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

Abstract

The results of spectral analysis for the galaxy cluster IGR J17448-3232 are presented. The intracluster medium (ICM) in the central region (r< 300^' ' }, 320kpc) has a high electron temperature plasma of kT_e ∼ 13-15keV, and an ionization temperature estimated from an intensity ratio of Fe XXVI Lyα /Fe XXV Heα 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 7.9keV and > 34keV, or a CIE+power-law model with a temperature of 9.4keV and a photon index of 1.1. The two-component models can represent the intensity ratio of Fe XXVI Lyα /Fe XXV Heα lines. On the other hand, the spectrum in the outer region (r> 300^' ' }) can be explained by a single CIE plasma model with a temperature of 5-8keV. 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.