Depth of Ellerman burst derived from high-resolution H and Ca II 8542 spectra

High-resolution spectra of an Ellerman burst (EB) sampling the H and the Ca ii 8542 lines obtained with the Fast Imaging Solar Spectrograph (FISS) installed on the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory are compared with synthetic line profiles constructed using the RH code for nonlocal thermodynamical equilibrium radiative transfer. The EB heating is modeled by a local temperature hump above the quiet-Sun temperature. Our first finding is that FISS H and Ca ii 8542 intensity profiles cannot be reproduced simultaneously by a single hump model as far as the hump is thicker than ≥100 km. Simultaneous reproduction of both line profiles is possible when the EB temperature enhancement is confined to a layer as thin as ≤20 km in the photosphere where the H wing response is high and that of the Ca ii 8542 is not. Moreover, when we examine the EB spectra at different times, we find that the EB at a time of weaker appearance is located at lower heights, ∼50 km, and moves upward to ∼120 km at the time of maximum intensity. Complementary calculations of the Na i D ₁ and Mg I b ₂ lines as well as that of UV continuum at 1600 and 1700 with the deduced EB atmosphere are also performed to test the result, which allows us to discuss the shortcomings of this plane-parallel static model atmosphere for understanding the physical properties of EBs.