Carbon X-ray absorption in the local ISM: fingerprints in X-ray Novae spectra

TL;DR

This study analyzes carbon absorption lines in X-ray spectra of novae to understand interstellar medium properties, using high-resolution data to benchmark atomic models and determine ISM temperature conditions.

Contribution

It provides improved atomic data for C K-edge absorption lines and confirms their interstellar origin through spectral analysis of novae during the SSS phase.

Findings

Absorption lines due to C II and C III identified in nova spectra.

Atomic data benchmarking shows wavelength shifts and cross-section adjustments.

Maximum ISM temperature estimated at below 3.05×10^4 K.

Abstract

We present a study of the C K-edge using high-resolution LETGS Chandra spectra of four novae during their super-soft-source (SSS) phase. We identified absorption lines due to C~ii K$\alpha$, C~iii K$\alpha$ and C~ iii K$\beta$ resonances. We used these astronomical observations to perform a benchmarking of the atomic data, which involves wavelength shifts of the resonances and photoionization cross-sections. We used improved atomic data to estimate the C~ii and C~iii column densities. The absence of physical shifts for the absorption lines, the consistence of the column densities between multiple observations and the high temperature required for the SSS nova atmosphere modeling support our conclusion about an ISM origin of the respective absorption lines. Assuming a collisional ionization equilibrium plasma the maximum temperature derived from the ratio of C~ii/C~iii column densities of the absorbers correspond to $T_{max}< 3.05\times10^{4}$ K.