Statistical analysis of first-order anisotropy in multi-spacecraft solar energetic particle events of the solar cycle 25

Solar energetic particles (SEPs) are high-energy charged particles associated with solar eruptions. They constitute a major component of the heliospheric radiation environment, presenting a key space weather hazard. SEPs are accelerated at solar flares and at shock waves driven by coronal mass ejections, but the relative importance of these sources is not fully understood — particularly in the case of electrons. In addition to the underlying acceleration mechanisms, the evolution of a SEP event is highly influenced by transport in the interplanetary space. Anisotropy of the intensity-pitch-angle distribution is an important quantity that can be used to infer information about these effects, especially when multi-spacecraft observations are available. We investigate the first-order anisotropy of electrons and protons in SEP events of the solar cycle 25 using observations from multiple spacecraft of the inner-heliospheric fleet. We pay special attention to the methodology of determining anisotropy and its uncertainty from four-sector telescope (SOLO EPD/EPT and STEREO SEPT) measurements, in which pitch-angle coverage of the telescopes significantly influences the observed anisotropy. We present our methodology and the preliminary results of our statistical analysis, where we study the peaks and durations of anisotropic periods in high-energy electron and proton events as a function of particle energy and longitudinal separation.