Electron Density Measurement at the Loop-Top Region of the 2017 September 10 Solar Limb Flare

Jej\v{c}i\v{c} et al. (2018) have reported high-density plasmas at the loop-top region of the SOL2017-09-10 X8.2 limb flare from the analysis of the continuum flux observed with the SDO/HMI. The reported electron density is about $10^{13} ~\mbox{cm}^{-3}$, which is extraordinary high to the commonly reported values. We have estimated the electron density of loop-top regions of the flare loops in the cooling phase by the density-sensitive Fe XII line pairs that were observed with the Hinode EUV imaging spectrometer (EIS). The height of the cooling loops we analyzed is lower than the scale height of the line formation temperature of the Fe XII lines. The line ratio from the CHIANTI model spectra has a high-density limit that appears near $1\times 10^{12} ~\mbox{cm}^{-3}$. While the observed line ratios after the standard calibration by the SSW analysis software show reasonable coronal values in the same region at the preflare timing, the ratios just after the peak phase of the flare largely exceed the limit value from the model, also suggesting extremely high electron density in the cooling loops at least. The large values of the observed line ratio are found at the higher edge of the cooling loops. To understand the relationships between observed and model ratios, we will report an additional study of the EIS sensitivity calibration.