# Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations

## TL;DR

This study uses non-LTE inversions of SST and IRIS observations to analyze Ellerman bombs and UV bursts, revealing detailed temperature, velocity, and magnetic field structures, and highlighting challenges in modeling Si IV emission accurately.

## Contribution

It introduces a comprehensive non-LTE inversion approach combining multiple spectral lines to characterize transient reconnection events in the solar lower atmosphere.

## Key findings

- Temperature enhancements of up to 15,000 K near the temperature minimum.
- Bi-directional jet signatures observed in velocity maps.
- Magnetic field enhancements co-located with brightenings.

## Abstract

Ellerman bombs and UV bursts are transient brightenings that are ubiquitously observed in the lower atmospheres of active and emerging flux regions. Here we present inversion results of SST/CRISP and CHROMIS, as well as IRIS data of such transient events. Combining information from the Mg II h & k, Si IV and Ca II 8542A and Ca II H & K lines, we aim to characterise their temperature and velocity stratification, as well as their magnetic field configuration. We find average temperature enhancements of a few thousand kelvin close to the classical temperature minimum, but localised peak temperatures of up to 10,000-15,000 K from Ca II inversions. Including Mg II generally dampens these temperature enhancements to below 8000 K, while Si IV requires temperatures in excess of 10,000 K at low heights, but may also be reproduced with secondary temperature enhancements of 35,000-60,000 K higher up. However, reproducing Si IV comes at the expense of overestimating the Mg II emission. The line-of-sight velocity maps show clear bi-directional jet signatures and strong correlation with substructure in the intensity images, with slightly larger velocities towards the observer than away. The magnetic field parameters show an enhancement of the horizontal field co-located with the brightenings at similar heights as the temperature increase. We are thus able to largely reproduce the observational properties of Ellerman bombs with UV burst signature with temperature stratifications peaking close to the classical temperature minimum. Correctly modelling the Si IV emission in agreement with all other diagnostics is, however, an outstanding issue. Accounting for resolution differences, fitting localised temperature enhancements and/or performing spatially-coupled inversions is likely necessary to obtain better agreement between all considered diagnostics.