The calm before the storm: High spatial resolution mosaic of active region NOAA 14274 at the onset of an X1.2 flare

TL;DR

This paper presents high-resolution solar observations of active region NOAA 14274 just before an X1.2 flare, revealing complex magnetic activity and small-scale brightenings that precede major solar eruptions.

Contribution

It provides the first large mosaic of speckle-restored images from the GREGOR telescope capturing pre-flare activity at high resolution.

Findings

Active region showed curved penumbral filaments and sunspot rotation.

Magnetic field was highly stressed, leading to multiple flares.

Small-scale brightenings preceded the X1.2 flare.

Abstract

Active region NOAA 14274 produced some of the strongest flares of Solar Cycle 25, including the X1.2 and X5.1 flares on 10 and 11 November 2025, respectively. We present the first large mosaic of speckle-restored images obtained with the improved High-resolution Fast Imager (HiFI+) at the 1.5-meter GREGOR solar telescope at the Observatorio del Teide in Iza\~na, Tenerife, Spain. The observations were obtained approximately 30 minutes before the onset of the X1.2 flare. The active region exhibited strongly curved penumbral filaments, sunspot rotation, and shear motions along the polarity inversion line (PIL), which led to a highly stressed magnetic field configuration that stored sufficient energy to release multiple M- and X-class flares. The first flare signatures appeared as small-scale brightenings, each with a width of a few tenths of an arcsecond, that trace penumbral filaments in the trailing sunspot.