Main Objective: The main objective is to investigate the energetics and the effects of the precipitating electrons from the corona toward the lower solar atmosphere during solar flares, by combining spectral measurements through the IR, visible, UV and X-rays. We would like to request co-observations of IRIS and Hinode during our campaign of joint observations between GREGOR and STIX onboard Solar Orbiter.
Scientific Justification: In the standard flare model, the magnetic reconnection that occurs in the corona releases energy in the form of kinetic energy of particles. Herein, guided by the magnetic field lines, previously accelerated electrons travel toward the solar surface and by interacting with the dense chromosphere via Coulomb collisions, they heat the ambient plasma and trigger the production of the impulsive nonthermal bremsstrahlung emission in Hard X-rays (see Fletcher et al., 2011). Consequently, the heated chromospheric plasma expands upward into the flare loops, through the process known as chromospheric evaporation. This process produces enhanced thermal bremsstrahlung emissions in Soft X-rays and in the standard flare model it manifests as a gradual phase. The delay between the impulsive manifestation and the gradual phase that manifests in this scenario is better known as the Neupert effect.
However, generally, two different processes can lead to the chromospheric evaporation. The first one is related to the precipitating electron beam, which, depending on the power, can be distinguished between explosive and gentle. The second process triggering the chromospheric evaporation is due to the conductive energy flux in the absence of electron beams (Battaglia et al., 2015). Observations of different emission lines forming at different altitudes in the chromosphere, combined with STIX imaging and spectroscopy, are needed for unambiguous distinction between the type of energy input causing the evaporation (electron beam or conductive energy input) and its nature (explosive or gentle). With IRIS and Hinode, the purpose is to have a more complete temperature coverage to unambiguously distinct between chromospheric evaporations. Hence, our observation will focus on measuring the evolution of the flare ribbons.
Finally, spectral measurements through IR, visible, and UV of the proposed campaign, will allow us to investigate also the energetics of flares and the influence on the lower atmosphere. Indeed, the spectral shape and its evolution will allow us to deduce the energy that goes into the radiation and then it will be compared to the input energy of accelerated electrons derived from the STIX X-ray observations. |
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