Structual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines

TL;DR

This study analyzes the structure of hot gas in the Milky Way's halo toward Mkn 421 using X-ray absorption and emission lines, revealing a thick disk-like hot gas distribution with specific temperature, density, and scale height parameters.

Contribution

It provides the first joint analysis of absorption and emission lines to constrain the temperature, density, and scale height of hot gas in the Galactic halo along this sight line.

Findings

Hot gas temperature at the Galactic plane is approximately 3.2 million K.

Density of the hot gas at the plane is about 1.2 x 10^-3 cm^-3.

Scale height of the hot gas is around 1.6 kpc, indicating a thick disk structure.

Abstract

We present a structural study of the hot ISM in the Galactic halo along the sight line toward the bright active galactic nucleus Mkn 421. The OVII and OVIII absorption lines were measured with the Low Energy Transmission Grating Spectrograph aboard Chandra toward Mkn 421, and the OVII and OVIII emission lines were observed in the adjacent fields of the sight line with the X-ray Imaging Spectrometer aboard Suzaku. We jointly analyzed the absorption and the emission spectra assuming exponential distributions of the gas temperature and density from the Galactic plane, and constrained the temperature and density at the plane to be $(3.2^{+0.6}_{-0.7})\times 10^6\,\mathrm{K}$ and $(1.2^{+0.5}_{-0.4})\times 10^{-3}\,\mathrm{cm^{-3}}$, with the scale heights of $1.6^{+1.7}_{-0.7}\,\mathrm{kpc}$ and $>2.8\,\mathrm{kpc}$ respectively. The results are consistent with those obtained in the LMC X-3 direction and the PKS 2155-304 direction, describing a thick disk-like hot gas with its height of a few kpc from the Galactic plane.