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Emission-line variability during a nonthermal outburst in the gamma-ray bright quasar 1156+295

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Emission-line variability during a nonthermal outburst in the gamma-ray bright quasar 1156+295 Hallum, Melissa K.; Jorstad, Svetlana G.; Larionov, Valeri M.; Marscher, Alan P.; Joshi, Manasvita; Weaver, Zachary R.; Williamson, Karen E.; Agudo, Iván; Borman, George A.; Casadio, Carolina; Fuentes, Antonio; Grishina, Tatiana S.; Kopatskaya, Evgenia N.; Larionova, Elena G.; Larionova, Liyudmila V.; Morozova, Daria A.; Nikiforova, Anna A.; Savchenko, Sergey S.; Troitsky, Ivan S.; Troitskaya, Yulia V.; Vasilyev, Andrey A. We present multi-epoch optical spectra of the γ-ray bright blazar 1156+295 (4C +29.45, Ton 599) obtained with the 4.3 m Lowell Discovery Telescope. During a multiwavelength outburst in late 2017, when the γ-ray flux increased to 2.5 × 10−6 phot cm−2 s−1 and the quasar was first detected at energies ≥100 GeV, the flux of the Mg ii λ2798 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 ≲2 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 γ-ray energies by relativistic electrons in the jet.

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