The nature of the multi-wavelength emission of 3C 111

François Arago Centre, APC, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
e-mail: dejong@in2p3.fr

Received: 28 March 2012
Accepted: 12 July 2012

Abstract

Aims. We attempt to determine the nature of the high energy emission of the radio galaxy 3C 111, by distinguishing between the effects of the thermal and non-thermal processes.

Methods. We study the X-ray spectrum of 3C 111 between 0.4 keV and 200 keV, and its spectral energy distribution, using data from the Suzaku satellite combined with INTEGRAL, Swift/BAT data, and Fermi/LAT data. We then model the overall spectral energy distribution by including radio and infrared data.

Results. The combined Suzaku, Swift and INTEGRAL data are represented by an absorbed exponentially cut-off power-law with reflection from neutral material with a photon index Γ = 1.68 ± 0.03, a high-energy cut-off E_cut = 227_-67⁺¹⁴³ keV, a reflection component with R = 0.7 ± 0.3 and a Gaussian component to account for the iron emission-line at 6.4 keV with an equivalent width of EW = 85 ± 11 eV. The X-ray spectrum appears dominated by thermal, Seyfert-like processes, but there are also indications of non-thermal processes. The radio to γ-ray spectral energy distribution can be fit with a single-zone synchrotron-self Compton model, with no need for an additional thermal component.

Conclusions. We suggest a hybrid scenario to explain the broad-band emission, including a thermal component (iron line, reflection) that dominates in the X-ray regime and a non-thermal one to explain the spectral energy distribution.