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Title: X-ray line coincidence photopumping in a solar flare

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.
Authors:
 [1] ; ORCiD logo [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Queen’s Univ., Belfast (United Kingdom). Astrophysics Research Centre, School of Mathematics and Physics
  2. Imperial College, London (United Kingdom). Blackett Lab.
  3. California State Univ. (CalState), Northridge, CA (United States). Dept. of Physics and Astronomy
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Univ. of Notre Dame, IN (United States). Dept. of Physics
Publication Date:
Report Number(s):
LLNL-JRNL-739147
Journal ID: ISSN 0035-8711
Grant/Contract Number:
AC52-07NA27344; 606862
Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 474; Journal Issue: 3; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE; European Union (EU)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 79 ASTRONOMY AND ASTROPHYSICS; line: identification; radiative transfer; Sun: corona; Sun: flares; stars: coronae; stars: flare
OSTI Identifier:
1438781

Keenan, F. P., Poppenhaeger, K., Mathioudakis, M., Rose, S. J., Flowerdew, J., Hynes, D., Christian, D. J., Nilsen, J., and Johnson, W. R.. X-ray line coincidence photopumping in a solar flare. United States: N. p., Web. doi:10.1093/mnras/stx3035.
Keenan, F. P., Poppenhaeger, K., Mathioudakis, M., Rose, S. J., Flowerdew, J., Hynes, D., Christian, D. J., Nilsen, J., & Johnson, W. R.. X-ray line coincidence photopumping in a solar flare. United States. doi:10.1093/mnras/stx3035.
Keenan, F. P., Poppenhaeger, K., Mathioudakis, M., Rose, S. J., Flowerdew, J., Hynes, D., Christian, D. J., Nilsen, J., and Johnson, W. R.. 2017. "X-ray line coincidence photopumping in a solar flare". United States. doi:10.1093/mnras/stx3035. https://www.osti.gov/servlets/purl/1438781.
@article{osti_1438781,
title = {X-ray line coincidence photopumping in a solar flare},
author = {Keenan, F. P. and Poppenhaeger, K. and Mathioudakis, M. and Rose, S. J. and Flowerdew, J. and Hynes, D. and Christian, D. J. and Nilsen, J. and Johnson, W. R.},
abstractNote = {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.},
doi = {10.1093/mnras/stx3035},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 3,
volume = 474,
place = {United States},
year = {2017},
month = {11}
}