X-Ray Spectroscopy in the Microcalorimeter Era 4: Optical Depth Effects on the Soft X-Rays Studied with Cloudy

In this paper, we discuss atomic processes modifying the soft X-ray spectra from optical depth effects like photoelectric absorption and electron scattering suppressing the soft X-ray lines. We also show the enhancement in soft X-ray line intensities in a photoionized environment via continuum pumping. We quantify the suppression/enhancement by introducing a line modification factor (f (mod)). If 0 <= f (mod) <= 1, the line is suppressed, which could be the case in both collisionally ionized and photoionized systems. If f (mod) >= 1, the line is enhanced, which occurs in photoionized systems. Hybrid astrophysical sources are also very common, where the environment is partly photoionized and partly collisionally ionized. Such a system is V1223 Sgr, an Intermediate Polar binary. We show the application of our theory by fitting the first-order Chandra Medium Energy Grating (MEG) spectrum of V1223 Sgr with a combination of Cloudy-simulated additive cooling-flow and photoionized models. In particular, we account for the excess flux for O vii, O viii, Ne ix, Ne x, and Mg xi lines in the spectrum found in a recent study, which could not be explained with an absorbed cooling-flow model.

Automated summary

This paper discusses the impact of optical depth effects such as photoelectric absorption and electron scattering on soft X-ray spectra, as well as the enhancement of soft X-ray line intensities in a photoionized environment through continuum pumping. The suppression/enhancement is quantified using a line modification factor. The study also applies the theory to fitting the spectrum of V1223 Sgr and explains the excess flux for certain lines that couldn't be explained by an absorbed cooling-flow model.