%0 Journal Article
%A Liu, Terry Z.
%A Angelopoulos, Vassilis
%A Lu, San
%T Relativistic electrons generated at Earthâ€™s quasi-parallel bow shock
%D 2019
%R 10.1126/sciadv.aaw1368
%J Science Advances
%P eaaw1368
%V 5
%N 7
%X Plasma shocks are the primary means of accelerating electrons in planetary and astrophysical settings throughout the universe. Which category of shocks, quasi-perpendicular or quasi-parallel, accelerates electrons more efficiently is debated. Although quasi-perpendicular shocks are thought to be more efficient electron accelerators, relativistic electron energies recently observed at quasi-parallel shocks exceed theoretical expectations. Using in situ observations at Earthâ€™s bow shock, we show that such relativistic electrons are generated by the interaction between the quasi-parallel shock and a related nonlinear structure, a foreshock transient, through two betatron accelerations. Our observations show that foreshock transients, overlooked previously, can increase electron acceleration efficiency at a quasi-parallel shock by an order of magnitude. Thus, quasi-parallel shocks could be more important in generating relativistic electrons, such as cosmic ray electrons, than previously thought.
%U https://advances.sciencemag.org/content/advances/5/7/eaaw1368.full.pdf