Multicolor Optical Monitoring of the BL Lacertae Object S5 0716+714 during the 2012 Outburst

Abstract

We monitored the BL Lacertae object S5 0716+714 in the optical bands during 2012 January and February with long time spans on intraday timescales (>5 hr) and high time resolutions. During this monitoring period, the object shows violent flaring activity in both short and intraday timescales. The object has a high duty cycle. The light curves detected as intraday variability show variability of various shapes. The variability amplitude is from 12.81% to 33.22%, and the average value is 19.92% ± 5.87%. The overall magnitude variabilities are , , ,  and  . During the observations, the average change rate is Mag/h during the ascent and Mag/h during the descent. However, different cases are found on certain nights. There are good interband correlations but no significant time lags for intraday and short timescales. The results of the autocorrelation function show that the variability timescales range from 0.054 to 0.134 day. Most nights show a bluer-when-brighter (BWB) chromatic trend, a weak redder-when-brighter (RWB) trend is found, and a few nights show no correlation between magnitude and color index. The BWB trend appears in short timescales. During the flare, the spectral index exhibits a clockwise loop for internights. A shock-in-jet model and the shock wave propagating along a helical path are likely to explain the variability and color index variability.