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

TL;DR

This study analyzes multi-wavelength observations of the quasar 1633+382, revealing correlated long-term activity and time lags between radio and gamma-ray emissions, indicating different emission regions.

Contribution

It provides a detailed phenomenological analysis of the variability and correlations across multiple bands in 1633+382, with new insights into emission region locations.

Findings

Long-term activity increase in radio and other bands.

Radio and gamma-ray fluxes are correlated with time lags.

Emission regions are separated by approximately 40 parsecs.

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 radio, optical, X-rays and $\gamma-$rays carried out between the period 2012 March - 2015 August. The monitoring of this source reveals a significant long-lived increase in its activity since approximately two years in the radio bands, which correlates with a similar increase on all other bands from sub-millimeter 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 (DCF) indicates time lags smaller than the $\sim40$ days uncertainties among both radio bands and also high-energy bands, and a time lag of $\sim$70 days, with $\gamma-$rays leading radio. We interpret that the high-energy and radio fluxes are arising from different emitting regions, located at $1\pm12$ and $40\pm13$ pc from the central engine respectively.