Dips and Waves

From RHESSI Wiki

Introduction

There has been some heated discussion as to whether the "dip" seen in the mean electron spectrum derived from RHESSI flare observations is a real feature as it can often be removed be correcting for albedo. But for flares with relatively low thermal mission the standard "thick-target" interpretation says that the "dip" must be there. This model only accounts for Coulomb collisions between the propagating beam of accelerated electrons and the background plasma. In this nugget we present simulation results from our recent paper [1] where we show what happens to the dip when you also include wave-particle interactions between the beam and background plasma.

Wave-particle Interactions

In the standard interpretation of RHESSI's hard x-ray emission, a powerlaw of acceelerated electrons above a sharp low energy cutoff leave the corona travelling down to the chromosphere. As they propagate they lose energy to the background plasma through Coloumb collisions, eventually losing their energy in the dense chromosphere, where they emit hard X-rays as observed by RHESSI, heating the local plasma which expands back upwards.

Conclusions

The work shown here is a step towards a more complete treatment of electron transport in solar flares and highlights that the inclusion of wave-particle interactions flattens sharp low energy cutoffs in the inital accelerated electron distribution.