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Paper: HST Observations and the BL Lac/FR I/ Unifying Model
Volume: 159, BL Lac Phenomenon
Page: 355
Authors: Celotti, Annalisa; Capetti, Alessandro
Abstract: HST observations provide a novel way of testing unified models for FR I and BL Lacs through the direct comparison of any anisotropic optical nuclear emission present in both systems. Furthermore they revealed the presence of extended nuclear disks in FR I which might provide information on the jet orientation. We selected 5 FR I which show nuclear discs. At their center an unresolved nuclear source is present. We compared its luminosity with the optical core luminosity of BL Lacs selected for having similar host galaxy magnitude and extended radio luminosity. The BL Lac/FR I core luminosity ratio ranges between 200 and 300000 and shows a clear trend with the orientation of the radio galaxies with respect to the line of sight. This behavior is quantitatively consistent with a scenario in which the emission in the FR I and BL Lac is dominated by radiation beamed with Doppler factors 5 - 10, thus supporting the proposed unification scheme.
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