Solar origin of in-situ near-relativistic electron spikes observed with SEPT/STEREO

Abstract

During 2010-2011 the Solar Electron Proton Telescope (SEPT) onboard the twin STEREO spacecraft detected a number of typical impulsive electron events showing a prompt intensity onset followed by a long decay, as well as several near-relativistic so-called electron spike events. These spikes are characterized by a very short duration of below 10-20 min at FWHM, almost symmetric time profiles, velocity dispersion and strong anisotropy, revealing a very weak scattering during particle propagation from the Sun to STEREO. Spikes are detected at energies below 300 keV and appear simulateneously with type III radio bursts detected by SWAVES/STEREO and narrow EUV jets in active regions. Using particle, EUV and radio imaging observations we found that nearrelativistic electrons were accelerated simultaneously and at the same location as the electrons emitting the accompanying type III radio bursts and together with coronal EUV jets. Furthermore, the sources of type III radio bursts match very well the locations and the trajectories of the associated EUV jet. Applying a particle propagation model we demonstrate that the spike characteristics reflect both, properties of the accelerator and effects of interplanetary propagation.

A tiny event producing an interplanetary type III burst

“…This is also supported by the in situ detection of electron spikes at energies below 300 keV (Klassen et al 2011(Klassen et al , 2012, whose timing is well correlated with type III bursts and EUV jets. For jet events correlated with both type III bursts and electron events observed in situ, the flare geometry can be explained by reconnection between open and closed magnetic field lines (the so-called interchange reconnection; Krucker et al 2011).…”

“…Type III radio bursts are known to be associated not only with flares, but also with Hα ejecta (Axisa et al 1973), X-ray bright points (Kundu et al 1994(Kundu et al , 1995a, soft X-ray transient brightenings (Nindos et al 1999), and soft X-ray or/and extreme-UV (EUV) jets (Kundu et al 1995b;Raulin et al 1996;Pick et al 2006;Nitta et al 2008;Innes et al 2011;Krucker et al 2011;Klassen et al 2011Klassen et al , 2012Chen et al 2013a,b). Jets that are correlated with type III bursts accompany flaring activity that ranges from weak transient brightenings and subflares (Kundu et al 1995b;Raulin et al 1996;Nitta et al 2008) to M-class flares (Krucker et al 2011;Chen et al 2013a).…”

Unexpected spatial intensity distributions and onset timing of solar electron events observed by closely spaced STEREO spacecraft

“…Therefore a nonradial electron injection pattern could play an important role in building up the unexpected intensity distribution. Such nonradial electron injection is often observed by tracing of type III radio bursts showing non-radial trajectories and positions relative to the parent flare (e.g., Klassen et al 1999Klassen et al , 2012. The same is valid for type II radio bursts and coronal shocks, which sometimes show a non-radial/azimuthal propagation trajectory in the corona (Aurass et al 1998).…”

A review of solar type III radio bursts

“…The observed correlation between the spectral indices of energetic electrons at the Sun from X-ray data and the Earth from in-situ data (Lin, 1985;Krucker et al, 2007) is often viewed as an additional support for scatter-free transport. However, the injection time of energetic electrons at different energies does not correspond to the inferred injection time by looking at the associated type III bursts (Krucker et al, 1999;Haggerty & Roelof, 2002;Cane, 2003;Wang et al, 2006Wang et al, , 2011Kahler et al, 2011;Klassen et al, 2012). Low energy electrons (e.g.…”