Suzaku and Chandra Observations of CIZA J1700.8$-$3144, a Cluster of Galaxies in the Zone of Avoidance

Abstract

We present the Chandra and Suzaku observations of 1RXS J170047.8$-$314442, located towards the Galactic bulge, to reveal a wide-band ($0.3$-$10$ keV) X-ray morphology and spectrum of this source. With the Chandra observation, no point source was found at the position of 1RXS J170047.8$-$314442. Alternatively, we revealed the presence of diffuse X-ray emission by the wide-band X-ray image obtained from the Suzaku XIS. Although the X-ray emission had a nearly circular shape with a spatial extent of $\sim 3.5'$, the surface brightness profile was not axisymmetric; a bright spot-like emission was found at $\sim 1'$ away in the north-western direction from the center. The radial profile of the surface brightness, except for this spot-like emission, was reproduced with a single $\beta$-model; $\beta$ and the core radius were found to be $1.02$ and $1.51'$, respectively. The X-ray spectrum of the diffuse emission showed an emission line at $\sim 6$ keV, indicating an origin of a thermal plasma. The spectrum was well explained with an absorbed optically-thin thermal plasma model with a temperature of $6.2$ keV and a redshift parameter of $z = 0.14 \pm 0.01$. Hence, the X-ray emission was considered to arise from the hot gas associated with a cluster of galaxies. Our spectroscopic result confirmed the optical identification of 1RXS J170047.8$-$314442 by Kocevski et al. (2007): CIZA J1700.8$-$3144, a member of the cluster catalogue in the Zone of Avoidance. The estimated bolometric X-ray luminosity of $5.9 \times 10^{44}$ erg s$^{-1}$ was among the lowest with this temperature, suggesting that this cluster is far from relaxed.