# Multi-color optical monitoring of the BL Lacertae object S5 0716+714 during the 2012 outburst

## TL;DR

This study presents detailed optical monitoring of the BL Lac object S5 0716+714 during a 2012 outburst, revealing rapid variability, color changes, and potential shock-in-jet mechanisms.

## Contribution

First high-resolution, multi-band optical monitoring of S5 0716+714 during its 2012 outburst, analyzing intraday variability and chromatic trends with implications for jet models.

## Key findings

- Detected intraday variability with amplitudes up to 33.22%
- Observed bluer-when-brighter chromatic trend in short timescales
- Identified variability timescales from 0.054 to 0.134 days

## 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 $19.92\pm5.87$ per cent. The overall magnitude variabilities are $\bigtriangleup B=1^{\rm m}.24$, $\bigtriangleup V=1^{\rm m}.42$, $\bigtriangleup R=1^{\rm m}.3$, $\bigtriangleup I=1^{\rm m}.23$ respectively. During the observations, the average change rate is $<CR>=0.035\pm0.009$ Mag/h during the ascent and $<CR>=0.035\pm0.014$ 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.