High Precision {\it K}-Shell Photoabsorption Cross Sections for Atomic Oxygen: Experiment and Theory

TL;DR

This paper presents high-precision experimental measurements and theoretical calculations of K-shell photoabsorption cross sections for atomic oxygen, crucial for interpreting x-ray astronomical spectra.

Contribution

It provides the first high-resolution experimental data combined with advanced R-matrix theoretical calculations for atomic oxygen's K-shell photoabsorption, improving spectral modeling accuracy.

Findings

Excellent agreement between experiment and theory.

Natural linewidths for Rydberg resonances are accurately determined.

Enhanced understanding of atomic oxygen's role in x-ray spectra.

Abstract

Photoabsorption of atomic oxygen in the energy region below the $\rm 1s^{-1}$ threshold in x-ray spectroscopy from {\it Chandra} and {\it XMM-Newton} is observed in a variety of x-ray binary spectra. Photoabsorption cross sections determined from an R-matrix method with pseudo-states (RMPS) and new, high precision measurements from the Advanced Light Source (ALS) are presented. High-resolution spectroscopy with E/$\Delta$E $\approx$ 4,250 $\pm$ 400 was obtained for photon energies from 520 eV to 555 eV at an energy resolution of 124 $\pm$ 12 meV FWHM. {\it K}-shell photoabsorption cross-section measurements were made with a re-analysis of previous experimental data on atomic oxygen at the ALS. Natural linewidths $\Gamma$ are extracted for the $\rm 1s^{-1}2s^22p^4 (^4P)np ^3P^{\circ}$ and $\rm 1s^{-1}2s^22p^4(^2P)np ~^3P^{\circ}$ Rydberg resonances series and compared with theoretical predictions. Accurate cross sections and linewidths are obtained for applications in x-ray astronomy. Excellent agreement between theory and the ALS measurements is shown which will have profound implications for the modelling of x-ray spectra and spectral diagnostics.