AN EXCESS OF MG-II ABSORBERS IN BL-LACERTAE OBJECTS

Three Mg II absorbers are presented, one of which is new (z = 1.340 in S5 0454+844), bringing the total number of Mg Ir systems in the 1 Jy radio-selected BL Lac sample to 10. Five of the 10 absorption systems are at W-lambda > 1 Angstrom; this is a factor of 4-5 greater than the number expected based upon quasar sight lines and is 2.5-3 sigma grea ter than the expectation value. Interpretations of this possible exces s include either that some of the Mg II absorbers might be intrinsic t o the BL Lac or that there is a correlation between the presence of ab sorbing gas in the foreground and the nearly featureless spectra of th ese BL Lac objects compared to quasars. Such a correlation can be crea ted by gravitational microlensing as suggested by Ostriker & Vietri. T he similarity between the optical spectra of BL Lac objects with Mg II absorption and the spectrum of the gamma-ray burst source GRB 970508 suggests that models of gamma-ray bursts as microlensed AGNs should be investigated.