The optical variability properties of flat spectrum radio quasar 3C 454.3

•The long-term quasi-simultaneous observation data in BVRI bands are collected.•The intraday and long-term variability timescales were investigated by means of SF and χ2χ2 methods.•We found that the optical spectrum has clear different trends when the source is in different state.•The variability properties of 3C 454.3 in optical energy region are comprehensive understanding.

The optical variability and property of color index of the flat spectrum radio quasar object 3C 454.3 have been studied. The source exhibits strong variability both in intraday and long-term timescale. The χ2χ2 test suggests that 171 out of 285 nights in R band present intraday variability, and the typical intraday timescale is 0.02–0.1 day. The strong correlation between color index B–I and the brightness in I band imply that there is a general redder-when-brighter trend in faint state of I >> 14 mag, in the sense that the spectrum steepens as the brightness increases. However, when the source is in the bright state, I << 14 mag, the spectrum remains unchanged. Using the minimum intraday timescale of 0.02±0.010.02±0.01 day and the typical Doppler factor δD=25δD=25, the radius of emission region of 3C 454.3 is estimated to be (7.0±3.5)×1014(7.0±3.5)×1014 cm, and the upper limit of the central black hole is estimated to be M=(1.9±1.0)×1010M⊙.