Electrons in GEO Measured With the ESA Multifunctional Spectrometer During the January 2014 SEP

The multifunctional spectrometer (MFS) is a radiation monitor installed on the X panel of the Alphasat satellite, in geostationary orbit (GEO) since July 2013. The MFS was specially tailored to characterize the space radiation environment in GEO and it is expected to acquire scientific data during a total lifetime of five years. An end-to-end Geant4 simulation of the MFS flight model based on the full geometry of the MFS, imported from computer-aided design (CAD) to geometry description markup language, was implemented and validated with the MFS ground-test results obtained in Paul Scherrer Institute facilities in 2010. The MFS simulation was then used to derive response functions for the MFS electron and proton channels. This paper describes the implementation of a maximum likelihood fit method to reconstruct particle spectra from MFS data, and its application to the reconstruction of the electron spectra for a 20-day period centered on the occurrence of January 2, 2014, solar energetic particle event. The obtained electron integral fluxes for this period are in reasonable agreement with GOES-15 public data and with the predictions of the AE8MIN update and IGE-2006 models.