12,850 research outputs found
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
Double dynamical regime of confined water
The Van Hove self correlation function of water confined in a silica pore is
calculated from Molecular Dynamics trajectories upon supercooling. At long time
in the relaxation region we found that the behaviour of the real space
time dependent correlators can be decomposed in a very slow, almost frozen,
dynamics due to the bound water close to the substrate and a faster dynamics of
the free water which resides far from the confining surface. For free water we
confirm the evidences of an approach to a crossover mode coupling transition,
previously found in Q space. In the short time region we found that the two
dynamical regimes are overimposed and cannot be distinguished. This shows that
the interplay between the slower and the faster dynamics emerges in going from
early times to the relaxation region, where a layer analysis of the
dynamical properties can be performed.Comment: 6 pages with 9 figures. RevTeX. Accepted for pulbication in J. Phys.
Cond. Mat
X-ray Spectral and Variability Properties of Low-Mass AGN
We study the X-ray properties of a sample of 14 optically-selected low-mass
AGN whose masses lie within the range 1E5 -2E6 M(solar) with XMM-Newton. Only
six of these low-mass AGN have previously been studied with sufficient quality
X-ray data, thus, we more than double the number of low-mass AGN observed by
XMM-Newton with the addition of our sample. We analyze their X-ray spectral
properties and variability and compare the results to their more massive
counterparts. The presence of a soft X-ray excess is detectable in all five
objects which were not background dominated at 2-3 keV. Combined with previous
studies, this gives a total of 8 low-mass AGN with a soft excess. The low-mass
AGN exhibit rapid, short-term variability (hundreds to thousands of seconds) as
well as long-term variability (months to years). There is a well-known
anti-correlation between black hole mass and variability amplitude (normalized
excess variance). Comparing our sample of low-mass AGN with this relation we
find that all of our sample lie below an extrapolation of the linear relation.
Such a flattening of the relation at low masses (below about 1E6 M(solar)) is
expected if the variability in all AGN follows the same shape power spectrum
with a break frequency that is dependent on mass. Finally, we also found two
objects that show significant absorption in their X-ray spectrum, indicative of
type 2 objects, although they are classified as type 1 AGN based on optical
spectra.Comment: 12 pages, 5 figures, 7 tables, accepted for publication in MNRA
Field induced evolution of regular and random 2D domain structures and shape of isolated domains in LiNbO<sub>3</sub> and LiTaO<sub>3</sub>
The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO3 and lithium tantalate LiTaO3. The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging
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
Molecular Characterization and Tissue Culture Regeneration Ability of the USA \u3ci\u3eArachis Pintoi\u3c/i\u3e (Krap. and Greg.) Germplasm Collection
Arachis pintoi Krap. and Greg. is a herbaceous, perennial legume, exclusively native to Brazil. It is considered a multiple use legume, being grown for forage; ground cover in fruits orchards, forest, and low tillage systems; erosion control; and ornamental purposes. Although several cultivars have been released in different countries, little is known about the genetic diversity of the germplasm stored in world genebanks. Our objective was to characterize and evaluate the genetic diversity of the germplasm of 35 accessions of Arachis pintoi at molecular level using RAPD markers. Concurrently, two tissue culture protocols were evaluated for their organogenesis ability. Further, variation in band profile was analyzed by comparing “Parent Plants” and tissue culture regenerated plants
Liquid-liquid coexistence in the phase diagram of a fluid confined in fractal porous materials
Multicanonical ensemble sampling simulations have been performed to calculate
the phase diagram of a Lennard-Jones fluid embedded in a fractal random matrix
generated through diffusion limited cluster aggregation. The study of the
system at increasing size and constant porosity shows that the results are
independent from the matrix realization but not from the size effects. A
gas-liquid transition shifted with respect to bulk is found. On growing the
size of the system on the high density side of the gas-liquid coexistence curve
it appears a second coexistence region between two liquid phases. These two
phases are characterized by a different behaviour of the local density inside
the interconnected porous structure at the same temperature and chemical
potential.Comment: 5 pages, 4 figures. To be published in Europhys. Letter
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