A Search for Intraday Variability in the Blazar PKS 2005−489

Rapid, multicolor optical monitoring carried out for a multiwavelength campaign during 2000 August 22–27 is presented for the bright and variable BL Lac object PKS 2005-489. Previous multiwavelength monitoring campaigns of PKS 2005-489 have found complex variability behavior both in flux density and in broadband spectrum, with different modes and timescales from days to hours. During this campaign PKS 2005-489 was observed to be in an unusual state, bright in the optical but faint in the X-ray, just prior to an X-ray flare that began on 2000 September 2. PKS 2005-489 was also observed to have a flatter optical spectrum than in prior epochs. A linear increase in optical flux density was observed during the first 5.2 days of the campaign. However, intraday and color variability were not detected. The large discrepancy between the ratio of X-ray to optical flux density observed during this campaign and that observed in prior epochs indicates a lack of long-term correlation between the two wave bands, and it illustrates that simple particle injection events in the jet are insufficient to explain the long-term variability behavior of this object. Twenty-three in-field standard stars are identified for future optical monitoring programs.