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...

Properties of Narrow line Seyfert 1 galaxies

Bulletin de la Société Royale des Sciences de Liège, 2018

Narrow line Seyfert 1 (NLSy1) galaxies constitute a class of active galactic nuclei characterized by the full width at half maximum (FWHM) of the H broad emission line <2000 km s-1 and the flux ratio of [O III] to H <3. Their properties are not well understood since only a few NLSy1 galaxies were known earlier. We have studied various properties of NLSy1 galaxies using an enlarged sample and compared them with the conventional broad-line Seyfert 1 (BLSy1) galaxies. Both the sample of sources have z 0.8 and their optical spectra from SDSS-DR12 that are used to derive various physical parameters have a median signal to noise (S/N) ratio >10 pixel-1. A strong correlation between the H and Hα emission lines is found both in the FWHM and flux. The nuclear continuum luminosity is found to be strongly correlated with the luminosity of H, Hα and [O III] emission lines. The black hole mass in NLSy1 galaxies is lower compared to their broad line counterparts. Compared to BLSy1 g...

Optical Variability of Narrow‐Line Seyfert 1 Galaxies

The Astrophysical Journal, 2004

We report on a short optical monitoring programme of the narrow-line Seyfert 1 galaxy IRAS 13224À3809. Previous X-ray observations of this object have shown persistent giant variability. The degree of variability at other wavelengths may then be used to constrain the conditions and emission processes within the nucleus. Optical variability is expected if the electron population responsible for the soft X-ray emission is changing rapidly and Comptonupscattering infrared photons in the nucleus, or if the mechanism responsible for X-ray emission causes all the emission processes to vary together. We ®nd that there is no signi®cant optical variability, with a ®rm upper limit of 2 per cent, and conclude that the primary soft Xray emission region produces little of the observed optical emission. The X-ray and optical emission regions must be physically distinct and any reprocessing of X-rays into the optical waveband occurs some distance from the nucleus. The lack of optical variability indicates that the energy density of infrared radiation in the nucleus is at most equal to that of the ultraviolet radiation, because little is upscattered into the optical waveband. The extremely large X-ray variability of IRAS 13224À3809 may be explained by relativistic boosting of more modest variations. Although such boosting enhances X-ray variability over optical variability, this only partially explains the lack of optical variability.

Emission Line Properties of Seyfert Galaxies in the 12 μm Sample

The Astrophysical Journal

We present optical and ultraviolet spectroscopic measurements of the emission lines of 81 Seyfert 1 and 104 Seyfert 2 galaxies which comprise nearly all of the IRAS 12µm AGN sample. We have analyzed the emission-line luminosity functions, reddening, and other diagnostics. For example, the narrow-line regions (NLR) of Seyfert 1 and 2 galaxies do not significantly differ from each other in most of these diagnostics. Combining the Hα/Hβ ratio with a new reddening indicator-the [SII]6720/[OII]3727 ratio, we find the average E(B − V) is 0.49 ± 0.35 for Seyfert 1's and 0.52 ± 0.26 for Seyfert 2's. The NLR of Sy 1 galaxies has only insignificantly higher ionization level than in the Sy 2's. For the broad-line region (BLR), we find that the C IV equivalent width correlates more strongly with [O III]/Hβ than with UV luminosity. Our bright sample of local active galaxies includes 22 Seyfert nuclei with extremely weak broad wings in Hα, known as Seyfert 1.9's and 1.8's, depending on whether or not broad Hβ wings are detected. Aside from these weak broad lines, our low-luminosity Seyferts are more similar to the Sy2's than to the Sy 1's. In a a BPT diagram we find that Sy 1.8's and Sy 1.9's overlap the region occupied by the Sy 2 galaxies. We compare our results on optical emission lines with those obtained by previous investigators using AGN subsamples from the Sloan Digital Sky Survey. The luminosity functions of forbidden emission lines [OII]λ3727Å, [OIII]λ5007Å, and [SII]λ6720Å in Seyfert 1's and 2's are indistinguishable. They all show strong downward curvature. Unlike the LF's of Seyfert galaxies measured by the Sloan Digital Sky Survey, ours are nearly flat at low luminosities. The larger number of faint Sloan "AGN" is attributable to their inclusion of weakly emitting LINERs