Multicolor Optical Monitoring of the Quasar 3C 273 from 2005 to 2016

Abstract

We have monitored the quasar 3C 273 in the optical V , R , and I bands from 2005 to 2016. Intraday variability (IDV) is detected on seven nights. The variability amplitudes on most of the nights are less than 10%, and on four nights, more than 20%. When considering the nights with time spans >4 hr, the duty cycle (DC) is 14.17%. Over the 12 years, the overall magnitude and color index variabilities are , , , and , respectively. The largest clear IDV has an amplitude of 42% over just 5.8 minutes, and the weakest detected IDV is 5.4% over 175 minutes. The BWB (bluer when brighter) chromatic trend is dominant for 3C 273 and appears at different flux levels on intraday timescales. The BWB trend exists for short-term timescales and intermediate-term timescales but different timescales have different correlations. There is no BWB trend for our whole time-series data sets. A significant anticorrelation between the BWB trend and length of timescales is found. Combining with V -band data from previous works, we find a possible quasi-periodicity of P  = 3918 ± 1112 days. The possible explanations for the observed variability, BWB chromatic trend, and periodicity are discussed.