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Automating Ellerman bomb detection in ultraviolet continua
Stockholm University, Faculty of Science, Department of Astronomy. University of Oslo, Norway.
Number of Authors: 32019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 626, article id A4Article in journal (Refereed) Published
Abstract [en]

Ellerman bombs are transient brightenings in the wings of H alpha 6563 angstrom that pinpoint photospheric sites of magnetic reconnection in solar active regions. Their partial visibility in the 1600 angstrom and 1700 angstrom continua registered routinely by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) offers a unique opportunity to inventory such magnetic-field disruptions throughout the AIA database if a reliable recipe for their detection can be formulated. This is done here. We have improved and applied an H alpha Ellerman bomb detection code to ten data sets spanning viewing angles from solar disc centre to the limb. They combine high-quality H alpha imaging spectroscopy from the Swedish 1 m Solar Telescope with simultaneous AIA imaging around 1600 angstrom and 1700 angstrom. A trial grid of brightness, lifetime and area constraints is imposed on the AIA images to define optimal recovery of the 1735 Ellerman bombs detected in H alpha. The best results when optimising simultaneously for recovery fraction and reliability are obtained from 1700 angstrom images by requiring 5 sigma - brightening above the average 1700 angstrom nearby quiet-Sun intensity, lifetime above one minute, area of 1-18 AIA pixels. With this recipe 27% of the AIA detections are Ha-detected Ellerman bombs while it recovers 19% of these (of which many are smaller than the AIA resolution). Better yet, among the top 10% AIA 1700 angstrom detections selected with combined brightness, lifetime and area thresholds as many as 80% are H alpha Ellerman bombs. Automated selection of the best 1700 angstrom candidates therefore opens the entire AIA database for detecting most of the more significant photospheric reconnection events. This proxy is applicable as a flux-dynamics tell-tale in studying any Earth-side solar active region since early 2010 up to the present.

Place, publisher, year, edition, pages
2019. Vol. 626, article id A4
Keywords [en]
Sun: activity, Sun: atmosphere, Sun: magnetic fields, Sun: UV radiation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-170007DOI: 10.1051/0004-6361/201834811ISI: 000469410500003OAI: oai:DiVA.org:su-170007DiVA, id: diva2:1330862
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved

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