The SMARTS Multi-epoch Optical Spectroscopy Atlas (SAMOSA): Using Emission Line Variability to Probe the Location of the Blazar Gamma-emitting Region

TL;DR

This study uses multi-epoch optical spectroscopy of blazars to investigate the relationship between emission line variability and gamma-ray activity, revealing that jet variability is mostly independent of accretion disk activity but sometimes correlates with large gamma-ray flares.

Contribution

It provides new insights into the connection between jet activity and emission line variability, suggesting gamma-ray production can occur within the broad line region during large flares.

Findings

Emission lines are less variable than the continuum in blazars.

Jet variability is generally independent of accretion disk activity.

Some large gamma-ray flares coincide with emission line flares, indicating possible gamma-ray production within the broad line region.

Abstract

We present multi-epoch optical spectroscopy of seven southern Fermi-monitored blazars from 2008 - 2013 using the Small and Medium Aperture Research Telescope System (SMARTS), with supplemental spectroscopy and polarization data from the Steward Observatory. We find that the emission lines are much less variable than the continuum; 4 of 7 blazars had no detectable emission line variability over the 5 years. This is consistent with photoionization primarily by an accretion disk, allowing us to use the lines as a probe of disk activity. Comparing optical emission line flux with Fermi $\gamma$-ray flux and optical polarized flux, we investigate whether relativistic jet variability is related to the accretion flow. In general, we see no such dependence, suggesting the jet variability is likely caused by internal processes like turbulence or shock acceleration rather than a variable accretion rate. However, three sources showed statistically significant emission line flares in close temporal proximity to very large Fermi $\gamma$-ray flares. While we do not have sufficient emission line data to quantitatively assess their correlation with the $\gamma$-ray flux, it appears that in some cases, the jet might provide additional photoionizing flux to the broad line region, which implies some gamma-rays are produced within the broad line region, at least for these large flares.