Narrow-line-width UV bursts in the transition region above Sunspots observed by IRIS

Abstract

Various small-scale structures abound in the solar atmosphere above active regions, playing an important role in the dynamics and evolution therein. We report on a new class of small-scale transition region structures in active regions, characterized by strong emissions but extremely narrow Si IV line profiles as found in observations taken with the Interface Region Imaging Spectrograph (IRIS). Tentatively named as Narrow-line-width UV bursts (NUBs), these structures are located above sunspots and comprise of one or multiple compact bright cores at sub-arcsecond scales. We found six NUBs in two datasets (a raster and a sit-and-stare dataset). Among these, four events are short-living with a duration of $\sim$10 mins while two last for more than 36 mins. All NUBs have Doppler shifts of 15--18 km/s, while the NUB found in sit-and-stare data possesses an additional component at $\sim$50 km/s found only in the C II and Mg II lines. Given that these events are found to play a role in the local dynamics, it is important to further investigate the physical mechanisms that generate these phenomena and their role in the mass transport in sunspots.

arXiv comment8 pages, 4 figures and 1 table, accepted for publication in ApJL

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Cited by in corpus (9)

• Solar ultraviolet bursts
• A Magnetic Reconnection model for Hot Explosions in the Cool Atmosphere of the Sun
• Coronal Condensation as the Source of Transition Region Supersonic Downflows above a Sunspot
• Solar Ultraviolet Bursts in a Coordinated Observation of IRIS, Hinode and SDO
• Coronal heating and solar wind formation in quiet Sun and coronal holes: a unified scenario
• Observations of upward propagating waves in the transition region and corona above Sunspots
• Non-equilibrium ionization by a periodic electron beam II. Synthetic Si IV and O IV transition region spectra
• The Ellerman bomb and Ultraviolet burst triggered successively by an emerging magnetic flux rope
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)