GeV. The instrument performance for gamma-ray identification and reconstruction using the LE-γ trigger has been optimized and characterized in detail [14]. The reconstruction of HE photon events is characterized in the same study, but optimization of the charge selection is still in progress and performance is expected to improve.…”

“…One complication arising from observing on the ISS is the obscuration of the field-of-view by external structures. A description of these complications and the background induced is described in detail in [14]. As of writing, the characterization of the moving ISS structures is improved, allowing for an increased exposure available for the analysis of photon events.…”

“…CALET-CAL GRB Observations Nicholas Cannady : Effective area and angular resolution for CAL gamma-ray reconstruction [14]. CC Track and EM Track are algorithms used for the LE-γ and HE trigger events, respectively.…”