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

Abstract

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 gamma-ray-bright active galactic nuclei (iMOGABA) program combined with additional observations in the radio, optical, X-rays, and gamma-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 gamma-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 similar to 40 days among both radio bands and high-energy bands, and a time lag of similar to 70 days, with gamma-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.