Ellerman bombs and UV bursts: transient events in chromospheric current sheets

Abstract

Ellerman bombs (EBs) and UV bursts are both brightenings related to flux emergence regions and specifically to magnetic flux of opposite polarity that meet in the photosphere. These two reconnection-related phenomena, nominally formed far apart, occasionally occur in the same location and at the same time, thus challenging our understanding of reconnection and heating of the lower solar atmosphere. We consider the formation of an active region, including long fibrils and hot and dense coronal plasma. The emergence of a untwisted magnetic flux sheet, injected $2.5$~Mm below the photosphere, is studied as it pierces the photosphere and interacts with the preexisting ambient field. Specifically, we aim to study whether EBs and UV bursts are generated as a result of such flux emergence and examine their physical relationship. The Bifrost radiative magnetohydrodynamics code was used to model flux emerging into a model atmosphere that contained a fairly strong ambient field, constraining the emerging field to a limited volume wherein multiple reconnection events occur as the field breaks through the photosphere and expands into the outer atmosphere. Synthetic spectra of the different reconnection events were computed using the $1.5$D RH code and the fully 3D MULTI3D code. The formation of UV bursts and EBs at intensities and with line profiles that are highly reminiscent of observed spectra are understood to be a result of the reconnection of emerging flux with itself in a long-lasting current sheet that extends over several scale heights through the chromosphere. Synthetic diagnostics suggest that there are no compelling reasons to assume that UV bursts occur in the photosphere. Instead, EBs and UV bursts are occasionally formed at opposite ends of a long current sheet that resides in an extended bubble of cool gas.

10 pages, 8 figures, accepted by A&A

References in corpus (9)

• Hot Explosions in the Cool Atmosphere of the Sun
• RH 1.5D: a massively parallel code for multi-level radiative transfer with partial frequency redistribution and Zeeman polarisation
• The effect of the relative orientation between the coronal field and new emerging flux: I Global Properties
• Heating mechanisms in the low solar atmosphere through magnetic reconnection in current sheets
• Magnetic reconnection in strongly magnetized regions of the low solar chromosphere
• Clusters of small eruptive flares produced by magnetic reconnection in the sun
• A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating II. 2D Theory and Simulations
• Estimating the Chromospheric Absorption of Transition Region Moss Emission
• IRIS observations of magnetic interactions in the solar atmosphere between pre-existing and emerging magnetic fields. II. UV emission properties

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