Spectral energy distributions of FR I nuclei and the FR I/BL Lac unifying model

We consider archival ROSAT and Hubble Space Telescope (HST) observations of five FR I radio galaxies and isolate their nuclear emission from that of t he host galaxy. This enables us to determine the spectral energy distributi ons (SEDs) of their nuclei spanning the region from the radio to the X-ray band. They cannot be described as single power laws, but require the presen ce of an emission peak located between the infrared (IR) and soft X-ray ban d. We found consistency between the SED peak position and the values of the broad-band spectral indices of radio galaxies compared with those of BL La cs, once the effects of beaming are properly taken into account. FR I SEDs are thus qualitatively similar to those of BL Lacs, supporting the identifi cation of FR I sources as their misoriented counterparts. No dependence of the shape of the SED on the FR I orientation is found.