T. G. Wang

A population of radio-loud narrow-line Seyfert 1 galaxies with blazar-like properties?

Blazars having strong emission lines were found to be associated mostly with broad-line type 1 active galactic nuclei (AGNs). Hitherto, evidence for blazars identified with narrow-line Seyfert 1 (NLS1) AGNs was limited to only a very few individual cases. Here we present a comprehensive study of a sample of 23 genuine radio-loud NLS1 AGNs with radio loudness larger than 100. The radio sources of the sample are ubiquitously compact, unresolved on scales of several arcseconds. Some of these objects show interesting radio to X-ray properties that are unusual to most of the previously known radio-loud NLS1 AGNs, but are reminiscent of blazars. These include flat radio spectra, large-amplitude flux and spectral variability, compact VLBI cores, very high variability brightness temperatures, enhanced optical continuum emission, flat X-ray spectra, and blazar-like spectral energy distributions (SEDs). We interpret them as signatures of the postulated blazar nature of some of the objects, which likely possess at least moderately relativistic jets. Intrinsically, some of them have relatively low radio power and would have been classified as radio-intermediate AGNs. The black hole masses are estimated to be within 10(6)-10(8) M-circle dot, and the Eddington ratios close to unity, as in normal NLS1 AGNs. The results imply that radio-loud AGNs may be powered by black holes of moderate masses (similar to 10(6)-10(7) M-circle dot) accreting at high rates. Some of the objects, despite having strong emission lines, resemble high-energy-peaked BL Lac objects (HBLs) in their SEDs. Given the peculiarities of blazar-like NLS1 AGNs, questions arise as to whether they are plain downsizing extensions of normal radio-loud AGNs, or form a previously unrecognized population.

X-RAY PROPERTIES OF NARROW-LINE SEYFERT 1 GALAXIES WITH VERY SMALL BROADLINE WIDTHS

Narrow-line Seyfert 1 galaxies (NLS1s) with very small broadline widths (say, FWHM(H beta) less than or similar to 1200 km s(-1)) represent the extreme type of Seyfert 1 galaxies that have small black hole masses (M-BH) and/or high Eddington ratios (L/L-Edd). Here, we study the X-ray properties of a homogeneously and optically selected sample of 13 such objects, termed as very narrow line Seyfert 1 galaxies, using archival XMM-Newton data. It is found that the Fe K alpha emission line is at most weak in these objects. A soft X-ray excess is ubiquitous, with the thermal temperatures falling within a strict range of 0.1-0.2 keV. Our result highlights the puzzling independence of the thermal temperature by extending the relations to even smaller FWHM(H beta), i.e., smaller M-BH (similar to 10(6) M-circle dot) and/or higher L/L-Edd. The excess emission can be modeled by a range of viable models, though the disk reflection and Comptonization models generally give somewhat better fits over the smeared absorption and the p-free models. At the Eddington ratios around unity and above, the X-ray spectral slopes in the 2-10 keV band are systematically flatter than the predictions of the relationship with L/L-Edd suggested previously. Short timescale (1-2 hr) X-ray variability is common, which, together with the variability amplitude computed for some of the objects, is supportive of the scenario that NLS1s are indeed active galactic nuclei with relatively small M-BH.

On the X-Ray Baldwin Effect for Narrow Fe Kα Emission Lines

Most active galactic nuclei (AGNs) exhibit a narrow Fe Kα line at ~6.4 keV in the X-ray spectra, due to the fluorescent emission from cold material far from the inner accretion disk. Using XMM-Newton observations, Page et al. found that the equivalent width (EW) of the narrow Fe Kα line decreases with increasing luminosity (EW ∝ L-0.17±0.08), suggesting a decrease in the covering factor of the material emitting the line (presumably the torus). By combining the archival Chandra HETG observations of 34 type 1 AGNs with XMM observations in the literature, we build a much larger sample with 101 AGNs. We find a similar X-ray Baldwin effect in the sample (EW ∝ L-0.2015±0.0426); however, we note that the anticorrelation is dominated by the radio-loud AGNs in the sample, whose X-ray spectra might be contaminated by the relativistic jet. Excluding the radio-loud AGNs, we find a much weaker anticorrelation (EW ∝ L-0.1019±0.0524). We present Monte Carlo simulations showing that such a weak anticorrelation can be attributed to the relative short timescale variations of the X-ray continuum.

DEPENDENCE OF THE OPTICAL/ULTRAVIOLET VARIABILITY ON THE EMISSION-LINE PROPERTIES AND EDDINGTON RATIO IN ACTIVE GALACTIC NUCLEI

The dependence of the long-term optical/UV variability on the spectral and fundamental physical parameters for radio-quiet active galactic nuclei (AGNs) is investigated. The multi-epoch-repeated photometric scanning data in the Stripe-82 region of the Sloan Digital Sky Survey (SDSS) are exploited for two comparative AGN samples (mostly quasars) selected therein: a broad-line Seyfert 1 (BLS1) type sample and a narrow-line Seyfert 1 (NLS1) type AGN sample within redshifts 0.3-0.8. Their spectral parameters are derived from the SDSS spectroscopic data. It is found that on rest-frame timescales of several years the NLS1-type AGNs show systematically smaller variability compared to the BLS1-type AGNs. In fact, the variability amplitude is found to correlate, though only moderately, with the eigenvector 1 parameters, i.e., the smaller the H beta linewidth, the weaker the [O III] and the stronger the Fe II emission, the smaller the variability amplitude. Moreover, an interesting inverse correlation is found between the variability and the Eddington ratio, which is perhaps more fundamental. The previously known dependence of the variability on luminosity is not significant, and the dependence on black hole mass-as claimed in recent papers and also present in our data-fades out when controlling for the Eddington ratio in the correlation analysis, though these may be partly due to the limited ranges of luminosity and black hole mass of our samples. Our result strongly supports that an accretion disk is likely to play a major role in producing the optical/UV variability.

Two extreme double-peaked line emitters in the sloan digital sky survey

Double-peaked Balmer lines have been observed in about 150 active galactic nuclei and were interpreted preferentially as emission from relativistic accretion disks. We report the discovery of extreme double-peaked lines in SDSS J0942+0900 and SDSS J1417+6141. The FWHM of the Hα line, 40,600 km s-1, in the first object is almost twice as large as the broadest previously known. By comparing the line profile with accretion disk models, we find that most of the line flux is emitted from a narrow annulus around 100rg in SDSS J0942+0900, and from a disk with radii between 100rg and 400rg in SDSS J1417+6141. This is the first time that an accretion disk at radii below 100rg has been directly probed through optical emission lines. A certain asymmetry in the disk is required for both objects. Another, much weaker, broad Hα component (Wλ ~ 20 A and FWHM ~ 4000 km s-1) is also detected in both objects. Both objects show weak radio emission and strong high-ionization narrow lines.

Properties of broad band continuum of Narrow Line Seyfert 1 galaxies

We have performed a statistical study of the properties of the broad band continuum of Narrow Line Seyfert 1 galaxies (NLS1s) by collecting ratio, infrared, optical and X-ray continuum data from various databases and compared the results with control samples of Broad Line Seyfert 1 galaxies (BLS1s). We find that the fraction (∼ 6%) of Radio Loud (RL) NLS1s is significantly less than that of BLS1s (∼ 13%), which is caused by the lack of radio-very-loud sources in the former. The rarity of RL NLS1s, especially radio-very-loud ones, is consistent with the scenario of small black hole and high accretion rate for NLS1s. Six new radio loud NLS1s are found and five RL NLS1 candidates are presented. In comparison with the BLS1s, the NLS1s tend to have stronger far infrared emission, cooler infrared colors and redder B K color, which suggests that NLS1s are hosted by dust-richer nuclei. The NLS1s also show steeper soft X-ray spectrum and large soft X-ray to optical flux ratio, while a significant fraction show flat soft X-ray spectra. At least two factors can account for this, absorption and spectral variability. We also perform a correlation analysis between various broad band data. It is found that most correlations identified for NLS1s are also valid for radio quiet BLS1s: (1) the optical colors are anti-correlated with X-ray spectral index; (2) higher optical, X-ray and NIR luminosity objects show bluer optical colors and red H K color; (3) higher luminosity objects show warmer IRAS color; (4) the radio loudness correlates with B K and X-ray to optical flux ratio. Radio loud objects behave somewhat differently in a few correlations.

A COMPARATIVE STUDY OF OPTICAL/ULTRAVIOLET VARIABILITY OF NARROW-LINE SEYFERT 1 AND BROAD-LINE SEYFERT 1 ACTIVE GALACTIC NUCLEI

The ensemble optical/ultraviolet (UV) variability of narrow-line Seyfert 1 (NLS1)-type active galactic nuclei (AGNs) is investigated, based on a sample selected from the Sloan Digital Sky Survey (SDSS) Stripe 82 region with multi-epoch photometric scanning data. As a comparison, a control sample of broad-line Seyfert 1 (BLS1)-type AGNs is also incorporated. To quantify properly the intrinsic variation amplitudes and their uncertainties, a novel method of parametric maximum likelihood is introduced that has, as we argued, certain virtues over previously used methods. The majority of NLS1-type AGNs exhibit significant variability on timescales from about 10 days to a few years with, however, smaller amplitudes on average compared to BLS1-type AGNs. About 20 NLS1-type AGNs that show relatively large variations are presented and may deserve future monitoring observations, for instance, reverberation mapping. The averaged structure functions of variability, constructed using the same maximum likelihood method, show remarkable similarity in shape for the two types of AGNs on timescales longer than about 10 days, which can be approximated by a power law or an exponential function. This, along with other similar properties, such as the wavelength-dependent variability, is indicative of a common dominant mechanism responsible for the long-term optical/UV variability of both NLS1- and BLS1-type AGNs. Toward the short timescales, however, there is tentative evidence that the structure function of NLS1-type AGNs continues to decline, whereas that of BLS1-type AGNs flattens with some residual variability on timescales of days. If this can be confirmed, it may suggest that an alternative mechanism, such as X-ray reprocessing, starts to dominate in BLS1-type AGNs, but not in NLS1-type AGNs, on such timescales.

On the Correlation between Radio Properties and Black Hole Mass of Quasars

The question whether the radio properties of quasars are related to the mass of the central black hole or the accretion rate is important for our un- derstanding of the formation of relativistic jets, but no consensus has been reached from statistical analyses. Using two large quasar samples, one radio-selected, one optical-selected, we re-examined these relations and find that previous dierences between radio- and optical- selected samples can be ascribed, at least partly, to the eect of the narrow line component. All previous claimed correlations are much

A Long Decay of X-Ray Flux and Spectral Evolution in the Supersoft Active Galactic Nucleus GSN 069

GSN 069 is an optically identified very low-mass AGN which shows supersoft X-ray emission. The source is known to exhibit huge X-ray outburst, with flux increased by more than a factor of ~240 compared to the quiescence state. We report its long-term evolution in the X-ray flux and spectral variations over a time-scale of ~decade, using both new and archival X-ray observations from the XMM and Swift. The new Swift observations detected the source in its lowest level of X-ray activity since outburst, a factor of ~4 lower in the 0.2-2 keV flux than that obtained with the XMM observations nearly 8 years ago. Combining with the historical X-ray measurements, we find that the X-ray flux is decreasing slowly. There seemed to be spectral softening associated with the drop of X-ray flux. In addition, we find evidence for the presence of a weak, variable hard X-ray component, in addition to the dominant thermal blackbody emission reported before. The long decay of X-ray flux and spectral evolution, as well as the supersoft X-ray spectra, suggest that the source could be a tidal disruption event, though a highly variable AGN cannot be fully ruled out. Further continued X-ray monitoring would be required to test the TDE interpretation, through better determining the flux evolution in the decay phase.