Bibcode
                                    
                            Perez-Fournon, I.; Biermann, P.
    Bibliographical reference
                                    Astronomy and Astrophysics (ISSN 0004-6361), vol. 130, no. 2, Jan. 1984, p. L13-L15. Sponsorship: Deutsche Forschungsgemeinschaft.
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                        1
            
                        1984
            
  Citations
                                    22
                            Refereed citations
                                    14
                            Description
                                    The evidence is noted that (1) a flux density limited complete sample of
X-ray emitting BL Lac type sources is now available from Schwartz and Ku
(1983), that (2) the radio through X-ray emission of BL Lac type sources
is most easily interpreted as nonthermal emission from a
relativistically boosted jet pointed close to the line of sight and that
(3) all galaxies identified with BL Lacs are of giant elliptical type.
From this, a space density of the parent population of BL Lacs is
derived, elliptical galaxies with relativistically boosted jets not
generally pointed at the observer. This space density is remarkably
close to that of bright elliptical galaxies and suggests that these
galaxies constitute the parent population for BL Lacs.