Observations of magnetic reconnection in the deep solar atmosphere in the Hε line

Abstract

Context. Magnetic reconnection in the deep solar atmosphere can give rise to enhanced emission in the Balmer hydrogen lines, a phenomenon known as Ellerman bombs (EBs). It is most common to observe EBs in the Hα and Hβ spectral lines. High-quality shorter-wavelength Balmer line observations of EBs are rare, but have the potential to provide the most highly resolved view on magnetic reconnection. Aims. We aim to evaluate the Hε 3970 Å line as an EB diagnostic by analyzing high-quality observations in different Balmer lines. Methods. Observations of different targets and viewing angles were acquired with the Swedish 1-m Solar Telescope. These observations sample EBs in different environments: active regions, the quiet Sun, and the penumbra and moat of a sunspot. We employed an automated detection method for quiet-Sun EBs based on k-means clustering. Results. Ellerman bombs in the Hε line show similar characteristics as in the longer-wavelength Balmer lines: a higher intensity than in the surroundings, rapid variability, and a flame-like morphology. In a 24 min quiet-Sun time series, we detected 1674 EBs in the Hε line. This is 1.7 times more EBs than in Hβ. The quiet-Sun EBs measured in Hε are very similar to those in Hβ: They have similar lifetimes and a similar area, brightness, and spatial distribution. Most of the EBs detected in Hε are closer to the limb than their Hβ counterparts because the Hε line core EB emission is formed higher in the atmosphere than the Hβ EB wing emission. Conclusions. We conclude that the Hε line is well suited for studying EBs, and consequently, for measuring the dynamics of magnetic reconnection in the solar atmosphere at the smallest scales. Our findings suggests that the deep atmosphere in the quiet Sun may host more than 750 000 reconnection events with an EB signature at any time. This is significantly more than what was found in earlier Hβ observations.