Conclusions

Chandra imaging spectroscopy of the intermediate FRI/FRII radio-galaxy 3C 401 reveals clear signs of an interaction between the radio-galaxy and the ICM of its surrounding cluster. Although we do not see well defined ICM cavities (most likely due to the limited number of photons in our image), the flattening of the central X-ray isophotes strongly suggests that the radio-lobes are indeed evacuating cavities within the ICM with a radius of 15-20kpc. There are also deviations from spherical symmetry on much larger spatial scales (100kpc or more) that reveal themselves as a cross-like structure in the low surface brightness regions of the ICM. It is tantalizing to speculate that a previous, much more powerful period of activity from 3C 401 created these large scale disturbances. While this large scale cross-like pattern might be caused by a pair of ghost cavities related to previous activity, the symmetry of this structure leads us to speculate that the ICM atmosphere is executing large-amplitude, low-$l$ g-mode oscillations. Deeper imaging of this field (either with a very long Chandra observation or a moderately deep XMM-Newton observation) is required to further probe these possibilities.

The ICM possesses a temperature of $kT\approx 2.9{\rm\thinspace keV}$ and a 0.5-10keV luminosity of $L_{0.5-10}=5.6\times 10^{43}\hbox{${\rm\thinspace erg}{\rm\thinspace s}^{-1}\,$}$ placing it firmly on the standard L-T relationship of Horner (2002). This cluster also possesses an X-ray luminosity typical for its cluster richness (B$_{gg}$ value; Yee & Ellingson 2003), although its T$_x$ is nearly a factor of two below that expected for its richness (Yee & Ellingson 2003). In addition, its surface brightness profile is unusually flat. When parameterized by a standard King-type model, the ICM possesses $\beta=0.46$, much flatter than the normal $\beta=0.67$ found in clusters of comparable or greater mass. These unusual ICM features may all be due to the unusually large radio power level of the central galaxy for a cluster with a dense ICM. However, because this analysis uses only a few thousand X-ray photons total, we worry that the ICM surface brightness distribution may not have been measured robustly as yet.

This system is ripe for deeper X-ray imaging spectroscopy, either with a long Chandra stare or a moderately long XMM-Newton observation. With such data, we will be able to search for the well-defined ICM cavities that probably encase the currently active radio-lobes, study the cross-like structure on 170kpc scales, and constrain the ICM surface brightness profile significantly beyond 100kpc. New data of this type will take studies of the current radio-galaxy/ICM interaction as well as the ICM thermodynamics of the 3C 401 system to the next level.