Kühn Steffen, Cheung Charles, Oreshkina Natalia S, Steinbrügge René, Togawa Moto, Bernitt Sonja, Berger Lukas, Buck Jens, Hoesch Moritz, Seltmann Jörn, Trinter Florian, Keitel Christoph H, Kozlov Mikhail G, Porsev Sergey G, Gu Ming Feng, Porter F Scott, Pfeifer Thomas, Leutenegger Maurice A, Harman Zoltán, Safronova Marianna S, López-Urrutia José R Crespo, Shah Chintan
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
Heidelberg Graduate School of Fundamental Physics, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 226, 69120 Heidelberg, Germany.
Phys Rev Lett. 2022 Dec 9;129(24):245001. doi: 10.1103/PhysRevLett.129.245001.
One of the most enduring and intensively studied problems of x-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of crucial value for plasma diagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power 2.5 times and the signal-to-noise ratio thousandfold compared with our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio R_{exp}=f_{3C}/f_{3D}=3.51(2){stat}(7){sys} agrees with our state-of-the-art calculation of R_{th}=3.55(2), as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of 3C and 3D transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.
