We have used a 50.4 ksec Chandra observation to examine the galaxy cluster Abell 115 ( z =0.1971 ) .
The X-ray surface brightness distribution shows a merger of 2 sub-clusters with substantial off-axis motion .
The northern sub-cluster moves toward the southwest and exhibits a strong X-ray surface brightness gradient toward this direction as well as a “ fan ” of X-ray bright Intra-Cluster Medium ( ICM ) toward the northeast .
The southern sub-cluster shows a pronounced northeast-southwest elongation , probably as a consequence of the ongoing merger .
The temperature of the ICM is highly non-uniform across the cluster .
Although the merger is well underway and has had a substantial influence on the morphology of the 2 sub-clusters , it has apparently not disturbed the cool sub-cluster cores : the cores show projected temperatures of \sim 3 keV and are substantially cooler than the surrounding plasma of \sim 5 keV .
The ICM in between the sub-clusters has a significantly elevated temperature of \sim 8 keV .
However , owing to the low surface brightness , we do not find direct evidence for shocks in this region .
The X-ray surface brightness distribution of the northern sub-cluster is highly non-uniform .
The data show a bright central core region of about 10 ” ( 30 kpc ) diameter .
A highly significant surface brightness discontinuity separates the core from the ambient ICM .
We discuss several possibilities to explain the compact core , and its relation to the central radio galaxy 3C 28.0 and the sub-cluster ’ s cooling flow .
Further outwards , at about 24.6 ” ( 80 kpc ) to the southwest of the sub-cluster core , the surface brightness distribution shows a jump associated with a contact discontinuity .
The Chandra imaging spectroscopy data do not show evidence for a shock associated with the surface brightness jump .
We conclude that it is associated with denser plasma moving sub-sonically through the ambient plasma .