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X-ray line coincidence photopumping in a solar flare

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Title: X-ray line coincidence photopumping in a solar flare
Authors: Rose, SJ
Keenan, FP
Poppenhaeger, K
Mathioudakis, M
Flowerdew, J
Hynes, D
Christian, DJ
Nilsen, J
Johnson, WR
Item Type: Journal Article
Abstract: Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of line coincidence photopumping in astrophysical sources at optical and ultraviolet wavelengths, with the most famous example being Bowen fluorescence (pumping of O III 303.80 Å by He II), but none to our knowledge in X-rays. However, here we report on a scheme where a He-like line of Ne IX at 11.000 Å is photopumped by He-like Na X at 11.003 Å, which predicts significant intensity enhancement in the Ne IX 82.76 Å transition under physical conditions found in solar flare plasmas. A comparison of our theoretical models with published X-ray observations of a solar flare obtained during a rocket flight provides evidence for line enhancement, with the measured degree of enhancement being consistent with that expected from theory, a truly surprising result. Observations of this enhancement during flares on stars other than the Sun would provide a powerful new diagnostic tool for determining the sizes of flare loops in these distant, spatially unresolved, astronomical sources.
Issue Date: 23-Nov-2017
Date of Acceptance: 16-Nov-2017
URI: http://hdl.handle.net/10044/1/56091
DOI: https://dx.doi.org/10.1093/mnras/stx3035
ISSN: 0035-8711
Publisher: Oxford University Press (OUP)
Start Page: 3782
End Page: 3786
Journal / Book Title: Monthly Notices of the Royal Astronomical Society
Volume: 474
Issue: 3
Copyright Statement: Copyright © 2017, Oxford University Press
Keywords: 0201 Astronomical And Space Sciences
Astronomy & Astrophysics
Publication Status: Published
Appears in Collections:Physics
Plasma Physics
Faculty of Natural Sciences