Soft Excess Emission (original) (raw)
Time Lags in Narrow-Line Seyfert 1 Galaxies and the Origin of Their Soft Excess Emission
Progress of Theoretical Physics Supplement, 2007
The origin of soft X-ray excess emission from type 1 active galactic nuclei has remained a major problem for the last two decades. It has not been possible to distinguish alternative models for the soft excess emission despite the excellent data quality provided by XMM-Newton and Chandra. Here we present observations of time lags between the soft and hard band
The contribution of narrow-line Seyfert 1 galaxies to the soft X-ray background
New Astronomy Reviews, 2000
T he contribution of N arrow-Line Seyfert 1 galaxies to the soft X-ray background G .H asi nger a I.Lehm ann a; b M .Schm i dt c J. E.G unn d D. P.Schnei der b R .G i acconi e J.Tr um per f G .Zam orani g a A strophysikal isches InstitutPotsdam ,A n der Sternwarte 16,D-14482 Potsdam , G erm any b D epartm ent ofA stronom y & A strophysics,525 D avey Lab,T he Pennsyl vania State U niversity,
The Central Engines of Narrow‐Line Seyfert 1 Galaxies
The Astrophysical Journal, 2007
It has been suggested that Narrow-Line Seyfert 1 (NLS1) galaxies are evolutionarily young objects, powered by the accretion of gas onto central black holes that are significantly lower in mass than those found in typical broad-line Seyferts. We explore this hypothesis through the analysis of high-spatial resolution, near-IR imaging data obtained in J and K ′ for a sample of 11 NLS1s. Surface brightness profiles are separated into their constituent components using two-dimensional decomposition techniques. By employing the correlation between black-hole mass and host galaxy bulge luminosity, calibrated for near-IR wavelengths using 2MASS data, we determine the mean black-hole mass for our sample to be, in solar units, log(M BH) = 7.9. Using the correlation between the size of the broad-line region and the monochromatic continuum luminosity, we obtain black-hole mass estimates under the assumption that the emission-line gas is in virial equilibrium. The mean black-hole mass derived from this relation is log(M BH) = 6.4. It is found that the estimates obtained from the black-hole mass-bulge luminosity relation are systematically one full order of magnitude larger than those derived from the black-hole mass-broad-line region radius relation. We explore possible causes for this discrepancy in M BH estimates and the ramifications for our understanding of the role played by NLS1s in AGN evolution. Because numerical simulations constrain the start of the AGN duty cycle to a time shortly after a significant gravitational interaction, we examine the morphology and near-IR bulge colors of the NLS1 sample for evidence of recent encounters. The mean bulge color is found to be (J − K s) = +1.85 ± 0.58, which is redder than that of both a matched sample of non-active galaxies and published estimates for broad-line Seyferts. The source of the unusual bulge colors may be an excess of flux, peaking at around 2.2 µm, that has been detected near the centers of some NLS1s such as Mrk 1239. No evidence is found for light asymmetries or an extra stellar component that would indicate NLS1s are young objects. Finally, we postulate that there may be some interesting lines of circumstantial evidence suggesting that secular processes may be relevant in the evolution of NLS1s.
A disc reflection model for ultra-soft narrow-line Seyfert 1 galaxies
Monthly Notices of the Royal Astronomical Society, 2020
We present a detailed analysis of the XMM–Newton observations of five narrow-line Seyfert 1 galaxies (NLS1s). They all show very soft continuum emission in the X-ray band with a photon index of Γ ≳ 2.5. Therefore, they are referred to as ‘ultra-soft’ NLS1s in this paper. By modelling their optical/UV–X-ray spectral energy distribution (SED) with a reflection-based model, we find indications that the disc surface in these ultra-soft NLS1s is in a higher ionization state than other typical Seyfert 1 AGN. Our best-fitting SED models suggest that these five ultra-soft NLS1s have an Eddington ratio of λEdd = 1–20 assuming available black hole mass measurements. In addition, our models infer that a significant fraction of the disc energy in these ultra-soft NLS1s is radiated away in the form of non-thermal emission instead of the thermal emission from the disc. Due to their extreme properties, X-ray observations of these sources in the iron band are particularly challenging. Future observ...
Difference in Narrow Emission Line Spectra of Seyfert 1 and 2 galaxies
2008
In the unification scheme of Seyfert galaxies, a dusty torus blocks the continuum source and broad line region in Seyfert 2 galaxies. However it is not clear whether or not and to what extent the torus affects the narrow line spectra. In this paper, we show that Seyfert 1 and Seyfert 2 galaxies have different distributions on the [O III]/H β vs [N II]/H α diagram (BPT diagram) for narrow lines. Seyfert 2 galaxies display a clear left boundary on the BPT diagram and only 7.3% of them lie on the left. By contrast, Seyfert 1 galaxies do not show such a cutoff and 33.0% of them stand on the left side of the boundary. Among Seyfert 1 galaxies, the distribution varies with the extinction to broad lines. As the extinction increases, the distribution on BPT diagram moves to larger [N II]/H α value. We interpret this as an evidence for the obscuration of inner dense narrow line region by the dusty torus. We also demonstrate that the [O III] and broad line luminosity correlation depends on the extinction of broad lines in the way that high extinction objects have lower uncorrected [O III] luminosities, suggesting that [O III] is partially obscured in these objects. Therefore, using [O III] as an indicator for the nuclear luminosity will systematically under-estimate the nuclear luminosity of Seyfert 2 galaxies.
An absorption origin for the soft excess in Seyfert 1 active galactic nuclei
Monthly Notices of the Royal Astronomical Society, 2007
The soft excess seen in the X-ray spectra of many active galactic nuclei (AGN) can be well modelled by reflection from a partially ionized accretion disc. However, this often requires extreme parameters, both in terms of the underlying space-time and the reflection geometry, and requires that the disc is far from hydrostatic equilibrium. An alternative model uses similarly partially ionized, velocity smeared material but from an accretion disc wind seen in absorption. We explicitly compare these two models for the origin of the soft excess using XMM-Newton data for PG QSOs and narrow-line Seyfert 1 galaxies (NLS1s). We find that while reflection and absorption give comparably good fits to the data, the absorption model allows a much clearer correspondence with the stellar mass black holes. All the objects are high mass accretion rate AGN, so should be analogous to the high/soft and very high states in black hole binaries. The intrinsic spectral indices derived from the absorption model are all consistent with a oneto-one mapping between spectral state and AGN type, with the NLS1s having softer spectra corresponding to the very high state, while the broad-line AGN have = 2 as expected for the high/soft state. By contrast, a few AGN have intrinsically hard spectra with the reflection model. While this supports an absorption interpretation of the soft excess, we note that the required Gaussian velocity dispersion of 0.2c (corresponding to an outflow velocity 0.4c) is too fast for a radiatively driven accretion disc wind and instead requires that the material is entrained in a magnetic outflow (jet). We also use the simultaneous optical monitor data to derive the ratio of disc to total accretion power which is another tracer of spectral state in X-ray binaries. This does not always show that the disc in NLS1s contributes less than 80 per cent of the total power, as expected for a very high state. We suggest that this is an artefact of the standard disc models used to determine the disc luminosity in our fits. The disc seen in the very high state of black hole binaries is often observed to be distorted from the standard shape, and a similar effect in NLS1s could recover the one-to-one mapping between black hole binary spectral state and AGN type.
Astrophysical Journal Supplement Series, 2006
This is the first paper in a series dedicated to the study of the emission-line and continuum properties of narrow line Seyfert 1 galaxies (NLS1s). We carried out a systematic search for NLS1s from objects assigned as "QSOs" or "galaxies" in the spectroscopic sample of the Sloan Digital Sky Survey Data Release 3 (SDSS DR3) by a careful modeling of their emission lines and continua. The result is a uniform sample comprising ∼ 2 000 NLS1. This sample dramatically increases the number of known NLS1 by a factor of ∼ 10 over previous compilations. This paper presents the parameters of the prominent emission lines and continua, which were measured accurately with typical uncertainties < 10%. Taking advantage of such an unprecedented large and uniform sample with accurately measured spectral parameters, we carried out various statistical analysis, some of which were only possible for the first time. The main results found are as follows.
A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies
Astronomy & Astrophysics, 2001
We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1 galaxies (NLS1s) or known to have a broad Balmer component narrower than 2 000 km s −1. Of these, 19 turned out to have been spectroscopically misidentified in previous studies; only 64 of the selected objects are genuine NLS1s. We have spectroscopically observed 59 of them and tried to characterize their Narrow and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components are well fitted by a single Lorentzian profile, confirming previous claims that Lorentzian rather than Gaussian profiles are better suited to reproduce the shape of the NLS1s broad emission lines. This has consequences concerning their FWHMs and line ratios: when the broad Balmer components are fitted with a Lorentzian, most narrow line regions have line ratios typical of Seyfert 2s while, when a Gaussian profile is used for fitting the broad Balmer components, the line ratios are widely scattered in the usual diagnostic diagrams (Veilleux & Osterbrock 1987); moreover, the FWHM of the best fitting Lorentzian is systematically smaller than the FWHM of the Gaussian. We find that, in general, the [O III] lines have a relatively narrow Gaussian profile (∼200-500 km s −1 FWHM) with often, in addition, a second broad (∼500-1 800 km s −1 FWHM), blueshifted Gaussian component. We do not confirm that the [O III] lines are weak in NLS1s. As previously suggested, there is a continuous transition of all properties between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit of 2000 km s −1 used to separate the two species is arbitrary; R4570, the ratio of the Fe II to the Hβ fluxes, could be a physically more meaningful parameter to distinguish them.
Radio and γ-ray loud narrow-line Seyfert 1 galaxies in the spotlight
Proceedings of the International Astronomical Union, 2016
Narrow-line Seyfert 1 (NLS1) galaxies provide us with unique insights into the drivers of AGN activity under extreme conditions. Given their low black hole (BH) masses and near-Eddington accretion rates, they represent a class of galaxies with rapidly growing supermassive BHs in the local universe. Here, we present the results from our multi-frequency radio monitoring of a sample of γ-ray loud NLS1 galaxies (γNLS1s), including systems discovered only recently, and featuring both the nearest and the most distant γNLS1s known to date. We also present high-resolution radio imaging of 1H 0323+342, which is remarkable for its spiral or ring-like host. Finally, we present new radio data of the candidate γ-emitting NLS1 galaxy RX J2314.9+2243, characterized by a very steep radio spectrum, unlike other γNLS1s.