Chandra measurements of 3C 220.1's X-ray core and cluster

Abstract

We report results of an 18 ks exposure with the ACIS instrument on Chandra of the powerful z = 0.62 radio galaxy 3C 220.1. The X-ray emission separates into cluster gas of emission-weighted kT ~ 5 keV and 0.7-12 keV luminosity (to a radius of 45 arcsec) 5.6 x 10^44 ergs s^-1, and unresolved emission (coincident with the radio core). While the extended X-ray emission is clearly thermal in nature, a straightforward cooling-flow model, even in conjunction with a point-source component, is a poor fit to the radial profile of the X-ray emission. This is despite the fact that the measured properties of the gas suggest a massive cooling flow of ~ 130 M_\odot yr^-1, and the data show weak evidence for a temperature gradient. The central unresolved X-ray emission has a power-law spectral energy index \alpha ~ 0.7 and 0.7-12 keV luminosity 10^45 ergs s^-1, and any intrinsic absorption is relatively small. The two-point spectrum of the core emission between radio and X-ray energies has \alpha_rx = 0.75. Since this is a flatter spectrum than seen in other sources where the X-ray emission is presumed to be radio-related, regions close to the AGN in this source may dominate the central X-ray output, as is believed to be the case for lobe-dominated quasars. Simple unification models would be challenged if this were found to be the case for a large fraction of high-power radio galaxies.