Characterization of diffuse X-ray emission from IGR J17448–3232: an implication of a line-of-sight merging activity

The results of spectral analysis for the galaxy cluster IGR J17448$-$3232 are presented. The intracluster medium (ICM) in the central region ($r\lt 300^{\prime \prime }$, $320\:$kpc) has a high electron temperature plasma of $kT_{\rm e} \sim 13$–$15\:$keV, and an ionization temperature estimated from an intensity ratio of Fe xxvi Ly$\alpha /$Fe xxv He$\alpha$ lines is lower than the electron temperature, which suggests that the ICM is in the non-ionization equilibrium (NEI) state. The spectrum in the central region can be also fitted with a two-component model: a two-temperature plasma model in a collisional ionization equilibrium (CIE) with temperatures of $7.9\:$keV and $\gt 34\:$keV, or a CIE$+$power-law model with a temperature of $9.4\:$keV and a photon index of 1.1. The two-component models can represent the intensity ratio of Fe xxvi Ly$\alpha /$Fe xxv He$\alpha$ lines. On the other hand, the spectrum in the outer region ($r\gt 300^{\prime \prime }$) can be explained by a single CIE plasma model with a temperature of 5–$8\:$keV. Based on the spectral feature and its circular structure, we propose that the NEI plasma was produced by merging along the line-of-sight direction.