Exploring the Variability of the Flat Spectrum Radio Source 1633+382. I. Phenomenology of the Light Curves

We present multi-frequency simultaneous VLBI radio observations of the flat spectrum radio quasar 1633+382 (4C 38.41) as part of the interferometric monitoring of γ-ray-bright active galactic nuclei (iMOGABA) program combined with additional observations in the radio, optical, X-rays, and γ-rays carried out during the period 2012 March–2015 August. The monitoring of this source reveals a significant long-lived increase in its activity for approximately two years in the radio bands, which correlates with a similar increase in all other bands from submillimeter to γ-rays. A significant correlation is also found between radio fluxes and simultaneous spectral indices during this period. The study of the discrete correlation function indicates time lags smaller than the uncertainties of ∼40 days among both radio bands and high-energy bands, and a time lag of ∼70 days, with γ-rays leading radio emission. We interpret this as showing that the high-energy and radio fluxes arise from different emitting regions, located at 1 ± 13 and 40 ± 13 pc from the central engine respectively.