677 research outputs found
Slim Disk Model for Narrow-Line Seyfert 1 Galaxies
We argue that both the extreme soft X-ray excess and the large-amplitude
variability of Narrow-Line Seyfert 1 galaxies (NLS1s) can be explained in the
framework of the slim disk model. When the disk luminosity approaches the
Eddington luminosity, the disk becomes a slim disk, exhibiting a multi-color
blackbody spectrum with a maximum temperature, T(bb), of about 0.2 (M/1e5 solar
masses)e(-1/4) keV, and size of the X-ray emitting region, r(bb), of about R(S)
(the Schwarzschild radius). Furthermore, magnetic energy can be amplified up to
a level exceeding radiation energy emitted from the disk, causing substantial
variability in X-rays by consecutive magnetic flares.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
First detection of hard X-ray photons in the soft X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007: The X-ray photon distribution observed by Swift
We report on the first detection of hard X-ray photons (E>2.5 keV) in the
X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007 which was the AGN with
the softest X-ray spectrum during the ROSAT All-Sky Survey. The AGN is clearly
detected at a level of about 2 x 10^{-17} W m^{-2} in the observed 0.3-10.0 keV
band by Swift in a 50 ks observation in 2007 September. For the first time
since the ROSAT All-Sky Survey observation in 1990 it was possible to derive an
X-ray photon distribution by adding together all Swift observations that have
been performed so far (85.5 ks in total). This photon distribution is
consistent with an X-ray spectrum of an AGN with a partial covering absorber
with a column density in the order of ~ 1 x 10^{23} cm^{-2} and a covering
fraction of about 90%. A comparison with the 2002 Chandra data suggests that
WPVS 007 has become brighter by a factor of about 4. The Swift data also
suggest that the absorber which is causing the current low-state may have
started to disappear. This disappearance is indicated by a significant change
in the hardness ratio from a very soft X-ray state during the 2005 October to
2007 January observations to a rather hard X-ray state in the 2007 September
observations. In the UV, WPVS 007 seems to become fainter by up to 0.5 mag over
the last two years. The optical to X-ray spectral slope derived from the
spectral energy distribution is alpha-ox=2.5 which classifies WPVS 007 as an
X-ray weak AGN. After correcting for reddening and X-ray absorption, alpha-ox
becomes 1.9 and the luminosity in the Big-Blue-Bump is log LBBB=37.7 [W], which
translates into an Eddington ratio
L/LEdd ~ 1.0.Comment: Accepted for publication in the Astronomical Journal, scheduled for
December 2008, 8 pages, 3 figures, 3 table
X-ray Continuum Slope and X-ray Spectral Features in NLS1 Galaxies
The idea that some of the unusual features in the X-ray spectra of
Narrow-Line Seyfert 1 galaxies (NLS1s) are due to the steep X-ray continuum is
tested by comparing photoionization model calculations with various observed
properties of Seyfert 1 galaxies. A meaningful comparison must involve the
careful use of the right X-ray ionization parameter, designated here U(oxygen).
When this is done, it is found that the strength of the continuum absorption
features is insensitive to the exact slope of the 0.1-50 keV continuum. It is
also shown that the complex of iron L-shell lines near 1 keV can produce strong
absorption and emission features, depending on the gas distribution and line
widths. While this may explain some unusual X-ray features in AGN, the
predicted intensity of the features do not distinguish NLS1 from broader line
sources. Finally, acceleration of highly ionized gas, by X-ray radiation
pressure, is also not sensitive to the exact slope of the X-ray continuum.Comment: Invited talk presented at the Joint MPE,AIP,ESO workshop on NLS1s,
Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at
http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
CIV Emission and the Ultraviolet through X-ray Spectral Energy Distribution of Radio-Quiet Quasars
In the restframe UV, two of the parameters that best characterize the range
of emission-line properties in quasar broad emission-line regions are the
equivalent width and the blueshift of the CIV line relative to the quasar rest
frame. We explore the connection between these emission-line properties and the
UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ)
quasars. Our sample consists of a heterogeneous compilation of 406 quasars from
the Sloan Digital Sky Survey and Palomar-Green survey that have well-measured
CIV emission-line and X-ray properties (including 164 objects with measured
Gamma). We find that RQ quasars with both strong CIV emission and small CIV
blueshifts can be classified as "hard-spectrum" sources that are (relatively)
strong in the X-ray as compared to the UV. On the other hand, RQ quasars with
both weak CIV emission and large CIV blueshifts are instead "soft-spectrum"
sources that are (relatively) weak in the X-ray as compared to the UV. This
work helps to further bridge optical/soft X-ray "Eigenvector 1" relationships
to the UV and hard X-ray. Based on these findings, we argue that future work
should consider systematic errors in bolometric corrections (and thus accretion
rates) that are derived from a single mean SED. Detailed analysis of the CIV
emission line may allow for SED-dependent corrections to these quantities.Comment: AJ, in press; 39 pages, 11 figures, 3 table
Warm absorbers in Narrow-Line Seyfert 1 galaxies
Warm absorbers are an important new tool for investigating the conditions
within the central regions of active galaxies. They have been observed in ~50%
of the well-studied Seyfert galaxies and have also been detected in quite a
number of Narrow-line Seyfert 1 galaxies (NLSy1). Here, we present a study of
the X-ray properties of several NLSy1s with focus on their warm absorbers: (a)
An analysis of all ROSAT PSPC observations of NGC 4051 including new ones is
performed, which reveals variability by a factor ~30 in count rate and much
less variability in the warm absorber parameters. (b) The possibility of a
dusty warm absorber in IRAS 13349+2438 is explored on the basis of
photoionization models for dusty warm gas and explicit ROSAT spectral fits. (c)
The X-ray spectrum of the NLSy1 1E0117.2-2837 is analyzed. It can be
successfully described by a very steep powerlaw of photon index G_x = -4, or
alternatively by a warm-absorbed flat powerlaw. UV-EUV emission lines expected
to arise from the warm material are predicted. (d) The strong spectral
variability of RX J0134.3-4258 (from G_x = -4.4 in the ROSAT survey
observation, to ~ -2.2$ in our subsequent pointing) is examined in terms of
warm absorption.Comment: 6 pages incl. 2 figures (needs paspconf.sty), to appear in the proc.
of "High Energy Processes in Accreting Black Holes" (Sweden, June 29 -July 4,
1998), J. Poutanen & R. Svensson (eds
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