Abstract
The reported observations of an unidentified X-ray line feature at $\sim$3.5
keV have driven a lively discussion about its possible dark matter origin.
Motivated by this, we have measured the K-shell X-ray spectra of highly
ionized bare sulfur ions following charge exchange with gaseous molecules in an
electron beam ion trap, as a source of or a contributor to this X-ray line. We
produce $S^16+$ and $S^15+$ ions and let them capture
electrons in collision with those molecules with the electron beam turned off
while recording X-ray spectra. We observed a charge-exchanged-induced X-ray
feature at the Lyman series limit (3.47 $\pm$ 0.06 keV). The inferred X-ray
energy is in full agreement with the reported astrophysical observations and
supports the novel scenario proposed by Gu and Kaastra (A & A 584,
L11 (2015)).
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