Spectroscopic monitoring of the Blazar 3C 454.3

TL;DR

This study presents the first UV spectroscopic monitoring of blazar 3C 454.3 over five years, revealing how emission lines and continuum flux vary and respond during different activity states, including outbursts.

Contribution

It provides new long-term UV spectroscopic data of 3C 454.3, showing the emission line and continuum variability and their correlation, especially during active and quiescent phases.

Findings

MgII flux varies by a factor of ~3, UV continuum by ~14.

MgII emission lines respond proportionally during low activity.

UV FeII flux correlates strongly with continuum flux.

Abstract

We performed an optical spectroscopic monitoring of the blazar 3C 454.3 from September 2003 to July 2008. Sixteen optical spectra were obtained during different runs, which constitute the first spectroscopic monitoring done in the rest-frame UV region (z=0.859). An overall flux variation of the MgII (2800 A) by a factor ~ 3 was observed, while the corresponding UV continuum (F_cont at 3000 A) changed by a factor ~ 14. The MgII emission lines respond proportionally to the continuum variations when the source is in a low-activity state. In contrast, near the optical outbursts detected in 2005 and 2007, the MgII emission lines showed little response to the continuum flux variations. During the monitored period the UV FeII flux changed by a factor ~ 6 and correlated with F_cont (r = 0.92). A negative correlation between EW(Mg II) and F_cont was found, i.e. the so-called "Intrinsic Baldwin Effect".