IRIS observations of magnetic interactions in the solar atmosphere between pre-existing and emerging magnetic fields. II. UV emission properties

Abstract

Multi-wavelength ultraviolet (UV) observations by the IRIS satellite in active region NOAA 12529 have recently pointed out the presence of long-lasting brightenings, akin to UV bursts, and simultaneous plasma ejections occurring in the upper chromosphere and transition region during secondary flux emergence. These signatures have been interpreted as evidence of small-scale, recurrent magnetic reconnection episodes between the emerging flux region (EFR) and the pre-existing plage field. Here, we characterize the UV emission of these strong, intermittent brightenings and we study the surge activity above the chromospheric arch filament system (AFS) overlying the EFR. We analyze the surges and the cospatial brightenings observed at different wavelengths. We find an asymmetry in the emission between the blue and red wings of the Si IV 1402 Å and Mg II k 2796.3 Å lines, which clearly outlines the dynamics of the structures above the AFS that form during the small-scale eruptive phenomena. We also detect a correlation between the Doppler velocity and skewness of the Si IV 1394 Å and 1402 Å line profiles in the UV burst pixels. Finally, we show that genuine emission in the Fe XII 1349.4 Å line is cospatial to the Si IV brightenings. This definitely reveals a pure coronal counterpart to the reconnection event.

19 pages, 8 figures + 3 figures in the Appendix; accepted in ApJ

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• Ellerman bombs and UV bursts: reconnection at different atmospheric layers
• Extreme-ultraviolet bursts and nanoflares in the quiet-Sun transition region and corona
• An observationally-constrained model of strong magnetic reconnection in the solar chromosphere. Atmospheric stratification and estimates of heating rates
• A Magnetic Reconnection model for Hot Explosions in the Cool Atmosphere of the Sun
• A 2D Model for Coronal Bright Points: Association with Spicules, UV bursts, Surges and EUV Coronal Jets
• Solar surges related to UV bursts: Characterization through k-means, inversions and density diagnostics
• Emergence of small-scale magnetic flux in the quiet Sun
• Small-scale magnetic flux emergence preceding a chain of energetic solar atmospheric events
• Transition region loops in the very late phase of flux-emergence in IRIS sit-and-stare observations
• The Ellerman bomb and Ultraviolet burst triggered successively by an emerging magnetic flux rope
• The Transition Region of Solar Flare Loops
• Penumbral brightening events observed in AR NOAA 12546
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Signatures of Untwisting Magnetic Field in a Small Emerging Bipole in the Solar Photosphere
• Hard X-rays from the deep solar atmosphere. An unusual UV burst with flare properties
• Emergence of internetwork magnetic fields through the solar atmosphere
• Observations of the formation of a proto-spot in a pre-existing field environment