Abstract | Energetic electrons are accelerated during solar flares, and produce bremsstrahlung emission in the X-ray domain as they propagate in the low corona towards denser regions and interact with the ambient medium. One challenge of high energy solar physics is to determine the link between X-ray observations (with RHESSI) and the physical processes of particle acceleration and propagation in the corona.
For the 2004, May 21 solar flare, we show that the number of energetic electrons in the coronal part of the flaring loop exceeds the number of electrons needed to explain the hard X-ray emission from the footpoints of the same loop. Such observation cannot be explained by the standard collisional transport model: an additional physical process is needed to explain how energetic electrons can be trapped in the corona.
In the hypothesis of turbulent pitch-angle scattering of energetic electrons (Kontar et al, 2014), diffusive transport can lead to a confinement of energetic electrons in the coronal source. We estimated the mean-free path of energetic electrons in this particular event to $10^{8}$ – $10^{9}$ meters, which is smaller than the size of the flaring loop itself, and thus implies an efficient turbulent trapping. These observations are in agreement with a previous study of the gyrosynchrotron emission of this event (Kuznetsov & Kontar, 2015).
References:
Kontar, E.P. et al. (2014; ApJ, 780, 176)
Kuznetsov, A.A. & Kontar, E.P. (2015 ; SoPh, 290, 79)
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