Termination shocks and the extended X-ray emission in Mrk 78

Abstract

Subarcsecond imaging of the X-ray emission in the type 2 active galactic nucleus (AGN) Mrk 78 with Chandra shows complex structure with spectral variations on scales from ∼200 pc to ∼2 kpc. Overall the X-ray emission is aligned E–W with the radio (3.6 cm) and narrow emission line region as mapped in [O III], with a marked E–W asymmetry. The eastern X-ray emission is mostly in a compact knot coincident with the location where the radio source is deflected, while the western X-ray emission forms a loop or shell ∼2 kpc from the nucleus with radius ∼0.7 kpc. There is suggestive evidence of shocks in both the eastern knot and the western arc. Both these positions coincide with large changes in the velocities of the [O III] outflow. We discuss possible reasons why the X-ray shocks on the western side occur ∼1 kpc farther out than on the eastern side. We estimate that the thermal energy injected by the shocks into the interstellar medium corresponds to 0.05%–0.6% of the AGN bolometric luminosity.