333 research outputs found
Tracing a Disk Wind in NGC 3516
X-ray spectra of AGN often contain signatures indicative of absorption in
multiple layers of gas whose ionization-state and covering fraction may vary
with time. It has been unclear to date how much of the observed X-ray spectral
and timing behavior in AGN can be attributed to variations in absorption,
versus variations in the strengths of emission or reflection components.
Diagnostics of the inner regions of AGN cannot be reliably performed until the
origin of observed effects is understood. We investigate the role of the X-ray
absorbers in the Seyfert 1 galaxy NGC 3516. Time-averaged and flux-selected
spectroscopy is used to examine the behavior of NGC 3516 observed in Chandra
HETG and XMM data from Oct 2006. New H-like and He-like emission and absorption
features discovered in the Fe K regime reveal a previously unknown zone of
circumnuclear gas in NGC 3516 with log xi ~ 4.3 and column density 1E23 cm^-2.
A lower-ionization layer with log xi ~2 and of similar column density is
confirmed from previous observations, this layer has a covering fraction around
50%, and changes in covering provide a simple explanation of a deep dip in the
light curve that we interpret as an eclipse of the continuum due to passage of
a cloud across the sight line within half a day. These inner zones of absorbing
gas are detected to have outflow velocities in the range 1000-2000 km/s, this,
and constraints on radial location are consistent with an origin as part of a
disk wind in NGC 3516.Comment: 10 pages, 8 figures, accepted by A&A Feb 26 2008 Version 2: Figs 1 &
2 were corrected for a problem with ACIS section of the data. Little impact
on text of the pape
The High Energy view of the Broad Line Radio Galaxy 3C 111
We present the analysis of Suzaku and XMM-Newton observations of the
broad-line radio galaxy (BLRG) 3C 111. Its high energy emission shows
variability, a harder continuum with respect to the radio quiet AGN population,
and weak reflection features. Suzaku found the source in a minimum flux level;
a comparison with the XMM-Newton data implies an increase of a factor of 2.5 in
the 0.5-10 keV flux, in the 6 months separating the two observations. The iron
K complex is detected in both datasets, with rather low equivalent width(s).
The intensity of the iron K complex does not respond to the change in continuum
flux. An ultra-fast, high-ionization outflowing gas is clearly detected in the
XIS data; the absorber is most likely unstable. Indeed, during the XMM-Newton
observation, which was 6 months after, the absorber was not detected. No clear
roll-over in the hard X-ray emission is detected, probably due to the emergence
of the jet as a dominant component in the hard X-ray band, as suggested by the
detection above ~ 100 keV with the GSO on-board Suzaku, although the present
data do not allow us to firmly constrain the relative contribution of the
different components. The fluxes observed by the gamma-ray satellites CGRO and
Fermi would be compatible with the putative jet component if peaking at
energies E ~ 100 MeV. In the X-ray band, the jet contribution to the continuum
starts to be significant only above 10 keV. If the detection of the jet
component in 3C 111 is confirmed, then its relative importance in the X-ray
energy band could explain the different observed properties in the high-energy
emission of BLRGs, which are otherwise similar in their other multiwavelength
properties. Comparison between X-ray and gamma-ray data taken at different
epochs suggests that the strong variability observed for 3C 111 is probably
driven by a change in the primary continuum.Comment: Accepted for publication in MNRAS; 15 pages, 9 figures, 5 table
The High Magnetic Field Phase Diagram of a Quasi-One Dimensional Metal
We present a unique high magnetic field phase of the quasi-one dimensional
organic conductor (TMTSF)ClO. This phase, termed "Q-ClO", is
obtained by rapid thermal quenching to avoid ordering of the ClO anion. The
magnetic field dependent phase of Q-ClO is distinctly different from that
in the extensively studied annealed material. Q-ClO exhibits a spin density
wave (SDW) transition at 5 K which is strongly magnetic field
dependent. This dependence is well described by the theoretical treatment of
Bjelis and Maki. We show that Q-ClO provides a new B-T phase diagram in the
hierarchy of low-dimensional organic metals (one-dimensional towards
two-dimensional), and describe the temperature dependence of the of the quantum
oscillations observed in the SDW phase.Comment: 10 pages, 4 figures, preprin
X-ray Characteristics of NGC 3516: A View through the Complex Absorber
We consider new Suzaku data for NGC 3516 taken during 2009, along with other
recent X-ray observations of the source. The cumulative characteristics of NGC
3516 cannot be explained without invoking changes in the line-of-sight
absorption. Contrary to many other well-studied Seyfert galaxies, NGC 3516 does
not show a positive lag of hard X-ray photons relative to soft photons over the
timescales sampled. In the context of reverberation models for the X-ray lags,
the lack of such a signal in NGC 3516 is consistent with flux variations being
dominated by absorption changes. The lack of any reverberation signal in such a
highly variable source disfavors intrinsic continuum variability in this case.
Instead, the colorless flux variations observed at high flux states for NGC
3516 are suggested to be a consequence of Compton-thick clumps of gas crossing
the line-of-sight.Comment: 12 pages, 6 figures, accepted for publication in The Astrophysical
Journa
Nonequilibrium perturbation theory for complex scalar fields
Real-time perturbation theory is formulated for complex scalar fields away
from thermal equilibrium in such a way that dissipative effects arising from
the absorptive parts of loop diagrams are approximately resummed into the
unperturbed propagators. Low order calculations of physical quantities then
involve quasiparticle occupation numbers which evolve with the changing state
of the field system, in contrast to standard perturbation theory, where these
occupation numbers are frozen at their initial values. The evolution equation
of the occupation numbers can be cast approximately in the form of a Boltzmann
equation. Particular attention is given to the effects of a non-zero chemical
potential, and it is found that the thermal masses and decay widths of
quasiparticle modes are different for particles and antiparticles.Comment: 15 pages using RevTeX; 2 figures in 1 Postscript file; Submitted to
Phys. Rev.
Nonequilibrium perturbation theory for spin-1/2 fields
A partial resummation of perturbation theory is described for field theories
containing spin-1/2 particles in states that may be far from thermal
equilibrium. This allows the nonequilibrium state to be characterized in terms
of quasiparticles that approximate its true elementary excitations. In
particular, the quasiparticles have dispersion relations that differ from those
of free particles, finite thermal widths and occupation numbers which, in
contrast to those of standard perturbation theory evolve with the changing
nonequilibrium environment. A description of this kind is essential for
estimating the evolution of the system over extended periods of time. In
contrast to the corresponding description of scalar particles, the structure of
nonequilibrium fermion propagators exhibits features which have no counterpart
in the equilibrium theory.Comment: 16 pages; no figures; submitted to Phys. Rev.
An absorption origin for the X-ray spectral variability of MCG-6-30-15
The Seyfert I galaxy MCG-6-30-15 shows one of the best examples of a broad
"red wing" of emission in its X-ray spectrum at energies 2 < E < 6.4 keV,
commonly interpreted as being caused by relativistically-blurred reflection
close to the event horizon of the black hole. We aim to test an alternative
model in which absorption creates the observed spectral shape, explains the
puzzling lack of variability of the red wing and reduces the high reflection
albedo, substantially greater than unity, that is otherwise inferred at
energies E > 20 keV. We compiled all the available long-exposure, high-quality
data for MCG-6-30-15: 522 ks of Chandra HETGS, 282 ks of XMM-Newton pn/RGS and
253 ks of Suzaku XIS/PIN data. This is the first analysis of this full dataset.
We investigated the spectral variability on timescales >20 ks using principal
components analysis and fitted spectral models to "flux state" and mean spectra
over the energy range 0.5-45 keV (depending on detector). The absorber model
was based on the zones previously identified in the high-resolution grating
data. Joint fits were carried out to any data that were simultaneous. Multiple
absorbing zones covering a wide range of ionisation are required by the grating
data, including a highly ionised outflowing zone. A variable partial-covering
zone plus absorbed low-ionisation reflection, distant from the source, provides
a complete description of the variable X-ray spectrum. A single model fits all
the data. We conclude that these zones are responsible for the red wing, its
apparent lack of variability, the absorption structure around the Fe K-alpha
line, the soft-band "excess" and the high flux seen in the hard X-ray band. A
relativistically-blurred Fe line is not required in this model. We suggest the
partial covering zone is a clumpy wind from the accretion disk.Comment: Accepted for publication in Astronomy and Astrophysics. Corrected
versio
Formulating 'principles of procedure' for the foreign language classroom: A framework for process model language curricula
This article aims to apply Stenhouse's process model of curriculum to foreign language (FL) education, a model which is characterized by enacting principles of procedure which are specific to the discipline which the school subject belongs to. Rather than to replace or dissolve current approaches to FL teaching and curriculum development, this article seeks to improve and enrich communicative and task-based orientations with an additional criterion for assessing the educational worth of the tasks through which these orientations are developed. Unlike the objectives and competences models, principles of procedure provide an intrinsic justification of school curriculum by enacting the epistemological structure of any given area of knowledge in the educational process. Accordingly, the article will first justify the need to come up with a process model of curriculum for FL education which is built around such principles; then, it will formulate a basic framework that reflects the logical structure, concepts and epistemological perspectives of the language studies, as a first step to allowing these to enter the FL classroom and orient the teaching conducted in it; finally, it will present three tasks whose design was inspired by the abovementioned framework, and which were put into practice with Primary education English as a Foreign Language learners during the 2013 2014 and 2014 2015 academic years
Detection of the BL Lac Object H1426+428 at TeV Gamma Ray Energies
A very high energy (VHE) gamma-ray signal has been detected at the 5.4 sigma
level from H1426+428, an x-ray selected BL Lacertae object at a redshift of
0.129. The object was monitored from 1995 - 1998 with the Whipple 10m imaging
atmospheric Cherenkov telescope as part of a general blazar survey; the results
of these observations, although not statistically significant, were
consistently positive. X-ray observations of H1426+428 during 1999 with the
BeppoSAX instrument revealed that the peak of its synchrotron spectrum occurs
at > 100 keV, leading to the prediction of observable TeV emission from this
object. H1426+428 was monitored extensively at the Whipple Observatory during
the 1999, 2000, and 2001 observing seasons. The strongest TeV signals were
detected in 2000 and 2001. During 2001, an integral flux of 2.04 +/- 0.35
x10e-11 cm-2 s-1 above 280 GeV was recorded from H1426+428. The detection of
H1426+428 supports the idea that, as also seen in Markarian 501 and
1ES2344+514, BL Lacertae objects with extremely high synchrotron peak
frequencies produce gamma rays in the TeV range.Comment: 35 pages, 7 figures, accepted by ApJ Two upper limits in Table 3
(upper limits for 1995 and 1997) are different from the ApJ versio
Developments in the negative-U modelling of the cuprate HTSC systems
The paper deals with the many stands that go into creating the unique and
complex nature of the HTSC cuprates above Tc as below. Like its predecessors it
treats charge, not spin or lattice, as prime mover, but thus taken in the
context of the chemical bonding relevant to these copper oxides. The crucial
shell filling, negative-U, double-loading fluctuations possible there require
accessing at high valent local environment as prevails within the mixed valent,
inhomogeneous two sub-system circumstance of the HTSC materials. Close
attention is paid to the recent results from Corson, Demsar, Li, Johnson,
Norman, Varma, Gyorffy and colleagues.Comment: 44 pages:200+ references. Submitted to J.Phys.:Condensed Matter, Sept
7 200
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