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Register a new userBroadband spectral study of the jet-disc emission in the radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342
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We present a broadband spectral study of the radio-loud narrow-line Seyfert 1 galaxy 1H~0323+342 based on multi-epoch observations performed with NuSTAR 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 broadband spectra and to disentangle the disk/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 3keV and extrapolated to lower energies. The joint spectral analysis of the three datasets above 3keV with this model resulted in a high black hole spin ($a>0.9$) and moderate reflection fraction $Rsim 0.5$. The optxagnf model fitted to the two simultaneous datasets resulted in an excess emission in the 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 $Gamma sim 1.8$, a blurred reflection component with $Rsim 0.5$, Comptonised disk emission as the soft X-ray excess, optical/UV emission from a standard accretion disk around a black hole of mass $sim 10^7{rm M_{odot}}$ and a steep power law ($Gamma sim 3-3.5$) component, most likely the jet emission in the UV band. The fractional RMS variability spectra suggest that both the soft excess and the powerlaw component are variable in nature.
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The supermassive black holes (SMBHs) of narrow-line Seyfert 1 galaxies (NLS1s) are at the lowest end of mass function of active galactic nuclei (AGNs) and preferentially reside in late-type host galaxies with pseudobulges, which are thought to be formed by internal secular evolution. On the other hand, the population of radio-loud NLS1s presents a challenge for the relativistic jet paradigm that powerful radio jets are exclusively associated with very high mass SMBHs in elliptical hosts, which are built-up through galaxy mergers. We investigated distorted radio structures associated with the nearest gamma-ray emitting, radio-loud NLS1 1H 0323+342. This provides supporting evidence for the merger hypothesis based on the past optical/near-infrared observations of its host galaxy. The anomalous radio morphology consists of two different structures, the inner curved structure of currently active jet and the outer linear structure of low-brightness relics. Such a coexistence might be indicative of the stage of an established black hole binary with precession before the black holes coalesce in the galaxy merger process. 1H 0323+342 and other radio-loud NLS1s under galaxy interactions may be extreme objects on the evolutionary path from radio-quiet NLS1s to normal Seyfert galaxies with larger SMBHs in classical bulges through mergers and merger-induced jet phases.
The detection of several radio-loud narrow-line Seyfert 1 (NLS1) galaxies by the Fermi Gamma-Ray Space Telescope hints at the existence of a rare, new class of gamma-ray emitting active galactic nuclei with low black hole masses. Like flat spectrum radio quasars (FSRQs), their gamma-ray emission is thought to be produced via the external Compton mechanism whereby relativistic jet electrons upscatter a photon field external to the jet, e.g. from the accretion disc, broad line region (BLR) and dusty torus, to higher energies. Here we study the origin of the gamma-ray emission in the lowest-redshift candidate among the currently-known gamma-ray emitting NLS1s, 1H 0323+342, and take a new approach. We observationally constrain the external photon field using quasi-simultaneous near-IR, optical and X-ray spectroscopy. Applying a one-zone leptonic jet model, we simulate the range of jet parameters for which this photon field, when Compton scattered to higher energies, can explain the gamma-ray emission. We find that the site of the gamma-ray emission lies well within the BLR and that the seed photons mainly originate from the accretion disc. The jet power that we determine, $1.0 times 10^{45}$ erg s$^{-1}$, is approximately half the accretion disc luminosity. We show that this object is not simply a low-mass FSRQ, its jet is intrinsically less powerful than predicted by scaling a typical FSRQ jet by black hole mass and accretion rate. That gamma-ray emitting NLS1s appear to host underpowered jets may go some way to explaining why so few have been detected to date.
We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multi-frequency Very Long Baseline Array observations. This source is known as the nearest $gamma$-ray emitting radio-loud narrow-line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating the jet being continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical-like shape. The location of the collimation break is coincident with a bright quasi-stationary feature at 7 mas from core (corresponding to a deprojected distance of the order of $sim$100pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting the coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy $gamma$-ray flares detected by the Fermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile between the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial on this source and NLS1s in general.
We made simultaneous single-dish and very long baseline interferometer (VLBI) observations of a narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342, showing gamma-ray activity revealed by Fermi/LAT observations. We found significant variation of the total flux density at 8 GHz on the time scale of one month by the single-dish monitoring. The total flux density varied by 5.5% in 32 days, which is comparable to the gamma-ray variability time scale, corresponding to the variability brightness temperature of $7.0 times 10^{11}$ K. The source consists of central and southeastern components on the parsec (pc) scale. The flux of only the central component decreased in the same way as the total flux density, indicating that the short-term radio variability, and probably the gamma-ray emitting region, is associated with this component. From the VLBI observations we obtained the brightness temperatures of greater than $(5.2 pm 0.3) times 10^{10}$ K, and derived the equipartition Doppler factor of greater than 1.7, the variability Doppler factor of 2.2, and the 8 GHz radio power of $10^{24.6}$ W Hz$^{-1}$. Combining them we conclude that acceleration of radio jets and creation of high-energy particles are ongoing in the central engine, and that the apparent very radio-loud feature of the source is due to the Doppler-boosting effect, resulting in the intrinsic radio loudness to be an order of magnitude smaller than the observed values. We also conclude that the pc-scale jet represents recurrent activity from the the spectral fitting and the estimated kinematic age of pc- and kpc-scale extended components with different position angle.
We report the discovery of a local convergence of a jet cross section in the quasi-stationary jet feature in the gamma-ray-emitting narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342. The convergence site is located at approximately 7 mas (corresponding to the order of 100 pc in deprojection) from the central engine. We also found limb-brightened jet structures at both the upstream and downstream of the convergence site. We propose that the quasi-stationary feature showing the jet convergence and limb-brightening occurs as a consequence of recollimation shock in the relativistic jets. The quasi-stationary feature is one of the possible gamma-ray-emitting sites in this NLS1, in analogy with the HST-1 complex in the M87 jet. Monitoring observations have revealed that superluminal components passed through the convergence site and the peak intensity of the quasi-stationary feature, which showed apparent coincidences with the timing of observed gamma-ray activities.
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