Efficiency of particle acceleration at interplanetary shocks: Statistical study of STEREO observations

: Dresing N, Theesen S, Klassen A, Heber B

Publisher: EDP SCIENCES S A

: 2016

: Astronomy and Astrophysics

: ASTRONOMY & ASTROPHYSICS

: ASTRON ASTROPHYS

: ARTN A17

: 588

: 10

: 1432-0746

DOI: https://doi.org/10.1051/0004-6361/201527853

Context. Among others, shocks are known to be accelerators of energetic charged particles. However, many questions regarding the acceleration efficiency and the required conditions are not fully understood. In particular, the acceleration of electrons by shocks is often questioned.Aims. In this study we determine the efficiency of interplanetary shocks for <100 keV electrons, and for ions at similar to 0.1 and similar to 2MeV energies, as measured by the Solar Electron and Proton Telescope (SEPT) instruments aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft.Methods. We employ an online STEREO in situ shock catalog that lists all shocks observed between 2007 and mid 2014 (observed by STEREO A) and until end of 2013 (observed by STEREO B). In total 475 shocks are listed. To determine the particle acceleration e ffi ciency of these shocks, we analyze the associated intensity increases (shock spikes) during the shock crossings. For the nearrelativistic electrons, we take into account the issue of possible ion contamination in the SEPT instrument.Results. The highest acceleration e ffi ciency is found for low energy ions (0.1MeV), which show a shock-associated increase at 27% of all shocks. The 2MeV ions show an associated increase only during 5% of the shock crossings. In the case of the electrons, the shocks are nearly ine ff ective. Only five shock-associated electron increases were found, which correspond to only 1% of all shock crossings.