Probing X-ray Absorption and Optical Extinction in the Interstellar Medium Using Chandra Observations of Supernova Remnants

TL;DR

This study uses Chandra observations of supernova remnants to analyze interstellar X-ray absorption and optical extinction, refining the empirical relation between hydrogen column density and optical extinction with a comprehensive Bayesian approach.

Contribution

It provides a new, more accurate empirical relation between hydrogen column density and optical extinction by addressing systematic uncertainties in X-ray absorption measurements.

Findings

Refined the NH-AV relation to (2.87±0.12) x 10^21 cm^(-2)

Quantified systematic uncertainties using Bayesian methods

Found the new relation is significantly higher than previous estimates

Abstract

We present a comprehensive study of interstellar X-ray extinction using the extensive Chandra supernova remnant archive and use our results to refine the empirical relation between the hydrogen column density and optical extinction. In our analysis, we make use of the large, uniform data sample to assess various systematic uncertainties in the measurement of the interstellar X-ray absorption. Specifically, we address systematic uncertainties that originate from (i) the emission models used to fit supernova remnant spectra, (ii) the spatial variations within individual remnants, (iii) the physical conditions of the remnant such as composition, temperature, and non-equilibrium regions, and (iv) the model used for the absorption of X-rays in the interstellar medium. Using a Bayesian framework to quantify these systematic uncertainties, and combining the resulting hydrogen column density measurements with the measurements of optical extinction toward the same remnants, we find the empirical relation NH = (2.87+/-0.12) x 10^21 AV cm^(-2), which is significantly higher than the previous measurements.