Energy spectra of 300 keV to 1 MeV electrons from the SOHO Electron Proton Helium INstrument (EPHIN)

The origins of energetic electrons with energies ranging from a few tens of keV to tens of MeV in the inner heliosphere are manifold. They include Galactic Cosmic Rays, Jovian electrons as well as sporadic Solar Energetic Electron (SEE) events. Their energy spectra provide insights into the acceleration at the source and transport processes in the heliosphere.

The SOlar and Heliospheric Observatory (SOHO) was launched in December 1995 with the Electron Proton Helium INstrument (EPHIN) measuring electrons from 150 keV to several MeV. However, its measuring capability was reduced due to the loss of two detectors in 1997 and 2017, respectively. Thus from 2017 onwards only two electron channels, one in the range from 300 keV to one MeV and one “integral channel” that measures between 300 keV and 10 MeV.

In this contribution we present a new data product for electron spectra based on the onboard histograms. This data product has the advantage of providing the total energy loss in the first two detectors with good statistics compromising energy loss determination via PHA data and counting statistics of the single channel. Using the so-called bow-tie method we were able to derive several energy channels between 300 keV and about 1 MeV. We present first results and compare them with instruments from other missions.

The SOHO/EPHIN project is supported under Grant 50 OC 2102 by the German Bundesministerium für Wirtschaft through the Deutsches Zentrum für Luft- und Raumfahrt (DLR). This study has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004159 (SERPENTINE).