Discovery of ghost cavities in the X-ray atmosphere of Abell 2597

A Chandra image of the central 100 kpc of the Abell 2597 cluster of galaxie s shows bright irregular X-ray emission within the central dominant cluster galaxy (CDG) and two low surface brightness cavities located 30 kpc from t he nucleus of the CDG. Unlike the cavities commonly seen in other clusters, the "ghost" cavities in Abell 2597 are not coincident with the bright cent ral radio source. Instead, they appear to be associated with faint extended radio emission seen in a deep Very Large Array radio map. We interpret the ghost cavities as buoyantly rising relics of a radio outburst that occurre d between 50 and 100 Myr ago. The demography of cavities in the few cluster s studied thus far shows that galactic radio sources experience recurrent o utbursts on an similar to 100 Myr timescale. Over the lifetime of a cluster , ghost cavities emerging from CDGs deposit greater than or similar to 10(5 9)-10(61) ergs of energy into the intracluster medium. If a significant fra ction of this energy is deposited as magnetic field, it would account for t he high field strengths in the cooling flow regions of clusters. The simila rity between the central cooling time of the keV gas and the radio cycling timescale suggests that feedback between cooling gas and the radio source m ay be retarding or quenching the cooling flow.