Formation of the delayed relativistic solar electrons

The existence of non-thermal electrons in the solar atmosphere and along the heliospheric field lines is deduced through emission of electromagnetic waves and via direct in situ measurements at 1 AU. The relation between the in situ electrons, their spectral shapes and the relative timing with respect to imaging and spectrographic observations are important in identifying potential acceleration sites and in understanding of the processes which control the formation of the delayed, (mildly) relativistic electrons which are observed in conjunction with flares or coronal mass ejections (CMEs). In contrast to previously suggested paradigms of acceleration of relativistic electrons around the CME shocks or at the flare site, it is suggested here that the delayed acceleration occurs along the stretched, closed coronal field lines, when an anisotropic seed population of low-energy electrons is injected in conjunction with the high frequency coronal radio bursts behind the large CME, as recorded by radioheliographs. The energization proceeds as a bootstrap process due to interaction with oblique whistler waves. The flare serves mainly as a time reference for the electromagnetic emissions, while the propagating CME subsequently opens an access for the relativistic electrons to the interplanetary medium.