Soft X-ray heating of the solar chromosphere during the gradual phase of two solar flares

¹ Observatoire de Paris, Section de Meudon, LESIA, 92195 Meudon Principal Cedex, France
² Astronomical Institute of the Wrocław University, ul. Kopernika 11, 51-622 Wrocław, Poland
³ Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondrejov, The Czech Republic

Corresponding author: A. Berlicki, arkadiusz.berlicki@obspm.fr

Received: 13 November 2003
Accepted: 2 February 2004

Abstract

In this paper we perform an analysis of the energetics of the solar flaring chromosphere irradiated by soft X-rays (SXR) emitted from overlying hot flare loops. To study an expected SXR heating we used the observations of two solar flares obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph attached to the Large Coronagraph of the Wrocław University. SXR observations of these flares come from the Yohkoh SXR telescope (SXT). From MSDP spectral images we derived mean Hα line profiles which were then used to construct semi-empirical non-LTE models of the chromosphere in the analyzed areas of flares. On the basis of SXR observations we calculated the mean emission measure EM and the temperature in flaring coronal structures located above the Hα kernels under study and these two quantities were used to compute the SXR irradiation of the chromosphere between 1–300 Å. For each flare model we then evaluated the energy deposit due to such irradiation and compared it with the net radiative cooling rates at all depths in the chromosphere. By means of such modelling we were able to demonstrate that the enhanced emission of selected Hα kernels observed during the gradual phase of these two solar flares cannot be explained in terms of the SXR heating of the chromosphere. We found that radiative losses in all layers of the chromosphere exceeded the amount of the energy deposited by the SXR radiation. However, for stronger flares with much enhanced EM a certain contribution of SXR to the heating cannot be ruled out.