Exploring the Variability of the Flat Spectrum Radio Source 1633+382. II: Physical Properties

TL;DR

This study investigates the physical properties and variability of the flat spectrum radio quasar 1633+382 during gamma-ray flares, revealing correlations between radio flux, spectral changes, and jet component ejections, supporting shock-in-jet models.

Contribution

It provides detailed multi-frequency VLBI observations linking gamma-ray flares with jet component ejections and spectral evolution, offering insights into the flare mechanisms in 1633+382.

Findings

Gamma-ray flares coincide with ejection of new VLBI components.

Spectral energy distribution shows higher turnover frequency post-flare.

Magnetic fields are particle dominated and do not change dramatically during flares.

Abstract

The flat spectrum radio quasar 1633+382 (4C~38.41) showed a significant increase of its radio flux density during the period 2012 March - 2015 August which correlates with gamma-ray flaring activity. Multi-frequency simultaneous VLBI observations were conducted as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program and supplemented with additional radio monitoring observations with the OVRO 40m telescope, the Boston University VLBI program, and the Submillimeter Array. The epochs of the maxima for the two largest gamma-ray flares coincide with the ejection of two respective new VLBI components. Analysis of the spectral energy distribution indicates a higher turnover frequency after the flaring events. The evolution of the flare in the turnover frequency - turnover flux density plane probes the adiabatic losses in agreement with the shock-in-jet model. Derived synchrotron self absorption magnetic fields, of the order of 0.1mG, do not seem to dramatically change during the flares, and are much smaller, by a factor $10^4$, than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle dominated emitting region.