Multiwavelength Observations of Radio Galaxy 3C 120 with XMM-Newton

January 2005 • 2005ApJ...618..139O

Authors • Ogle, P. M. • Davis, S. W. • Antonucci, R. R. J. • Colbert, J. W. • Malkan, M. A. • Page, M. J. • Sasseen, T. P. • Tornikoski, M.

Abstract • We present XMM-Newton observations of the radio galaxy 3C 120. Contemporaneous radio, millimeter-wave, and optical data provide additional constraints on the spectral energy distribution and physical state of the active galactic nucleus. The hard X-ray spectrum contains a marginally resolved Fe I Kα emission line with FWHM=9000+/-3000 km s^-1 and an equivalent width of 57+/-7 eV. The line arises via fluorescence in a broad-line region with covering fraction of 0.4. There is no evidence of relativistically broad Fe Kα, contrary to some previous reports. An excess of 0.3-2 keV soft X-ray continuum over an extrapolation of the hard X-ray power law may arise in a disk corona. A break in the X-ray spectrum below 0.6 keV indicates an excess neutral hydrogen column density of N_H=(1.0-1.6)×10²¹ cm^-2. However, the neutral absorber must have an oxygen abundance of <1/40 of the solar value to explain the absence of an intrinsic or intervening O I edge. There is no ionized absorption in the soft X-ray spectrum, and we do not detect previously claimed O VIII absorption from the intervening intergalactic medium. Radio observations at 37 GHz show a fast, high-frequency flare beginning near the time of the XMM-Newton observation, which has no obvious effect on the X-ray spectrum. The X-ray spectrum, including the soft excess, became harder as the X-ray flux decreased, with an estimated pivot energy of 40 keV. The UV and soft X-ray fluxes are strongly correlated over the 120 ks duration of the XMM-Newton observation. This is qualitatively consistent with Comptonization of UV photons by a hot corona.

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James Colbert

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