The Cluster‐Scale AGN Outburst in Hydra A

Deep Chandra observations of the Hydra A Cluster reveal a feature in theX-ray surface brightness that surrounds the 330 MHz radio lobes of the AGN atthe cluster center. Surface brightness profiles of this feature and its closeassociation with the radio lobes argue strongly that it is a shock front drivenby the expanding radio lobes. The Chandra image also reveals other newstructure on smaller scales that is associated with the radio source, includinga large cavity and filament. The shock front extends 200 - 300 kpc from the AGNat the cluster center and its strength varies along the front, with Machnumbers in the range ~ 1.2 - 1.4. It is stronger where it is more distant fromthe cluster center, as expected for a shock driven by expanding radio lobes.Simple modeling gives an age for the shock front ~ 1.4\times10^8 y and a totalenergy driving it of ~ 10^{61} erg. The mean mechanical power driving the shockis comparable to quasar luminosities, well in excess of that needed to regulatethe cooling core in Hydra A. This suggests that the feedback regulating coolingcores is inefficient, in that the bulk of the energy is deposited beyond thecooling core. In that case, a significant part of cluster "preheating" is abyproduct of the regulation of cooling cores.Comment: 7 pages, 6 figures, submitted to Ap