Before the onset of a flare is observed in hard X-rays there is often aprolonged pre-flare or pre-heating phase with no detectable hard X-ray emissionbut pronounced soft X-ray emission suggesting that energy is being released anddeposited into the corona and chromosphere already at this stage. This workanalyses the temporal evolution of coronal source heating and the chromosphericresponse during this pre-heating phase to investigate the origin and nature ofearly energy release and transport during a solar flare. Simultaneous X-ray,EUV, and microwave observations of a well observed flare with a prolongedpre-heating phase are analysed to study the time evolution of the thermalemission and to determine the onset of particle acceleration. During the 20minutes duration of the pre-heating phase we find no hint of acceleratedelectrons, neither in hard X-rays nor in microwave emission. However, the totalenergy budget during the pre-heating phase suggests that energy must besupplied to the flaring loop to sustain the observed temperature and emissionmeasure. Under the assumption of this energy being transported toward thechromosphere via thermal conduction, significant energy deposition at thechromosphere is expected. However, no detectable increase of the emission inthe AIA wavelength channels sensitive to chromospheric temperatures isobserved. The observations suggest energy release and deposition in the flaringloop before the onset of particle acceleration, yet a model in which energy isconducted to the chromosphere and subsequent heating of the chromosphere is notsupported by the observations.
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