... blazars

Table 5 is only available in electronic form at http://www.edpsciences.org

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... available

at http://tartarus.gsfc.nasa.gov/

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...

We have verified that this choice does not introduce a bias towards particularly faint states of the sources (for which lower statistics could yield larger error bars and better $\chi^2$) nor towards particularly high states (for which a better statistics could yield lower values of the reduced $\chi^2$ due to the increased number of degrees of freedom).

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