Diagnostics of Ellerman Bombs with High-resolution Spectral Data

Ellerman bombs (EBs) are tiny brightenings often observed near sunspots. The most impressive characteristic of the EB spectra is the two emission bumps in both wings of the H$\alpha$ and \ion{Ca}{II} 8542 {\AA} lines. High-resolution spectral data of three small EBs were obtained on 2013 June 6 with the largest solar telescope, the 1.6 meter New Solar Telescope (NST), at the Big Bear Solar Observatory. The characteristics of these EBs are analyzed. The sizes of the EBs are in the range of 0.3\arcsec\--0.8\arcsec\ and their durations are only 3--5 minutes. Our semi-empirical atmospheric models indicate that the heating occurs around the temperature minimum region with a temperature increase of 2700--3000 K, which is surprisingly higher than previously thought. The radiative and kinetic energies are estimated to be as high as 5$\times$10$^{25}$--3.0$\times$10$^{26}$ ergs despite the small size of these EBs. Observations of the magnetic field show that the EBs appeared just in a parasitic region with mixed polarities and accompanied by mass motions. Nonlinear force-free field extrapolation reveals that the three EBs are connected with a series of magnetic field lines associated with bald patches, which strongly implies that these EBs should be produced by magnetic reconnection in the solar lower atmosphere. According to the lightcurves and the estimated magnetic reconnection rate, we propose that there is a three phase process in EBs: pre-heating, flaring and cooling phases.