H0323+022: A New BL Lacertae Object with Extremely Rapid Variability

H0323+022 is a highly variable X-ray source discovered in the HEAO 1 all-sky survey coincident with a 16th mag stellar object. Optical nebulosity around the object strongly suggests that it is a BL Lac object. This paper presents the results of a multiband, multiepoch series of observations that demonstrate beyond reasonable doubt that H0323+022 is a remarkably variable BL Lac object. The optical nebulosity around the stellar object is confirmed, the stellar optical radiation is polarized, and the radio characteristics and the overall electromagnetic spectrum resemble those of other BL Lac objects. Variability is seen in all bands, including radio and broad-band optical variations in days, optical polarization changes on time scales of tens of minutes, and X-ray changes on time scales of ≡30 s. H0323+022 is thus an active galactic nucleus with much of the observed emission emerging from a region ⪉10¹² - 10¹⁴cm in size.