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We present multi-epoch optical spectra of the $\gamma$-ray bright blazar1156+295 (4C +29.45, Ton 599) obtained with the 4.3~m Lowell DiscoveryTelescope. 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 fluxof the Mg II $\lambda 2798$ emission line changed, as did that of the Feemission complex at shorter wavelengths. These emission line fluxes increasedalong with the highly polarized optical continuum flux, which is presumablysynchrotron 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-lineradiation from such clouds, which are located outside the canonicalaccretion-disk related broad-line region, may be a primary source of seedphotons that are up-scattered to $\gamma$-ray energies by relativisticelectrons in the jet.

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