Abstract
We present the results of simultaneous optical multi-color observations of BL Lac object 0716+714 in November 2014 and February 2016. The intra-day variability (IDV) varies from 0.04 to 0.3 mags. Both achromatic and bluer-when-brighter (BWB) color behaviors were detected. A probable quasi-periodic oscillation overlapping on a significant flare was also observed. We used the interpolated cross-correlation function to calculate time lags between light curves in different bands. Variations in the B and R lagging behind that in the I band were found, which corresponds with anti-clockwise loops on the color-magnitude diagrams.
Highlights
S5 0716+714 (RA = 07:21:53.4, Dec = 71:20:36, epoch = J2000) is one of the brightest BL Lac objects in the northern sky
To verify the intra-day variability (IDV) of S5 0716+714, we adopted two very robust statistical tests recommended by de Diego [7]: one-way analysis of variance (ANOVA) and χ2 test
All 15 light curves pass the one-way ANOVA test and 13 light curves pass the χ2 test. This incompatibility can be ascribed to the discrepancy of power of these methods, we can conclude that IDV can be found in all data we observed
Summary
It’s redshift was estimated by Nilsson et al [1] as z = 0.31 ± 0.008, and recently limited by Danforth et al [2] as 0.2315 < z < 0.322 It is one of the best-studied low-frequency-peaked BL Lac object (LBL) with violent variations at different wavelengths from radio to γ-ray and on different time scales from several minutes to decades. A loop-like path in the color-magnitude diagram can be caused by acceleration and cooling processes of particles in the jet (e.g., [3,4]). It is consistent with time lags between different optical bands. Aiming to find these lags precisely, we monitored S5 0716+714 with high temporal resolution
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