Multiwavelength Variation Phenomena of PKS 0735+178 on Diverse Timescales

Abstract The BL Lac object PKS 0735+178 has shown some complex multiwavelength variation phenomena in previous studies, especially its color behavior. Bluer-when-brighter, redder-when-brighter, and achromatic behavior were all found to be possible long-term trends of 0735+178. In this work, we collected data on 0735+178, also performed a multicolor optical monitoring intraday timescales. Intraday variability was detected one night. On long timescales, 22 day time lag between the R ? -ray bands. results cross-correlation analysis exhibited strong correlations various bands both However, only mild correlation -band light curves, which could interpreted as different emission mechanisms for emissions. showed significant harder-when-brighter (HWB) band, is consistent with observed bluer-when-brighter (BWB) trend We that HWB BWB will enhanced during active states, historical low state. Such phenomenon indicates special activity-dependent it well by jet model.