Photoexcitation spectroscopy of highly charged ions for application to astronomy using a compact electron beam ion trap (EBIT) at the synchrotron radiation facility SPring-8

TL;DR

This study develops a specialized electron beam ion trap (EBIT) at SPring-8 to obtain high-resolution atomic spectra of highly charged ions, improving atomic data accuracy for astrophysical X-ray spectral analysis.

Contribution

The paper introduces a new EBIT design compatible with synchrotron radiation facilities, enabling precise experimental measurements of atomic spectra of highly charged ions relevant to astronomy.

Findings

Successfully measured high-resolution spectra of Ne-like Fe$^{16+}$ and He-like O$^{6+}$ ions.

Constrained the oscillator strength ratio of specific Fe$^{16+}$ resonance transitions.

Provided experimental atomic data to enhance astrophysical plasma spectral models.

Abstract

In the past few decades, X-ray astronomy satellites equipped with grating spectrometers and microcalorimeters have enabled high-resolution spectroscopic observations of astrophysical objects. The need for accurate atomic data has arose as we attempt detailed analysis of the high-resolution spectra they provide. This is because current spectral models, which heavily rely on theoretical calculations, entail non-negligible uncertainties. We employ a plasma spectroscopy device called electron beam ion trap (EBIT) to experimentally obtain precise atomic data. An EBIT with a design that allows combined operation with synchrotron radiation facilities was developed based on the Heidelberg Compact EBIT and installed at ISAS/JAXA for this purpose. We conducted a spectroscopic experiment using the JAXA-EBIT at the synchrotron radiation facility SPring-8, and successfully obtained high-resolution spectra of the L$\alpha$ resonance transition of Ne-like Fe$^{16+}$ ions, 3C, as well as the K$\alpha$ resonance transition of He-like O$^{6+}$ ions. We also measured another Ne-like Fe$^{16+}$ L$\alpha$ resonance transition, 3G, and constrained an upper limit of the oscillator strength ratio of 3G to 3C, using our experimental results. The experimental values obtained in this study will be applied to observational studies of astrophysical objects as a part of the plasma spectral modeling.