2021MNRAS.504L..22R

Radio and γ-ray loud narrow-line Seyfert 1 galaxies (NLS1s) are unique objects to study the formation and evolution of relativistic jets, as they are believed to have high accretion rates and powered by low mass black holes contrary to that known for blazars. However, only about a dozen γ-ray-detected NLS1s (γ-NLS1s) are known to date and all of them are at z <= 1. Here, we report the identification of a new γ-ray-emitting NLS1 TXS 1206 + 549 at z = 1.344. A near-infrared spectrum taken with the SubaruTelescope showed H β emission line with FWHM of 1194 ± 77 km s^–1 and weak [O III] emission line but no optical Fe II lines, due to the limited wavelength coverage and poor signal-to-noise ratio. However, UV Fe II lines are present in the SDSS optical spectrum. The source is very radio-loud, unresolved, and has a flat radio spectrum. The broad-band spectral energy distribution of the source has the typical two hump structure shown by blazars and other γ-NLS1s. The source exhibits strong variability at all wavelengths such as the optical, infrared, and γ-ray bands. All these observed characteristics show that TXS 1206 + 549 is the most distant γ-NLS1 known to date.