Analysing the Suzaku Spectra of the Broad-Line Seyfert 1 Galaxy CBS 126

We analysed new simultaneous \emph{Suzaku} and \emph{Swift} data of the Broad Line Seyfert 1 (BLS1) galaxy CBS 126. A clear Fe emission line and a strong soft excess are present in the source spectra. We fit the spectra with a relativistic reflection model and find the model tends to fit the data with a high iron abundance possibly due to the large soft excess present. By checking the difference and the RMS spectra, we find there is likely an absorption edge at $\sim$ 0.89 keV, which might be caused by oxygen or neon. We also produced an analysis of the time-resolved spectra in order to examine the existence of the edge. Although high iron abundance is required more in the time-resolved spectra, a model of solar iron abundance together with an absorption edge gives a more physical explanation. Variation of the ionisation parameter is an alternative, plausible explanation for the excess seen in the difference spectra. It is difficult to know if there are warm absorbers in this source from the current data. To further investigate the presence of possible warm absorbers, higher signal-to-noise low-energy data are needed. The work presented here tentatively suggests that the spectra of a BLS1 can be explained by a relativistic reflection model similar to that often seen in their narrow-line cousins.Comment: 10 pages, 12 figures, accepted for publication in MNRA

Discovery of an Ultrasoft X-ray Transient Source in the 2XMM Catalog: a Tidal Disruption Event Candidate

We have discovered an ultrasoft X-ray transient source, 2XMMi J184725.1-631724, which was detected serendipitously in two XMM-Newton observations in the direction of the center of the galaxy IC 4765-f01-1504 at a redshift of 0.0353. These two observations were separated by 211 days, with the 0.2-10 keV absorbed flux increasing by a factor of about 9. Their spectra are best described by a model dominated by a thermal disk or a single-temperature blackbody component (contributing >80% of the flux) plus a weak power-law component. The thermal emission has a temperature of a few tens of eV, and the weak power-law component has a photon index of ~3.5. Similar to the black hole X-ray binaries in the thermal state, our source exhibits an accretion disk whose luminosity appears to follow the $L\propto T^4$ relation. This would indicate that the black hole mass is about 10^5-10^6 M_sun using the best-fitting inner disk radius. Both XMM-Newton observations show variability of about 21% on timescales of hours, which can be explained as due to fast variations in the mass accretion rate. The source was not detected by ROSAT in an observation in 1992, indicating a variability factor of >64 over longer timescales. The source was not detected again in X-rays in a Swift observation in 2011 February, implying a flux decrease by a factor of >12 since the last XMM-Newton observation. The transient nature, in addition to the extreme softness of the X-ray spectra and the inactivity of the galaxy implied by the lack of strong optical emission lines, makes it a candidate tidal disruption event. If this is the case, the first XMM-Newton observation would have been in the rising phase, and the second one in the decay phase.Comment: 12 pages, 6 figures. Accepted for publication in Ap

The Locus of Highly Accreting AGNs on the M_BH--sigma Plane: Selections, Limitations, and Implications

We re-examine the locus of narrow line Seyfert 1 galaxies on the M_BH--sigma (black hole mass--bulge velocity dispersion) plane in the light of the results from large new optically selected samples. We find that (1) soft X-ray selected NLS1s have a lower ratio of BH mass to \sigma^{4}_{[OIII]} than broad line Seyfert 1 galaxies; this remains a robust statistical result contrary to recent claims otherwise; (2) optically selected NLS1s have systematically lower Eddington luminosity ratio compared to X-ray selected NLS1s; and (3) as a result, the locus of NLS1s on the M_BH--sigma plane is affected by selection effects. We argue that there is no single explanation for the origin of the M_BH--sigma relation; instead tracks of galaxies on the M_BH--sigma plane differ with redshift, consistent with the downsizing of AGN activity. If these results at face value are incorrect, then the data imply that AGNs with high Eddington accretion reside preferentially in relatively late type galaxies at the present epoch, perhaps a more interesting result and a challenge to theoretical models.Comment: To appear in Ap

A Complete Sample of Soft X-ray Selected AGN: II. Statistical Analysis

Direct correlations and a Principal Component Analysis (PCA) are presented for a complete sample of 110 soft X-ray selected AGN of which about half are Narrow-Line Seyfert 1 galaxies (NLS1s). The direct correlation analyses show that narrower FWHM(H-beta) correlates with steeper X-ray spectrum, stronger optical FeII emission, weaker [OIII] emission and stronger short-term X-ray variability. This direct correlation analysis and the PCA confirm the Boroson & Green (1992) Eigenvector 1 relationship for AGN: FeII strength anti-correlates with [OIII] line strength. Eigenvector 1 is well-correlated with the Eddington luminosity ratio L/L_Edd while Eigenvector 2 shows a very good correlation with the mass of the central black hole and the mass accretion rate. The Eddington ratio L/L_Edd correlates with the X-ray spectral index alpha-X and the black home mass anti-correlates with the X-ray variability chi^2/nu. The Eddington ration L/L_Edd may be interpreted as the age of an AGN: AGN with steep X-ray spectra, strong FeII, and weak [OIII] are AGN in an early phase of their evolution. In this hypothesis NLS1s are young AGN.Comment: Accepted for publication in AJ (April 2004), 21 pages, 13 figure

Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I.Observational Results

We present optical spectra and emission-line ratios of 12 Narrow-Line Seyfert 1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A common feature in the EUV continuum of active galactic nuclei is the big blue bump (BBB), generally associated with thermal accretion disk emission. While Galactic absorption prevents direct access to the EUV range, it can be mapped by measuring the strength of a variety of forbidden optical emission lines that respond to different EUV continuum regions. We find that narrow emission-line ratios involving [OII]3727, Hbeta, [OIII]5007, [OI]6300, Halpha,[NII]6583, and [SII]6716,6731 indicate no significant difference between NLS1s and Broad-Line Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy distributions of their ionizing EUV - soft X-ray continua are similar. The relative strength of important forbidden high ionization lines like [NeV]3426 compared to HeII4686 and the relative strength of [FeX]6374 appear to show the same range as in BLS1 galaxies. However, a trend of weaker F([OI]6300)/F(Halpha) emission-line ratios is indicated for NLS1s compared to BLS1s. To recover the broad emission-line profiles we used Gaussian components. This approach indicates that the broad Hbeta profile can be well described with a broad component (FWHM = 3275 +- 800 km/s) and an intermediate broad component (FWHM = 1200 +- 300 km/s). The width of the broad component is in the typical range of normal BLS1s. The emission-line flux that is associated with the broad component in these NLS1s amounts to at least 60% of the total flux. Thus it dominates the total line flux, similar to BLS1 galaxies.Comment: 34 pages, 9 figures. accepted for publication in the Astrophys.Journa

SDSS J143030.22-001115.1: A misclassified narrow-line Seyfert 1 galaxy with flat X-ray spectrum

We used multi-component profiles to model H$\beta$ and [O III]$\lambda \lambda$4959,5007 lines for SDSS J143030.22-001115.1, a narrow-line Seyfert 1 galaxy (NLS1) in a sample of 150 NLS1s candidates selected from the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR). After subtracting the H$\beta$ contribution from narrow line regions (NLRs), we found that its full width half maximum (FWHM) of broad H$\beta$ line is nearly 2900 \kms, significantly larger than the customarily adopted criterion of 2000 \kms. With its weak Fe II multiples, we think that SDSS J143030.22-001115.1 can't be classified as a genuine NLS1. When we calculate the virial black hole masses of NLS1s, we should use the H$\beta$ linewidth after subtracting the H$\beta$ contribution from NLRs.Comment: 7 pages, 1 table, accepted by ChJA