We performed a long-term optical (B, V, R bands), infra-red (J and K bands) and radio band (15, 22, 37 GHz band) study on the ﬂat spectrum radio quasar, 3C 454.3, using the data collected over a period of more than 8 years (MJD 54500–57500). The temporal variability, spectral properties and inter-waveband correlations were studied by dividing the available data into smaller segments with more regular sampling. This helped us constrain the size and the relative locations of the emission regions for diﬀerent wavebands. Spectral analysis of the source revealed the interplay between the accretion disk and jet emission. The source predominantly showed a redder-when-brighter trend, though we observed a bluer-when-brighter trend at high ﬂux levels which could be signatures of particle acceleration and radiative cooling. Signiﬁcant correlations with near-zero lag were seen between various optical/infra-red bands, indicating that these emission regions are co-spatial. Correlations with a time lag of about 10–100 days are seen between optical/infra-red and radio bands indicating these emissions arise from diﬀerent regions. We also observe the DCF peak lag change from year to year. We try to explain these diﬀerences using a curved jet model where the diﬀerent emission regions have diﬀerent viewing angles resulting in a frequency dependent Doppler factor. This variable Doppler factor model explains the variability timescales and the variation in DCF peak lag between the radio and optical emissions in diﬀerent segments. Lags of 6-180 days are seen between emissions in various radio bands, indicating a core-shift eﬀect.
- galaxies: active
- methods: observational
- quasars: individual (3C 454.3)
- techniques: photometric