Imaging spectroscopy in X-rays with RHESSI provide the possibility to investigate the spatial evolution of the X-ray emitting electron distribution and therefore to study the transport effects on energetic electrons during solar flares. We study the energy dependence of the energetic electron scattering mean free path in the solar corona. We use the imaging spectroscopy technique with RHESSI to study the evolution of energetic electrons distribution in different part of the magnetic loop during the 2004 May 21 flare. These observations are compared with the radio observations of the gyrosynchrotron radiation of the same flare by Kuznetsov and Kontar (2015), and with the predictions of the diffusive transport model described by Kontar et al. (2014). The X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for the radio-emitting electrons than for the X-ray-emitting electrons. These observations can be explained by the diffusive transport model derived by Kontar et al. (2014). We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron transport in the solar corona in different energy domains. We show that the diffusive transport model can explain our observations; and in the range 25-500 keV, the electron scattering mean free path decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.
Authors: S. Musset, E. P. Kontar and N. Vilmer
Publication Status: Published online
Last Modified: 2018-02-08 16:19
Hard X-ray emitting energetic electrons and photospheric electric currents
The energy released during solar flares is believed to be stored in non-potential magnetic fields associated with electric currents flowing in the corona. While no measurements of coronal electric currents are presently available, maps of photospheric electric currents can now be derived from SDO/HMI observations. Photospheric electric currents have been shown to be the tracers of the coronal electric currents. Particle acceleration can result from electric fields associated with coronal electric currents. We revisit here some aspects of the relationship between particle acceleration in solar flares and electric currents in the active region. We study the relation between the energetic electron interaction sites in the solar atmosphere, and the magnitudes and changes of vertical electric current densities measured at the photospheric level, during the X2.2 flare on February 15 2011 in AR NOAA 11158. X-ray images from RHESSI are overlaid on magnetic field and electric current density maps calculated from the spectropolarimetric measurements of SDO/HMI using the UNNOFIT inversion and Metcalf disambiguation codes. X-ray images are also compared with EUV images from SDO/AIA to complement the flare analysis. Part of the elongated X-ray emissions from both thermal and non-thermal electrons overlay the elongated narrow current ribbons observed at the photospheric level. A new X-ray source at 50-100 keV (produced by non-thermal electrons) is observed in the course of the flare and is cospatial with a region in which new vertical photospheric currents appeared during the same period (increase of 15%). These observational results are discussed in the context of the scenarios in which magnetic reconnection (and subsequent plasma heating and particle acceleration) occurs at current-carrying layers in the corona.
Authors: Sophie Musset, Nicole Vilmer, Véronique Bommier
Publication Status: accepted
Last Modified: 2015-07-10 20:37