Emission Line Variability during a Nonthermal Outburst in the Gamma-Ray Bright Quasar 1156+295

TL;DR

This study observes emission line variability in the gamma-ray bright quasar 1156+295 during a 2017 outburst, linking changes in emission lines to jet activity and suggesting proximity of line-emitting clouds to the jet.

Contribution

First multi-epoch optical spectra during a gamma-ray outburst reveal emission line variability correlated with jet activity, indicating clouds near the jet as a potential seed photon source.

Findings

Emission lines increased with polarized optical flux

Line-emitting clouds are near the relativistic jet

Emission line variability occurs within approximately 2 weeks

Abstract

We present multi-epoch optical spectra of the $\gamma$-ray bright blazar 1156+295 (4C +29.45, Ton 599) obtained with the 4.3~m Lowell Discovery Telescope. During a multi-wavelength outburst in late 2017, when the $\gamma$-ray flux increased to $2.5\times 10^{-6} \; \rm phot\; cm^{-2}\; s^{-1}$ and the quasar was first detected at energies $\geq100$ GeV, the flux of the Mg II $\lambda 2798$ emission line changed, as did that of the Fe emission complex at shorter wavelengths. These emission line fluxes increased along with the highly polarized optical continuum flux, which is presumably synchrotron radiation from the relativistic jet, with a relative time delay of $\lesssim2$ weeks. This implies that the line-emitting clouds lie near the jet, which points almost directly toward the line of sight. The emission-line radiation from such clouds, which are located outside the canonical accretion-disk related broad-line region, may be a primary source of seed photons that are up-scattered to $\gamma$-ray energies by relativistic electrons in the jet.