3,040 research outputs found
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
A remarkable long-term light curve, and deep, low-state spectroscopy: Swift & XMM-Newton monitoring of the NLS1 galaxy Mkn 335
The Narrow-line Seyfert 1 galaxy (NLS1) Mkn 335 is remarkable because it has
repeatedly shown deep, long X-ray low-states which show pronounced spectral
structure. It has become one of the prototype AGN in deep minimum X-ray states.
Here we report on the continuation of our ongoing monitoring campaign with
Swift and the examination of the low state X-ray spectra based on a 200 ks
triggered observation with XMM in June 2009. Swift has continuously monitored
Mkn 335 since May 2007 typically on a monthly basis. This is one of the longest
simultaneous UV/X-ray light curves so far obtained for an active galactic
nucleus (AGN). Mkn 335 has shown strong X-ray variability even on time scales
of hours. In the UV, it turns out to be one of the most variable among NLS1s.
Long-term Swift monitoring allow us to examine correlations between the UV,
X-rays and X-ray hardness ratios. We find no significant correlation or lag
between the UV and X-ray variability; however, we do find distinct trends in
the behavior of the hardness ratio variability. The hardness ratio and count
rate are correlated in the low-flux state, but no correlation is seen in the
high-state. The X-ray low-state spectra of the 2007 and 2009 XMM observations
display significant spectral variability. We fit the X-ray spectra with a suite
of phenomenological models in order to characterize the data. The broad band
CCD spectrum can be fitted equally well with partial absorption and blurred
reflection models. These more complicated models are explored in further detail
in upcoming work.Comment: 23 pages, 8 figures, 4 Tables, ApJ Suppl. accepte
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 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
Field trials shows minor effect of modern plant breeding on grain yield of spring wheat at organic agriculture conditions
It cannot be generally recommended to use older varieties unless quality aspect are reflected in the price, but some old varieties were compatible with the commonly grown modern varieties. The results calls for targeted breeding for low input conditions, as breeding for high input condition contribute little to the benefit of organic agriculture and other low input conditions. Research is needed to quantify the effect of the different yield components of breeding on grain and straw yield and quality at low input conditions
Black Hole Growth & the M_BH--Bulge Relations
We present the black hole mass--bulge velocity dispersion relation for a
complete sample of 75 soft X-ray selected AGNs. We find that the AGNs with
highest accretion rates relative to Eddington lie below the \mbh--\sig\
relation of broad line Seyfert 1s, confirming the Mathur et al (2001) result.
The statistical result is robust and not due to any systematic measurement
error. This has important consequences towards our understanding of black hole
formation and growth: black holes grow by accretion in well formed bulges. As
they grow, they get closer to the \mbh--\sig relation for normal galaxies. The
accretion is highest in the beginning and dwindles as time goes by. Our result
does not support theories of the \mbh--\sig relation in which the black hole
mass is a constant fraction of the bulge mass/ velocity dispersion {\it at all
times} or those in which bulge growth is controlled by AGN feedback.Comment: To appear in "The Interplay among Black Holes, Stars and ISM in
Galactic Nuclei", IAU Symposium 222, Eds.: Th. Storchi Bergmann, L.C. Ho &
H.R. Schmit
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 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 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 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 ,
which provided new support for the pole-on orientation effect in NLS1s.Comment: 6 pages, 3 figures, accepted by MNRA
Statistical Properties of Narrow-Line Seyfert 1 galaxies
The number of publications considering Narrow-Line Seyfert 1 galaxies has
increased dramatically in recent years. Especially after the launch of the
X-ray missions ROSAT and ASCA, Narrow-Line Seyfert 1s have become very popular.
In these proceedings I will give an overview of how they are distributed over
the electromagnetic spectrum. I will describe what we know about them at radio,
infrared, optical, and X-ray bands, and how they differ and how they are
similar to Broad-Line Seyfert 1s. Finally I will introduce a method to find
them with high probability.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
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