The Powerful Outburst in Hercules A

Authors

P. Nulsen, University of Wollongong
D. C. Hambrick, Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
B. R. McNamara, Ohio University, USA
D. Rafferty, Ohio University, USA
L. Birzan, Ohio University, USA
M. W. Wise, Massachusetts Institute of Technology, USA
L. P. David, Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

RIS ID

73553

Publication Details

This article was originally published as: Nulsen, PEJ, Hambrick, DC, McNamara, BR, et al, The Powerful Outburst in Hercules A, The Astrophysical Journal, 2005, 625(1), L9-L12. Copyright 2005 University of Chicago Press. The journal can be found here.

Abstract

The radio source Hercules A resides at the center of a cooling flow cluster of galaxies at redshift z = 0.154. A Chandra X-ray image reveals a shock front in the intracluster medium (ICM) surrounding the radio source, about 160 kpc from the active galactic nucleus (AGN) that hosts it. The shock has a Mach number of 1.65, making it the strongest of the cluster-scale shocks driven by an AGN outburst found so far. The age of the outburst is 5.9 × 10⁷ yr, its energy ~3 × 10⁶¹ ergs, and its mean power ~1.6 × 10⁴⁶ ergs s^-1. As for the other large AGN outbursts in cooling flow clusters, this outburst overwhelms radiative losses from the ICM of the Hercules A Cluster by a factor of ~100. It adds to the case that AGN outbursts are a significant source of preheating for the ICM. Unless the mechanical efficiency of the AGN in Hercules A exceeds 10%, the central black hole must have grown by more than 1.7 × 10⁸ M_☉ to power this one outburst.