Flare-like Variability of the Mg ii λ2798 Å Emission Line and UV Fe ii Band in the Blazar CTA 102

Abstract

We report on the detection of a statistically significant flare-like event in the Mg II λ 2798Å emission line and the UV Fe II band of CTA 102 during the outburst of autumn 2017. The ratio between the maximum and minimum of λ3000Å continuum flux for the observation period (2010 − 2017) is 179±15. Respectively, the max/min ratios 8.1±10.5 and 34.0±45.5 confirmed the variability of the Mg II emission line and of the Fe II band. The highest levels of emission lines fluxes recorded coincide with a superluminal jet component traversing through a stationary component located at ∼0.1 mas from the 43 GHz core. Additionally, comparing the Mg II line profile in the minimum of activity against the one in the maximum, we found that the latter is broader and blue-shifted. As a result of these findings, we can conclude that the non-thermal continuum emission produced by material in the jet moving at relativistic speeds is related to the broad emission line fluctuations. In consequence, these fluctuations are also linked to the presence of broad-line region (BLR) clouds located at ∼25 pc from the central engine, outside from the inner parsec, where the canonical BLR is located. Our results suggest that during strong activity in CTA 102, the source of non-thermal emission and broadline clouds outside the inner parsec introduces uncertainties in the estimates of black hole (BH) mass. Therefore, it is important to estimate the BH mass, using single-epoch or reverberation mapping techniques, only with spectra where the continuum luminosity is dominated by the accretion disk.

Multiwavelength analysis and the difference in the behavior of the spectral features during the 2010 and 2014 flaring periods of the blazar 3C 454.3

“…The highest levels of the Mg II λ2798 Å emission line and the UV Fe II band fluxes and the 2010 gammaray outburst happen at the time when a jet component passes through or is ejected from the radio core of 3C 454.3. Similar behavior was observed for CTA 102 but in greater scale (Chavushyan et al 2020), the ratio between the maximum and minimum of λ3000 Å continuum flux was ∼ 179, and for the Mg II emission line and the UV Fe II fluxes, the ratios were ∼ 8 and ∼ 34, respectively.…”

“…Lastly, the error for the estimation of the λ3000 Å continuum flux was calculated taking the root mean square of the iron-subtracted spectrum around λ3000±50 Å. For further details, see León-Tavares et al (2013); Chavushyan et al (2020). A sample of the measured fluxes and errors is displayed in Table 1.…”

“…Another tool that can help to understand what was happening during these major events is the Non-Thermal Dominance parameter (NTD, Shaw et al 2012;Patiño-Álvarez et al 2016;Chavushyan et al 2020). The calculation of the NTD, as its name suggests, constitutes a method to find out if there is a non-thermal contribution (the jet as the source) to the continuum emission.…”

The observability of plasmoid-powered $γ$-ray flares with the Fermi Large Area Telescope

“…This is about 20 times brighter than the Hβ luminosity observed from 3C 279 (Liu et al 2006). This discrepancy might be explained by a brightening of the BLR; flare-like activity of emission lines from the BLR has been found in coincidence with enhanced non-thermal emission from the jet of 3C 454.3 and CTA 102 (León-Tavares et al 2013;Chavushyan et al 2020). The flux from the Mg-II line was found to vary by a factor of a few, whereas the ratio between maximum and minimum flux for the Fe-II line in CTA 102 reached a value of 34.…”

“…The flux from the Mg-II line was found to vary by a factor of a few, whereas the ratio between maximum and minimum flux for the Fe-II line in CTA 102 reached a value of 34. Additionally, Chavushyan et al (2020) interpret their results as evidence for an additional more extended BLR component which would provide an additional source of external photons. Being more diluted (u ext ∝ R −2 ext ) though, this extra BLR component would not be an important source of seed photons for inverse Compton scattering.…”