Nuclear broadband SED of NGC 6251 compiled using multi-epoch data. Radio to optical-UV data are reported in Table 4. Solid black triangles are the total IR flux. The solid IR points are the extrapolated non-thermal synchrotron fluxes given in Leipski et al. (2009). Empty optical-UV data are dereddened (see text). X-ray emission is presented in Sect. 3.2: black dots are for XMM-Netwon data and red from Swift satellite. Black γ-ray points correspond to EGRET flux (Mukherjee et al. 2002). Red γ-ray points are Fermi data (Abdo et al. 2010c). Left panel: the SED is modeled with a one-zone SSC model (solid black line: synchrotron curve, solid red line: IC emission). Right panel: the SED is modeled with the spine-layer model illustrated in Ghisellini et al. (2005). Solid black and red lines reproduce the SSC emission of the layer. Dashed black and red curves are the SSC model for the spine. The long-dashed blue line is the IC emission of the spine synchrotron photons scattered by the layer relativistic electrons.