An energetic pre-flare

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Revision as of 09:56, 12 February 2019

Introduction

How much energy is released in a flare? Which fractions of this energy are converted into accelerated particles and hot plasma, respectively. RHESSI observations have been used to answer these questions in many different ways - add a few references here - . While RHESSI observations have considerably improved our understanding of flare energetics, they have a limitation. Due to the typically steep power-law shape of the accelerated electron spectrum, the total energy is dominated by low energetic electrons, whose signatures are found at photon energies for which the interpretation of the spectrum can be ambiguous and/or to which RHESSI is not sensitive (Kontar et al. 2011, for a review). One way to overcome this, is to include data from SDO/AIA. This way, the lower energies are much better constrained. We used this method to analyze the pre-impulsive phase of the well known event SOL2012-07-19T05:58. Up to 20 minutes before the impulsive phase, two X-ray sources could be imaged, one below and one above what was interpreted as the magnetic reconnection region.

Simultaenous fitting of RHESSI and AIA data

This idea of this method, developed by Motorina & Kontar 2015 [1] is that any mean electron flux distribution can be described via a differential emission measure Failed to parse (PNG conversion failed; check for correct installation of latex, dvips, gs, and convert): $\xi(T)$:

Failed to parse (PNG conversion failed; check for correct installation of latex, dvips, gs, and convert): \langle nVF(E)\rangle=\frac{2^{3/2}E}{(\pi m_e)^{1/2}}\int_0^\infty \frac{\xi(T)}{(k_BT)^{3/2}}\exp(-E/(k_BT))dT,\, \;\;\;\mathrm{[electrons\,keV^{-1}s^{-1}cm^{-2}]}

And any observed count spectrum can be forward fitted with such a model. Hence, RHESSI and AIA data are combined into one dataset and a single temperature response matrix is computed. This combined data set is then forward fitted with a model DEM of the shape:

This is not any DEM but it can be shown that it actually represents the kappa-distribution.

The pre-impulsive phase of SOL2012-07-19T05:58

Conclusion