The Time Scales of the Optical Variability of Blazars.IV.OI 090.4

Optical photometric observations of the blazar OI 090.4 are presented as part of an ongoing study of variations in blazars occurring on timescales of minutes to hours, which has been termed microvariability. The observations presented here reveal the existence of such variability for this blazar and provide further evidence of the class-wide nature of this phenomenon. Timescales as short as these provide important clues about the nature of blazars, and a discussion of the types of possible mechanisms responsible for producing these variations is given.