Bibcode
                                    
                            DOI
                                    
                            Moles, M.; Garcia-Pelayo, J. M.; Masegosa, J.; Aparicio, A.
    Bibliographical reference
                                    Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 58, June 1985, p. 255-263.
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                        6
            
                        1985
            
  Citations
                                    54
                            Refereed citations
                                    53
                            Description
                                    A total of 85 UBVRI observations of BL Lac objects is presented. For
most of them, an average continuum can be traced by means of
well-defined color indices. These continua are always well reproduced by
power laws, strongly supporting the hypothesis of a synchrotron origin
of the radiation output, as well as the conclusion that there is no dust
in such objects. The analysis of the variability leads to a rough
estimate of the value of the magnetic field, which is of the same order
for all the objects, around 0.00003 G. The optical continua can be
considered to correspond to the broken part of the synchrotron spectrum.
Relativistic effects are needed in order to avoid the Compton paradox.