Abstract
For more than 40 years, most astrophysical observations and laboratory studies of two key soft x-ray diagnostic 2p-3d transitions, 3C and 3D, in Fe XVII ions found oscillator strength ratios f(3C)/f(3D) disagreeing with theory, but uncertainties had precluded definitive statements on this much studied conundrum. Here, we resonantly excite these lines using synchrotron radiation at PETRA III, and reach, at a millionfold lower photon intensities, a 10 times higher spectral resolution, and 3 times smaller uncertainty than earlier work. Our final result of f(3C)/f(3D)=3.09(8)(6) supports many of the earlier clean astrophysical and laboratory observations, while departing by five sigmas from our own newest large-scale ab initio calculations, and excluding all proposed explanations, including those invoking nonlinear effects and population transfers.
| Original language | English |
|---|---|
| Article number | 225001 |
| Journal | Physical Review Letters |
| Volume | 124 |
| Issue number | 22 |
| DOIs | |
| State | Published - Jun 5 2020 |
Funding
Financial support was provided by the Max-Planck-Gesellschaft and Bundesministerium f\u00FCr Bildung und Forschung through Project No. 05K13SJ2. Work by C.\u2009S. was supported by the Deutsche Forschungsgemeinschaft Project No. 266229290 and by an appointment to the NASA Postdoctoral Program at the NASA Goddard Space Flight Center, administered by Universities Space Research Association under contract with NASA. Work by LLNL was performed under the auspices of the U.S. Department of Energy under Contract No. DE-AC52-07NA27344 and supported by NASA grants. M.\u2009A.\u2009L. and F.\u2009S.\u2009P. acknowledge support from NASA\u2019s Astrophysics Program. The work of M.\u2009G.\u2009K. and S.\u2009G.\u2009P. was supported by the Russian Science Foundation under Grant No. 19-12-00157. The theoretical research was supported in part through the use of Information Technologies resources at the University of Delaware, specifically the high-performance Caviness computing cluster. The work of C.\u2009C. and M.\u2009S.\u2009S. was supported by USA NSF Grant No. PHY-1620687. Work by U.\u2009N.\u2009I.\u2009S.\u2009T. was supported by the National Research Foundation of Korea (Grant No. NRF-2016R1A5A1013277). J.\u2009C.\u2009B. acknowledges support from the Alexander von Humboldt Foundation. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III.