Laboratory measurements of Kα transition energies in Ne ions with the XRISM Resolve detector array

With the recent launch of XRISM, the Resolve calorimeter spectrometer makes high-resolution spectroscopy available for a wider range of X-ray sources and makes weaker spectral lines detectable in those sources. Future and proposed observatories like Athena (X-IFU), LEM (calorimeter), and Arcus (gratings) will increase spectral resolution and sensitivity even further. In order to take full advantage of this new discovery space, it is crucial for atomic reference data, which is required for accurate interpretation of observed spectral diagnostics, to be complete and highly accurate. K-shell transitions in L-shell ions have been observed in a variety of elements and sources, but often have no laboratory benchmarks, even for their wavelengths. Accurate line positions are not only relevant for velocity measurements, but also for accurate fits of their line flux. Neutral through Li-like Ne I-VIII have previously been observed in Chandra-HETG observations from ISM absorption along the line of sight to a sample of low-mass X-ray binaries, and, after correcting for the Galactic rotation velocity, measurements of their rest wavelengths have been reported (Liao et al. 2013, ApJ 774, 116). Here, we report laboratory measurements of these Ne line energies. The measurements were taken with XRISM Resolve during the ground calibration campaign for the energy gain scale of the detector assembly with the LLNL WEBIT warm electron beam ion trap. The relatively high background gas load in the warm trap makes WEBIT an ideal source for creating and observing lower charge states of low-Z elements, whose excited states typically have fairly low branching ratios for radiative decay. The transition energies are calibrated in situ against well known lines in He- and H-like O and Ne. This work was supported by LLNL under DOE Contract DE-AC52-07NA27344 and by NASA grants to LLNL and NASA/GSFC.