Broad-band spectral study of the jet-disc emission in the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342

We present a broad-band spectral study of the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342 based on multi-epoch observations performed with Nuclear Spectroscopic Telescope Array on 2014 March 15, and two simultaneous observations performed with Suzaku and Swift on 2009 July 26 and 2013 March 1. We found the presence of a strong soft X-ray excess emission, a broad but weak Fe line and hard X-ray excess emission. We used the blurred reflection (relxill) and the intrinsic disc Comptonization (optxagnf), two physically motivated models, to describe the broad-band spectra and to disentangle the disc/corona and jet emission. The relxill model is mainly constrained by the strong soft X-ray excess although the model failed to predict this excess when fitted above 3 keV and extrapolated to lower energies. The joint spectral analysis of the three data sets above 3 keV with this model resulted in a high black hole spin (a > 0.9) and moderate reflection fraction R ∼ 0.5. The optxagnf model fitted to the two simultaneous data sets resulted in an excess emission in the ultraviolet (UV) band. The simultaneous UV-to-hard X-ray spectra of 1H 0323+342 are best described by a model consisting of a primary X-ray power-law continuum with Γ ∼ 1.8, a blurred reflection component with R ∼ 0.5, Comptonized disc emission as the soft X-ray excess, optical/UV emission from a standard accretion disc around a black hole of mass ∼10⁷M_⊙ and a steep power law (Γ ∼ 3-3.5) component, most likely the jet emission in the UV band. The fractional rms variability spectra suggest that both the soft excess and the power-law component are variable in nature.