PREPRINT
5370BE6C-B4EF-4323-A921-36B9E70A04CC

# X-ray spectroscopy in the microcalorimeter era 4: Optical depth effects on the soft X-rays studied with CLOUDY

Priyanka Chakraborty, Gary Ferland, Marios Chatzikos, Andrew Fabian, Stefano Bianchi, Francisco Guzmán, Yuanyuan Su
arXiv:2207.02267

Submitted on 5 July 2022

## Abstract

In this paper, we discuss atomic processes modifying the soft X-ray spectra in 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 (${f}_{\mathrm{m}\mathrm{o}\mathrm{d}}$)." If 0 $\le$ ${f}_{\mathrm{m}\mathrm{o}\mathrm{d}}$ $\le$ 1, the line is suppressed, which could be the case in both collisionally-ionized and photoionized systems. If ${f}_{\mathrm{m}\mathrm{o}\mathrm{d}}$ $\ge$ 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 MEG spectrum of V1223 Sgr with a combination of \textsc{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.

## Preprint

Subject: Astrophysics - High Energy Astrophysical Phenomena