[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P21] Calibration for Arase HEP-L cross-channel contamination and comparison of Arase electron pitch angle distributions with Van Allen Probes

*Milla Kalliokoski¹、Kazushi Asamura¹、Iku Shinohara¹、Takefumi Mitani¹、Tomoaki Hori²、Yoshizumi Miyoshi²、Nana Higashio¹、Takeshi Takashima¹ (1.JAXA ISAS、2.ISEE, Nagoya University)

キーワード：Earth, radiation belt, electrons, Arase

Arase observes electron fluxes over a wide energy range from a few electronvolts to several MeV in the Earth’s radiation belts, similarly to the Van Allen Probes. While the omnidirectional fluxes between these satellites have previously been compared, they offer a limited view of the radiation belt dynamics. We compared the pitch angle distributions (PADs) from Arase and Van Allen Probes during close conjunctions for a more detailed comparison, since for example wave-particle interactions can depend on the pitch angle. Here we derived PADs from high-energy electron experiment (HEP-L) and extremely high-energy experiment (XEP) on Arase, and the Magnetic Electron Ion Spectrometer (MagEIS) and the Relativistic Electron-Proton Telescope (REPT) instruments on Van Allen Probes. There is a remarkable agreement within a factor of 2 for all energies, for all pitch angles for XEP data and for most pitch angles (20 to 160 degrees) for HEP-L data. The discrepancy at the field-aligned pitch angles is significantly reduced by applying an additional correction for HEP-L data to reduce cross-channel contamination. HEP-L is a state-of-the-art instrument measuring electrons from 60 keV to 1.5 MeV and can distinguish the incoming direction of electrons by position sensitive detectors, thus accurately determining the pitch angle. HEP-L data has been previously extensively calibrated based on the modeled response functions of the instrument’s energy channels using Geant4 simulation. Utilizing the same simulation, we have now considered the calibration in terms of the azimuthal channels, i.e., the direction of measured counts. As shown by the simulation, the distribution of counts in each azimuthal channel is broader than the nominal range in the initial direction angle, causing the cross-channel contamination that has the biggest effect at field-aligned pitch angles. We derive correction factors from the simulation separately for each energy channel and apply it to HEP-L measurements, and the comparison of PADs calculated with the corrected HEP-L data to PADs from Van Allen Probes confirms the improvement.