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

Abstract

We have 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 both in short and intraday timescales. The object has high value of duty cycle. The light curves detected as intraday variability (IDV) show variability of various shapes. The variability amplitude is from 12.81 per cent to 33.22 per cent, and the average value 19.92 ± 5.87 per cent. The overall magnitude variabilities are △B = 1 m .24, △V = 1 m .42, △R = 1 m .3, △I = 1 m .23 respectively. During the observations, the average change rate is < CR >= 0.035 ± 0.009 Mag/h during the ascent and < CR >= 0.035 ± 0.014 Mag/h during the descent. However, different cases are found on certain nights. There are good inter-bands correlations but not significant time lags for intraday and short timescales. The results of the autocorrelation function show that the variability timescales range from 0.054 day to 0.134 day. Most of nights show bluer when brighter (BWB) chromatic trend; a weak redder with brighter (RWB) trend is found; a few nights show no correlations between magnitude and color index. The BWB trend appears in the short timescales. During the flare the spectral index exhibits a clockwise loop for inter-nights. A shock-in-jet model and the shock wave propagating along a helical path are likely to explain the variability and color index variability.

Optical Quasi-periodic Oscillation of the BL Lacertae Object S5 0716+714 during the Faint State

“…This is a new result which further confirms the result of Gupta et al (2009). The Amp is 4.29% and the magnitude is 13 m .43 on this night that has low variability amplitude and flux level (Dai et al 2015;Hong et al 2017). For IDV of blazar, there are two main mechanisms (intrinsic and extrinsic origins) to explain it (e.g., Xiong et al 2017).…”

“…The specific formulas and variability criterion about the two statistical techniques are seen in these references (e.g., de Diego 2010;Goyal et al 2012;Hu et al 2014;Agarwal & Gupta 2015;Dai et al 2015;Xiong et al 2016Xiong et al , 2017Hong et al 2017). The BL Lac object is considered as variability (V) if the light curve satisfies the two criteria of F -test and ANOVA, probably variable (PV) if only one of the above two criteria is satisfied, and non-variable (N) if none of the criteria are met.…”

“…But extrinsic mechanisms can not explain the origin of the IDV in the optical band (Heeschen et al 1987;Agarwal & Gupta 2015). The IDV/short variability is often explained by the shock-in-jet model (Marscher & Gear 1985;Hu et al 2014;Dai et al 2015;Xiong et al 2016Xiong et al , 2017Hong et al 2017). The changes of relativistic jet always dominate the IDV for blazars in a high state while the origin of IDV can be explained by accretion disk variability in a low state (Xiong et al 2016).…”

“…In order to explore mechanism of variability, we monitored many radio loud AGNs using the 2.4 m, 1.02 m and 60 cm optical telescopes located at the Yunnan Astronomical Observatories (YAO) of Chinese Academy of Sciences of China from 2005 to 2012 (e.g., Liao -5 -et al 2014;Xiong et al 2016Xiong et al , 2017Wang et al 2017;Guo et al 2017;Hong et al 2017).…”

“…Signals of QPOs still need to further be confirmed for them. S5 0716+714 is one of the best studied sources across the electromagnetic spectrum due to high variability with very high duty cycle of IDV (Hong et al 2017 and therein references). It is classified as an intermediate-synchrotron-peaked BL Lac object, which has featureless optical continuum (Abdo et al 2010;Gupta et al 2008).…”