Helios SEP Events Catalog

It is not the first time that data from this historical mission are included in a statistical study. In Lario et al., 2006 (https://doi.org/10.1086/508982) some events observed by two or more spacecraft were analyzed from the point of view of their longitudinal and radial spread. The events where protons with energies above 13 MeV were observed by the Helios spacecraft when they were located at less than ~0.85 AU from the Sun were in the focus of the ESA SOL2UP project (for details see Pacheco, 2019, PhD Thesis, http://hdl.handle.net/10803/667033). The events from our catalogue which overlap with these previous studies are marked by letters L or P, correspondingly. At the same time, the data related to the overlapping events (same as for all other events), either characterizing the solar source, location of the observer (spacecraft) or relating to the properties of the particle fluxes were identified independently for the present catalogue. Nevertheless, we would like to acknowledge the authors of the previous SOL2UP project for providing us with the results of their studies.

In the majority of the cases the identification of the location of the solar source was based on the available X-ray data of the related solar flare, published in (Solar Geophysical Data). In addition, we used information from a previous study of Helios events (Kallenrode 1997, private communication), marked with the “K” sign. The radial distance of the spacecraft from the Sun, the solar wind speed and the Earth-Sun-spacecraft angle were taken from (CDAweb). If there were no data for the solar wind speed during the time of the event, a standard value of 400 km/s was used (in the list itself and in the calculation of the longitude of the magnetic footpoint of the spacecraft). If there was, e.g., a high speed stream of the solar wind close to the time of the event then the average value of the solar wind stream was used. In both cases we used the “~” sign to denote such uncertainties. The location of the footpoint of the spacecraft of the solar disc was obtained by using a simple ballistic back mapping. The proton onset times are based on the SEPServer data.