The Specific Acceleration Rate in Loopstructured Solar Flares  Implications for Electron Acceleration Models 

Jingnan Guo Submitted: 20130306 01:42
We analyze electron flux maps based on RHESSI hard Xray imaging spectroscopy data for a number of extended coronal loop flare events. For each event, we determine the variation of the characteristic loop length L with electron energy E, and we fit this observed behavior with models that incorporate an extended acceleration region and an exterior ''propagation'' region, and which may include collisional modification of the accelerated electron spectrum inside the acceleration region. The models are characterized by two parameters: the plasma density n in, and the longitudinal extent L_{0} of, the acceleration region. Determination of the bestfit values of these parameters permits inference of the volume that encompasses the acceleration region and of the total number of particles within it. It is then straightforward to compute values for the emission filling factor and for the specific acceleration rate (electrons per second per ambient electron above a chosen reference energy). For the 24 events studied, the range of inferred filling factors is consistent with a value of unity. The inferred mean value of the specific acceleration rate above E_0=20 keV is sim10^{2} s^{1}, with a 1sigma spread of about a halforderofmagnitude above and below this value. We compare these values with the predictions of several models, including acceleration by largescale, weak (subDreicer) fields, by strong (superDreicer) electric fields in a reconnecting current sheet, and by stochastic acceleration processes.
Authors: Jingnan Guo, A. Gordon Emslie, Michele Piana
Projects: RHESSI

Publication Status: ApJ, 2013, 766, 28
Last Modified: 20130308 08:49


