Heating of the solar photosphere during a white-light flare

Abstract

Context. The Fe I lines observed by the Hinode/SOT spectropolarimeter were always seen in absorption, apart from the extreme solar limb. Here we analyse a unique dataset capturing these lines in emission during a solar white-light flare. Aims. We analyse the temperature stratification in the solar photosphere during a white-light flare and compare it with the post-white-light flare state. Methods. We used two scans of the Hinode/SOT spectropolarimeter to infer, by means of the LTE inversion code Stokes Inversion based on Response function (SIR), the physical properties in the solar photosphere during and after a white-light flare. The resulting model atmospheres are compared and the changes are related to the white-light flare. Results. We show that the analysed white-light flare continuum brightening is probably not caused by the temperature increase at the formation height of the photospheric continuum. However, the photosphere is heated by the flare approximately down to log τ = -0.5 and this results in emission profiles of the observed Fe I lines. From the comparison with the post-white-light flare state of the atmosphere, we estimate that the major contribution to the increase in the continuum intensity originates in the heated chromosphere.