New Insights with XRISM & Cloudy: A novel Column Density Diagnostic

TL;DR

This paper introduces a new X-ray plasma diagnostic using the Lyα line ratio, enabled by recent spectral simulation advances and high-resolution observations, applicable to various ionized astrophysical plasmas.

Contribution

It presents a novel column density diagnostic based on Lyα line ratios, leveraging Cloudy simulations and XRISM data, for the first time.

Findings

The Lyα line ratio can be used to determine plasma column density.

The diagnostic is demonstrated with XRISM observations of Centaurus X-3.

Applicable to both collisionally and radiatively ionized plasmas.

Abstract

We present a simple, yet powerful column density diagnostic for plasmas enabled by X-ray microcalorimeter observations. With the recent developments of the spectral simulation code Cloudy, inspired by the high spectral resolution of the X-Ray Imaging and Spectroscopy Mission (XRISM) and the Advanced Telescope for High Energy Astrophysics (Athena), we make predictions for the intensity ratio of the resolved fine-structure lines Ly$\alpha_1$ and Ly$\alpha_2$ of H-like ions. We show that this ratio can be observationally constrained and used as a plasma column density indicator. We demonstrate this with a XRISM observation of the high-mass X-ray binary Centaurus X-3. This diagnostic is useful for a wide range of X-ray emitting plasmas, either collisionally or radiatively ionized.