From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 23-31 for Lyα, 27 for C IV λ1549, 19-24 for N V λ1240, 17-18 for Si IV λ1400, and 07-10 for He II λ1640. The most remarkable result, however, is the detection of apparent time delays between the different UV continuum bands. With respect to the UV continuum flux at 1315 A, the flux at 1485 A, 1740 A, and 1825 A lags with time delays of 021, 035, and 028, respectively. Determination of the significance of this detection is somewhat problematic since it depends on accurate estimation of the uncertainties in the lag measurements, which are difficult to assess. We attempt to estimate the uncertainties in the time delays through Monte Carlo simulations, and these yield estimates of ~007 for the 1 σ uncertainties in the interband continuum time delays. Possible explanations for the delays include the existence of a continuum-flux reprocessing region close to the central source and/or a contamination of the continuum flux with a very broad time-delayed emission feature such as the Balmer continuum or merged Fe II multiplets.

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei .11. Intensive monitoring of the ultraviolet spectrum of NGC 7469

Love Love Love

We present the results of a detailed multi-wavelength study of a sample of sixteen narrow-line Seyfert 1 (NLSy1) galaxies known in $\gamma$-rays so far. This includes a focused X-ray spectral analysis, to compare them with a more general NLSy1 population, and a broadband spectral energy distribution (SED) modeling considering the leptonic radiative processes to understand their similarity/dissimilarity with blazars. The X-ray spectra of $\gamma$-NLSy1 galaxies exhibit similarities both with typical NLSy1 sources below $\lesssim$2 keV and blazars at higher energies. We also find weak evidences of excess absorption in the soft X-ray spectra of 3 sources and a tentative detection of Fe line in 1H~0323+342. A comparison of the broadband parameters derived from the SED modeling reveals the similarity of $\gamma$-NLSy1 objects with blazars, in particular more with flat spectrum radio quasars. The $\gamma$-NLS1 galaxies host relatively low power jets with small bulk Lorentz factors with respect to blazars and this explains the paucity of such sources in the $\gamma$-ray catalogs and identification of an even fewer parent population members. Many of the observed features of these intriguing objects suggest they host low-mass black holes. The accretion rate in Eddington units can be considered as the driving factor to explain the physical properties of $\gamma$-NLSy1 sources, similar to that which is known for general blazar population.

General Physical Properties of Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies

We show that black holes grow substantially by accretion at close to Eddington rates. Using a complete sample of soft X-ray selected AGNs, 
Grupe & Mathur (2004) have shown that narrow line Seyfert 1 galaxies, as a class, lie below the M_BH-sigma relation of normal galaxies. Some NLS1s, however, lie on or close to the M_BH-sigma relation. Here we show that not all NLS1s accrete at close to Eddington rates: those with low {L/L_{Eddington}} are close to the M_BH-sigma relation, and those with high {L/L_{Eddington}} are far. With various tests in this paper, we argue that black holes grow in mass substantially in their high-accretion phase and approach the M_BH-sigma relation over time. The mass growth in a low accretion phase, as in BLS1s and also in some NLS1s, appears to be insignificant. Any theoretical model attempting to explain the M_BH-sigma relation will have to explain the above observations.

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Black hole growth by accretion

The soft X-ray excess - the excess of X-rays below 2 keV with respect to the extrapolation of the hard X-ray spectral continuum model - is a very common feature among type 1 active galactic nuclei (AGN); yet the nature of the soft X-ray excess is still poorly understood and hotly debated. To shed some light on this issue, we have measured in a model-independent way the soft excess strength in a flux-limited sample of broad-line and narrow-line Seyfert 1 galaxies (BLS1s and NLS1s) that are matched in X-ray luminosity but different in terms of the black hole mass and the accretion rate values, with NLS1s being characterized by smaller MBH and larger accretion rate values. Our analysis, in agreement with previous studies carried out with different AGN samples, indicates that: 1) a soft excess is ubiquitously detected in both BLS1s and NLS1s; 2) the strength of the soft excess is significantly larger in the NLS1 sample, compared to the BLS1 sample; 3) combining the two samples, the strength of the soft excess appears to positively correlate with the photon index as well as with the accretion rate, whereas there is no correlation with the black hole mass. Importantly, our work also reveals the lack of an anticorrelation between the soft excess strength and the luminosity of the primary X-ray component, predicted by the absorption and reflection scenarios. Our findings suggest that the soft excess is consistent with being produced by a warm Comptonization component. Larger, more complete samples of NLS1s and BLS1s are needed to confirm these conclusions.

The soft X-ray excess: NLS1s versus BLS1s

Are narrow-line Seyfert 1 galaxies highly accreting low-M BH AGNs?

In this work, we test the hypothesis that narrow-line Seyfert 1 galaxies (NSL1s) are active galactic nuclei in their early phase and are therefore younger and more active than the more common broad-line Seyfert 1 galaxies (BLS1s). If that is true, then NLS1s should, on average, have lower black hole (BH) masses and higher accretion rates than BLS1s. To test this, we use a sample of 35 NLS1s and 54 BLS1s with similar X-ray luminosity distributions and good XMM-Newton observations. To determine the BH mass MBH, we apply an X-ray scaling method that is independent of any assumptions on the broad-line region dynamics and the inclination of the objects. We find that, on average, NLS1s have lower BH masses, but the difference between the average MBH of NLS1s and BLS1s in our sample is only marginally significant (at the 2.6 sigma level). According to a Kolmogorov–Smirnov test, the distribution of MBH values of NLS1s is different from that of BLS1s at the 99% confidence level. Even stronger differences between NLS1s and BLS1s are inferred when the accretion rate distributions of NLS1s are compared to BLS1s, suggesting that the two populations are indeed distinct. Our study also indicates that the MBH values (both for NLS1s and BLS1s) determined with the X-ray scaling method are fully consistent with those obtained using reverberation mapping.

Ross V. Rudzinsky

Papers

Are narrow-line Seyfert 1 galaxies highly accreting low-M BH AGNs?

Are narrow-line Seyfert 1 galaxies highly accreting low M BH AGNs?