Geometry Diagnostics of a Stellar Flare from Fluorescent Xrays.pdfVIP

Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays 1 2 2 3,4 Paola Testa , Jeremy J. Drake , Barbara Ercolano , Fabio Reale , David P. 1 3,4 4 2,5 Huenemoerder , Laura Affer , Giuseppina Micela , David Garcia-Alvarez ABSTRACT 8 0 0 We present evidence of Fe fluorescent emission in the Chandra hetgs spec- 2 trum of the single G-type giant HR 9024 during a large flare. In analogy to solar n a X-ray observations, we interpret the observed Fe Kα line as being produced by J illumination of the photosphere by ionizing coronal X-rays, in which case, for 4 2 a given Fe photospheric abundance, its intensity depends on the height of the ] X-ray source. The hetgs observations, together with 3D Monte Carlo calcula- h tions to model the fluorescence emission, are used to obtain a direct geometric p - constraint on the scale height of the flaring coronal plasma. We compute the Fe o r fluorescent emission induced by the emission of a single flaring coronal loop which t s well reproduces the observed X-ray temporal and spectral properties according a [ to a detailed hydrodynamic modeling. The predicted Fe fluorescent emission is 1 in good agreement with the observed value within observational uncertainties, v pointing to a scale height 0.3R . Comparison of the HR 9024 flare with that 7 ⋆ 5 recently observed on II Peg by Swift indicates the latter is consistent with e