# The second flight of the SUNRISE balloon-borne solar observatory: overview of instrument updates, the flight, the data and first results

## TL;DR

The SUNRISE balloon observatory's second flight provided high-resolution solar images, including the first in Mg II k, with improved instruments and data analysis, revealing detailed magnetic and thermal properties of active regions.

## Contribution

This paper reports on the second flight of SUNRISE, highlighting instrument upgrades, new high-resolution Mg II k imaging, and advanced data reduction techniques, including polarimetric inversion methods.

## Key findings

- High-resolution Mg II k images achieved at diffraction limit
- Magnetic fields in pores reach up to 2500 G
- Small pores can have temperatures comparable to quiet Sun

## Abstract

The SUNRISE balloon-borne solar observatory, consisting of a 1~m aperture telescope that provided a stabilized image to a UV filter imager and an imaging vector polarimeter, carried out its second science flight in June 2013. It provided observations of parts of active regions at high spatial resolution, including the first high-resolution images in the Mg~{\sc ii}~k line. The obtained data are of very high quality, with the best UV images reaching the diffraction limit of the telescope at 3000~\AA\ after Multi-Frame Blind Deconvolution reconstruction accounting for phase-diversity information. Here a brief update is given of the instruments and the data reduction techniques, which includes an inversion of the polarimetric data. Mainly those aspects that evolved compared with the first flight are described. A tabular overview of the observations is given. In addition, an example time series of a part of the emerging active region NOAA AR~11768 observed relatively close to disk centre is described and discussed in some detail. The observations cover the pores in the trailing polarity of the active region, as well as the polarity inversion line where flux emergence was ongoing and a small flare-like brightening occurred in the course of the time series. The pores are found to contain magnetic field strengths ranging up to 2500~G and, while large pores are clearly darker and cooler than the quiet Sun in all layers of the photosphere, the temperature and brightness of small pores approach or even exceed those of the quiet Sun in the upper photosphere.