# The optical microvariability and spectral changes of the BL Lacertae object S5 0716+714

## TL;DR

This study monitored the optical microvariability of BL Lac object S5 0716+714 over several months, observing rapid flares, spectral changes, and potential time lags, providing insights into its variability mechanisms.

## Contribution

First detailed optical microvariability study of S5 0716+714 with high temporal resolution across multiple bands, revealing spectral behaviors and potential time lags.

## Key findings

- Detected four fast flares with amplitudes up to 0.75 mag.
- Observed bluer-when-brighter chromatism on internight timescales.
- Identified a possible 11-minute time lag between B and I bands.

## Abstract

We monitored the BL Lac object S5 0716+714 in the optical band during October 2008, December 2008 and February 2009 with a best temporal resolution of about 5 minutes in the BVRI bands. Four fast flares were observed with amplitudes ranging from 0.3 to 0.75 mag. The source remained active during the whole monitoring campaign, showing microvariability in all days except for one. The overall variability amplitudes are delta B ~ 0.89 mag, delta V ~ 0.80 mag, delta R ~ 0.73 mag and delta I ~0.51 mag. Typical timescales of microvariability range from 2 to 8 hours. The overall V - R color index ranges from 0.37 to 0.59. Strong bluer- when-brighter chromatism was found on internight timescales. However, different spectral behavior was found on intranight timescales. A possible time lag of ~ 11 mins between B and I bands was found on one night. The shock-in-jet model and geometric effects can be applied to explain the source's intranight behavior.