Neupert Effect: A Statistical Analysis of M and X-Class Flares During Cycle 24

Abstract

The Neupert effect empirically states that, for many solar flares, the soft X-ray (SXR) time derivative nearly fits the hard X-ray (HXR) or microwave time profiles. This simple relationship supports flare models in which the HXR emission originates by non-thermal bremsstrahlung of accelerated electrons as they gradually lose their energy in the lower corona and chromosphere, while the SXR emission is due to thermal bremsstrahlung from plasma heated by the same electrons. We analyse this effect for the most energetic flares (classified as M or X) during Solar Cycle 24, using SXR observations and microwave data (MW). We assume that the energetic electrons responsible for the HXR emission at chromospheric levels are the same as those that, at low corona levels, produce MW radiation by gyrosynchrotron emission. We observe for the first time that, at MW frequencies registered by the Radio Solar Network Telescopes, the Neupert effect works slightly better between 5 GHz and 9 GHz.