2019ApJ...871..207U

We present line-of-sight (LOS) gas sloshing first found in a cool core in a galaxy cluster. The galaxy cluster Abell 907 is identified as a relaxed cluster owing to its global X-ray surface brightness taken by the Chandra X-ray Observatory. The X-ray residual image after removing the global emission of the intracluster medium (ICM), however, shows an arc-like positive excess and a negative excess surrounding the central positive excess in the cluster core, which in turn indicates a disturbance of the ICM. We analyze the X-ray spectra extracted from both regions and find that (1) the ICM temperature and the metal abundance in the positive excess are lower and higher than those in the negative excess, respectively, and (2) the ICM is nearly in pressure equilibrium. We also find a slight redshift difference between the positive and the negative excesses, which corresponds to the velocity shear of 1680_–920⁺¹³⁰⁰ km s^–1 (1σ). The X-ray residual image and the ICM properties are consistent with those expected by LOS gas sloshing. Assuming that the gas is moving inverse-parallel to each other along the LOS, the shear velocity is expected to be ∼800 km s^–1. The velocity field of this level is able to provide nonthermal pressure support by ∼34% relative to the thermal one. The total kinetic energy inferred from the shear velocity corresponds to ∼30% of the bolometric luminosity of the sloshing ICM. Abell 907 is therefore complementary to galaxy clusters in which gas sloshing takes place in the plane of the sky, and is important for understanding gas dynamics driven by sloshing and its influence on the heating to prevent runaway cooling.