arXiv subjects

W. Bian

Publications and source records attributed to W. Bian.

44 records · Page 3Linked to original sources

arXiv2005

The Relation between the Inclinations of Broad Line Regions and the Accretion Disk

According to the standard model, an active galactic nucleus (AGN) consists of an inner accretion disk with a jet around a central massive black hole, and a number of outer broad line regions (BLRs) and narrow line regions (NLRs). The geometrical relationship between the BLRs and the accretion disk is not well understood. Assuming the motion of the BLRs is virialized and its configuration is disk-like, we derived its inclination to the line of sight for a sample of AGNs from their bulge stellar velocity dispersion, their size of the BLRs and their H$β$ linewidth. Compared with the inclination of the accretion disk obtained from the X-ray Fe K$α$ emission lines, we found that there is no positive correlation between the two. Our results showed that BLRs are not coplanar with the accretion disk and that we should be cautious of using the BLRs inclination as the disk inclination. The non-coplanar geometry of the outer BLRs and the inner accretion disk provides clues to the origin of BLRs and the properties of the accretion disk. Our preferable interpretation is that BLRs arise out of the outer part of a warped accretion disk.

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arXiv2004

Black hole masses in narrow-line Seyfert 1 galaxies

The masses of central supermassive black holes in a soft X-ray selected sample of the narrow-line Seyfert 1 galaxies (NLS1s) are estimated by some different methods to test their theoretical models. Apart from the methods using the H$β$ linewidth and the [O III] linewidth, soft X-ray excess as a prominent character of NLS1s is used to estimate the black hole masses. The virial mass derived from the H$β$ linewidth assuming random orbits of broad-line reigns (BLRs) is consistent with that from the soft X-ray bump luminosity for NLS1s but with a larger scatter. The virial black hole masses showed that most of NLS1s are in the super-Eddington accretion state while most of broad-line Seyfert 1 galaxies (BLS1s) are not. We found that the black hole mass estimated from [O III] linewidth is not in agreement with above two methods. Using the Eddington limit relation for the super-Eddington accretion suggested by Wang (2004), we found that there are 16 NLS1s satisfied with this Eddington limit relation. The masses of these 16 NLS1s derived from X-ray luminosity are systematically larger than that from H$β$ linewidth assuming random BLRs orbits. If the mass derived from X-ray luminosity is true, the mean disk inclination to the line of sight in these 16 NLS1s is about $17^{\circ}$, which provided new support for the pole-on orientation effect in NLS1s.

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arXiv2004

The mass estimate in narrow-line Seyfert 1 galaxies

It is possible that narrow-line Seyfert 1 galaxies (NLS1s) are in the early stage of active galactic nuclei (AGNs) evolution. It is important to estimate the mass of supermassive black hole (SBH) in NLS1s. Here we considered the different kinds of methods to estimate the SBH masses in NLS1s. The virial mass from the H$β$ linewidth assuming random orbits of broad line regions (BLRs) is consistent with that from the statured soft X-ray luminosity, which showed that most of NLS1s are in the super-Eddington accretion state. The mass from the [O III] linewidth is systematically larger than that from above two methods. It is necessary to measure he bulge stellar dispersion and/or bulge luminosity in NLS1s.

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arXiv2003

Difference of $α$-disks between Seyfert 1 galaxies and Quasars

In a previous paper (Bian & Zhao 2002), it was suggested that contamination to the luminosity of galactic nucleus from the host galaxies play an important role in determining parameters of the standard $α$ disk for AGNs. Using the nuclear absolute B band magnitude instead of the total absolute B band magnitude, the central black hole masses, the accretion rates and the disk inclinations to the line of sight for 20 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars were recalculated. It was found that small value of $α$ is needed in the accretion disk for Seyfert 1 galaxies compared with PG quasars. The difference of $α$ maybe lead to the different properties between Seyfert 1 galaxies and Quasars. Furthermore, we found most of the objects in this sample are not accreting at super-Eddington rates when we adopted the nuclear optical luminosity in our calculation.

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arXiv2003

The black hole--bulge relation in AGNs

We used the widths of H$β$ and [OIII] emission lines to investigate the black hole--bulge relation in radio-loud AGNs, radio-quiet AGNs and NLS1s. The central black hole mass, $M_{bh}$, is estimated from the H$β$ line width and the optical luminosity, and the bulge velocity dispersion, $σ$, is directly from the width of [OIII] line. We found that the radio-quiet AGNs follow the established $M_{bh}-σ$ relationship in nearby inactive galaxies, while the radio-loud AGNs and NLS1s deviate from this relationship. There are two plausible interpretations for the deviation of radio-loud AGNs. One is that the size of broad line regions (BLRs) emitting H$β$ line is overestimated because of the overestimation of optical luminosity, the other is that the dynamics of BLRs and/or narrow line regions (NLRs) in radio-loud AGNs is different from that in radio-quiet AGNs. The deviation of NLS1s may be due to the small inclination of BLRs to the line of sight or the reliability of [OIII] line width as the indicator of stellar velocity dispersion because of its complex multiple components.

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arXiv2003

On X-ray variability in narrow line and broad line AGNs

We assembled a sample of broad line and narrow lines AGNs observed by ASCA, whose excess variances have been determined. The central black hole masses in this sample can be obtained from the reverberation mapping method and the width of H$β$ emission line. Using the black hole masses and the bolometric luminosity, the Eddington ratio can also be obtained. We confirmed the strong anti-correlation between X-ray variability and the central black mass founded by Lu & Yu. We further found that narrow line Seyfert 1 galaxies (NLS1s) also follow this relation with a larger scatter and there is only a weak correlation between the X-ray variability and the Eddington ratio, which suggest that rapid variability and narrow lines in NLS1s are mainly due to small central black holes in NLS1s, not the difference of circumnuclear gas around NLS1s. A strong correlation was found between the hard X-ray photon index and the Eddington ratio. If the suggestion of two distinct accretion classes, namely ADAF and thin disk accretion, in AGNs (Lu & Yu) is correct, the strong photon index-Eddington ration correlation showed that there exists a kind of two zone accretion disk, in which the outer zone is a thin disk, and the inner zone is an ADAF disk. Otherwise, the accretion process is the thin disk accretion and the ADAF accretion is not required.

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arXiv2003

Timescales of Soft X-Ray Variability and Physical Constraints in Agns

We present soft X-ray variability time-scales for 65 active galactic nuclei (AGNs) derived from ROSAT/PSPC pointing data. For these 65 objects with obvious exponential increasing or decreasing patterns in their light curves, we use the exponential time-scales and find they are more suitable for analyzing ROSAT light curve data. We also discuss some physical constraints on the central engine implied by our results. Assuming that this soft X-ray variability exponential time-scale is approximately equal to the thermal timescale of the standard accretion disk, we obtain the accretion rate, the size of soft x-ray radiation region and the compactness parameter for 37 AGNs, using their recently estimated central black hole masses. For 12 of these 37 AGNs, the radii of the gravitational instability in the standard thin accretion disks are obtained using central black hole masses and the calculated accretion rates. These are consistent with the results from the reverberation mapping method. These results provide supporting evidence that such gravitational instabilities contribute to the formation of the Broad Line Regions (BLRs) in AGNs.

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arXiv2002

Masses, Accretion Rates and Inclinations of AGNs

We assume that the gravitational instability of standard thin accretion disks leads to the Broad Line Regions (BLRs), the B band luminosity comes from standard thin disk and the motion of BLRs is virial. The central black hole masses, the accretion rates and the disk inclinations to the line of sight for 17 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars have been calculated. Our results are sensitive to $α$ parameter of the standard $α$ disk. With the same values of $α$ ($α=1$), calculated central black hole masses for 17 Seyfert 1 galaxies are consistent with that from Kaspi et al. (2000) while that for 17 PG quasars are larger than that from Kaspi et al. (2000) by almost 2 orders of magnitude. Inclinations of 17 Seyfert 1 galaxies are about 6 times larger than that of 17 PG quasars. These inclinations, with a mean value of $32^{o}$ for 17 Seyfert 1 galaxies that agrees well with the result obtained by fitting the iron $Kα$ lines of Seyfert 1 galaxies observed with ASCA (Nandra et al. 1997) and the result obtained by Wu & Han (2001), provide further support for the orientation-dependent unification scheme of active galactic nuclei. There is a relation between the FWHM of H$β$ and the inclination, namely the inclination is smaller in AGNs with smaller FWHM of H$β$. The effect of inclinations in narrow line Seyfert 1 galaxies (NLS1s) should be considered when one studies the physics of NLS1s. (abbreviated)

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