2020/04/10 by David R. Graham, Gianna Cauzzi, Luca Zangrilli +3 · 3 citations
Physics and Astronomy · #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/ab88ad
Accepted for publication by the Astrophysical Journal - 9th April 2020
arxiv created 2020/04/10 · arxiv updated 2020/05/27
We study the evolution of chromospheric line and continuum emission during the impulsive phase of the X-class SOL2014-09-10T17:45 solar flare. We extend previous analyses of this flare to multiple chromospheric lines of Fe I, Fe II, Mg II, C I, and Si II, observed with IRIS, combined with radiative-hydrodynamical (RHD) modeling. For multiple flaring kernels, the lines all show a rapidly evolving double-component structure: an enhanced, emission component at rest, and a broad, highly red-shifted component of comparable intensity. The red-shifted components migrate from 25-50 km s-1 towards the rest wavelength within ∼30 seconds. Using Fermi hard X-ray observations, we derive the parameters of an accelerated electron beam impacting the dense chromosphere, using them to drive a RHD simulation with the RADYN code. As in Kowalski et al. 2017a, our simulations show that the most energetic electrons penetrate into the deep chromosphere, heating it to T∼10,000 K, while the bulk of the electrons dissipate their energy higher, driving an explosive evaporation, and its counterpart condensation -- a very dense (ne ∼ 2 × 1014 cm-3), thin layer (30--40 km thickness), heated to 8--12,000 K, moving towards the stationary chromosphere at up to 50 km s-1. The synthetic Fe II 2814.45A profiles closely resemble the observational data, including a continuum enhancement, and both a stationary and a highly red-shifted component, rapidly moving towards the rest wavelength. Importantly, the absolute continuum intensity, ratio of component intensities, relative time of appearance, and red-shift amplitude, are sensitive to the model input parameters, showing great potential as diagnostics.