135 research outputs found
Investigating ionized disc models of the variable narrow-line Seyfert 1 PG 1404+226
We investigate the use of relativistically blurred photoionized disc models
on an XMM-Newton observation of the Narrow Line Seyfert 1 galaxy PG 1404+226.
The model is designed to reproduce the radiation from the inner accretion disc
around a Kerr black hole, and is more successful at fitting the spectrum than
models based on a thermal soft excess. The source varies strongly over the
course of the observation, and the disc model works over all observed flux
states. We conclude that it is a useful tool in the study of certain quasars.Comment: 6 pages, 3 figures. Accepted for publication in MNRA
Suzaku observations of Markarian 335: evidence for a distributed reflector
We report on a 151 ks net exposure Suzaku observation of the Narrow Line
Seyfert 1 galaxy Mrk 335. The 0.5-40 keV spectrum contains a broad Fe line, a
strong soft excess below about 2 keV and a Compton hump around 20-30 keV. We
find that a model consisting of a power law and two reflectors provides the
best fit to the time-averaged spectrum. In this model, an ionized, heavily
blurred, inner reflector produces most of the soft excess, while an almost
neutral outer reflector (outside ~40 r_g) produces most of the Fe line
emission. The spectral variability of the observation is characterised by
spectral hardening at very low count rates. In terms of our power-law +
two-reflector model it seems like this hardening is mainly caused by pivoting
of the power law. The rms spectrum of the entire observation has the curved
shape commonly observed in AGN, although the shape is significantly flatter
when an interval which does not contain any deep dip in the lightcurve is
considered. We also examine a previous 133 ks XMM-Newton observation of Mrk
335. We find that the XMM-Newton spectrum can be fitted with a similar
two-reflector model as the Suzaku data and we confirm that the rms spectrum of
the observation is flat. The flat rms spectra, as well as the high-energy data
from the Suzaku PIN detector, disfavour an absorption origin for the soft
excess in Mrk 335.Comment: 13 pages, 13 figures. Accepted for publication in MNRA
Discovery of the Narrow-Line Seyfert 1 galaxy Mkn 335 in an historical low X-ray flux state
We report the discovery of the Narrow-Line Seyfert 1 galaxy Mkn 335 in an
extremely low X-ray state. A comparison of Swift observations obtained in May
and June/July 2007 with all previous X-ray observations between 1971 to 2006
show the AGN to have diminished in flux by a factor of more than 30, the lowest
X-ray flux Mkn 335 has ever been observed in. The Swift observations show an
extremely hard X-ray spectrum at energies above 2 keV. Possible interpretations
include partial covering absorption or X-ray reflection from the disk. In this
letter we consider the partial covering interpretation. The Swift observations
can be well fit by a strong partial covering absorber with varying absorption
column density N_H= 1-4 x 10^{23} cm-2 and a covering fraction f_c=0.9 - 1.
When corrected for intrinsic absorption, the X-ray flux of Mkn 335 varies by
only factors of 4-6. In the UV Mkn 335 shows variability in the order of 0.2
mag. We discuss the similarity of Mkn 335 with the highly variable NLS1
WPVS007, and speculate about a possible link between NLS1 galaxies and
broad-absorption line quasars.Comment: ApJ Letter accepted; 8 pages, 2 figures; The new version has three
more sentences in the introduction and three references added to the
discussio
An investigation of the origin of soft X-ray excess emission from Narrow-line Seyfert 1 galaxies Akn564 and Mrk1044
We investigate the origin of the soft X-ray excess emission from narrow-line
Seyfert 1 galaxies Akn564 and Mrk1044 using XMM-Newton observations. We find
clear evidence for time delays between the soft and hard X-ray emission from
Akn564 based on a 100ks long observation. The variations in the 4-10keV band
lag behind that in the 0.2-0.5keV band by 1768+/-122s. The full band power
density spectrum (PDS) of Akn~564 has a break at ~1.2e-3Hz with power-law
indices of ~1 and ~3 below and above the break. The hard (3-10keV) band PDS is
stronger and flatter than that in the soft (0.2-0.5keV) band. Based on a short
observation of Mrk1044, we find no correlation between the 0.2-0.3keV and
5-10keV bands at zero lag. These observations imply that the soft excess is not
the reprocessed hard X-ray emission. The high resolution spectrum of Akn564
obtained with the RGS shows evidence for a highly ionized and another weakly
ionized warm absorber medium. The smeared wind and blurred ionized reflection
models do not describe the pn data adequately. The spectrum is consistent with
a complex model consisting of optically thick Comptonization in a cool plasma
for the soft excess and a steep power-law, modified by two warm absorber media
as inferred from the RGS data and the foreground Galactic absorption. The
smeared wind and optically thick Comptonization models both describe the
spectrum of Mrk1044 satisfactorily, but the ionized reflection model requires
extreme parameters. The data suggest two component corona -- a cool, optically
thick corona for the soft excess and a hot corona for the power-law component.
The existence of a break in the soft band PDS suggests a compact cool corona
that can either be an ionized surface of the inner disk or an inner optically
thick region coupled to a truncated disk.Comment: Accepted for publication in ApJ, 19 page
Laboratory tests to understand tephra sliding behaviour on roofs
Following explosive eruptions, loading from tephra fall deposits can lead to roof collapse. However, the load may be reduced significantly by tephra sliding on pitched roofs. We present small-scale laboratory tests to investigate tephra sliding behaviour on metal, fibre cement sheet and tile roofing. We tested 10â30 cm thicknesses for dry and wet deposits of pumice, scoria and basaltic ash. We found that tephra did not slide on roof pitchesââ€â15° for coarse-grained deposits and â€â12° for dry ash. Thin deposits of wet ash were stable at pitchesââ€â30°. In addition, tephra was mainly shed on pitchesââ„â32° for metal roofs and â„â35° for fibre cement and tiles. Using these results, we have produced an initial set of sliding coefficients for tephra for simply pitched roofs that can be used to help prioritise roofs for clearing during an eruption and assist in designing roofs to withstand tephra fall
2003--2005 INTEGRAL and XMM-Newton observations of 3C 273
The aim of this paper is to study the evolution of the broadband spectrum of
one of the brightest and nearest quasars 3C 273.
We analyze the data obtained during quasi-simultaneous INTEGRAL and XMM
monitoring of the blazar 3C 273 in 2003--2005 in the UV, X-ray and soft
gamma-ray bands and study the results in the context of the long-term evolution
of the source.
The 0.2-100 keV spectrum of the source is well fitted by a combination of a
soft cut-off power law and a hard power law. No improvement of the fit is
achieved if one replaces the soft cut-off power law by either a blackbody, or a
disk reflection model. During the observation period the source has reached the
historically softest state in the hard X-ray domain with a photon index
. Comparing our data with available archived X-ray data
from previous years, we find a secular evolution of the source toward softer
X-ray emission (the photon index has increased by
over the last thirty years). We argue that existing theoretical models have to
be significantly modified to account for the observed spectral evolution of the
source.Comment: 11 pages, accepted to A&
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