Impulsivity Parameter for Solar Flares

Abstract:

Typically three phases are observed during solar flares: the preflare, impulsive and decay phases. During the impulsive phase it is believed that the electrons and other particles are accelerated after the stored energy in the magnetic field is released by reconnection. The impulsivity of a solar flare is a quantifiable property which shows how fast occur this initial energy release. It is measured via the impulsivity parameter which we define as the inverse of the overall duration of the impulsive phase. We take the latter as the raw width of the most prominent non-thermal emission of the flare. We computed this observable over a work sample of 48 M class events occurred during the present Solar Cycle 24 by using three different methods. The first method takes into account all the non-thermal flare emission and gives very accurate results, while the other two just cover fixed energy intervals (30-40 keV and 25-50 keV) and are useful for fast calculations. We propose an alternative way to classify solar flares according to their impulsivity parameter values, defining three different types of impulsivity, namely: high, normal and low. This system of classification is independent of the manner used to calculated the impulsivity parameter. Lastly, we show the relevance of this tool as a discriminator of different HXR generation processes.