Small-scale magnetic flux emergence preceding a chain of energetic solar atmospheric events

Nóbrega-Siverio, D.; Cabello, I.; Bose, S.; van der Voort, L. H. M. Rouppe; Joshi, R.; Froment, C.; Henriques, V. M. J.
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Astronomy and Astrophysics

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Context. Advancements in instrumentation have revealed a multitude of small-scale extreme-ultraviolet (EUV) events in the solar atmosphere and considerable effort is currently undergoing to unravel them.
Aims: Our aim is to employ high-resolution and high-sensitivity magnetograms to gain a detailed understanding of the magnetic origin of such phenomena.
Methods: We used coordinated observations from the Swedish 1-m Solar Telescope (SST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO) to analyze an ephemeral magnetic flux emergence episode and the following chain of small-scale energetic events. These unique observations clearly link these phenomena together.
Results: The high-resolution (0.″057 pixel−1) magnetograms obtained with SST/CRISP allowed us to reliably measure the magnetic field at the photosphere and to detect the emerging bipole that caused the subsequent eruptive atmospheric events. Notably, this small-scale emergence episode remains indiscernible in the lower resolution SDO/HMI magnetograms (0.″5 pixel−1). We report the appearance of a dark bubble in Ca II K 3933 Å related to the emerging bipole, a sign of the canonical expanding magnetic dome predicted in flux emergence simulations. Evidence of reconnection are also found, first through an Ellerman bomb and later by the launch of a surge next to a UV burst. The UV burst exhibits a weak EUV counterpart in the coronal SDO/AIA channels. By calculating the differential emission measure (DEM), its plasma is shown to reach a temperature beyond 1 MK and to have densities between the upper chromosphere and transition region.
Conclusions: Our study showcases the importance of high-resolution magnetograms in revealing the mechanisms that trigger phenomena such as EBs, UV bursts, and surges. This could hold implications for small-scale events similar to those recently reported in the EUV using Solar Orbiter. The finding of temperatures beyond 1 MK in the UV burst plasma strongly suggests that we are examining analogous features. Therefore, we recommend caution when drawing conclusions from full-disk magnetograms that lack the necessary resolution to reveal their true magnetic origin.

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