363 research outputs found
X-ray absorption by Broad Line Region Clouds in Mrk 766
We present a new analysis of a 9-day long XMM-Newton monitoring of the Narrow
Line Seyfert 1 galaxy Mrk 766. We show that the strong changes in spectral
shape which occurred during this observation can be interpreted as due to Broad
Line Region clouds crossing the line of sight to the X-ray source. Within the
occultation scenario, the spectral and temporal analysis of the eclipses
provides precise estimates of the geometrical structure, location and physical
properties of the absorbing clouds. In particular, we show that these clouds
have cores with column densities of at least a few 10^23 cm^-2 and velocities
in the plane of the sky of the order of thousands km/s. The three different
eclipses monitored by XMM-Newton suggest a broad range in cloud velocities (by
a factor ~4-5). Moreover, two iron absorption lines clearly associated with
each eclipse suggest the presence of highly ionized gas around the obscuring
clouds, and an outflow component of the velocity spanning from 3,000 to 15,000
km/sComment: 10 pages, 7 figures. Accepted for publication in MNRA
Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides
This paper shows how to analyze plasmonic metal-insulator-metal waveguides
using the full modal structure of these guides. The analysis applies to all
frequencies, particularly including the near infrared and visible spectrum, and
to a wide range of sizes, including nanometallic structures. We use the
approach here specifically to analyze waveguide junctions. We show that the
full modal structure of the metal-insulator-metal (MIM) waveguides--which
consists of real and complex discrete eigenvalue spectra, as well as the
continuous spectrum--forms a complete basis set. We provide the derivation of
these modes using the techniques developed for Sturm-Liouville and generalized
eigenvalue equations. We demonstrate the need to include all parts of the
spectrum to have a complete set of basis vectors to describe scattering within
MIM waveguides with the mode-matching technique. We numerically compare the
mode-matching formulation with finite-difference frequency-domain analysis and
find very good agreement between the two for modal scattering at symmetric MIM
waveguide junctions. We touch upon the similarities between the underlying
mathematical structure of the MIM waveguide and the PT symmetric quantum
mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM
waveguide supports forms a canonical example against which other more
complicated geometries can be compared. Our work here encompasses the microwave
results, but extends also to waveguides with real metals even at infrared and
optical frequencies.Comment: 17 pages, 13 figures, 2 tables, references expanded, typos fixed,
figures slightly modifie
Dilemmas of Development and The Reconstruction of Fashion
Sustainable development by its nature appears elusive. It seems the more we try to capture and pin it down the more it moves away from us leading us into murkier waters and all manner of contradictions. No more is this felt than in the fashion industry where we are presented with a number of oppositions. The fashion cycle renders styles obsolete before they have worn out generating waste and over-consumptive practices. But it can also bring into the fore practices that have resonance to sustainable development in terms of their location, orientation and consideration for the environment. As studies emerge considering the detrimental environmental impacts of the manufacture and consumption of new clothes, second-hand clothes have become a focus for research endeavours considering how they can be reincorporated into the fashion system and have resonance to an ever ‘fashion’ hungry consumer. This chapter discusses methods for the processing of second-hand clothes into fashionable items and, by drawing on the wealth of ‘waste’ materials through reselling, restyling and remanufacturing, argues that ways of re-appropriating them into a more environmentally focused fashion industry is possible and necessary. It sets out as it hypothesis that the global fashion system has value in its transformative powers but that damaging and exploitative forces are still preventing it from being a force for good. This is due to the nature of the items being produced, the way they are manufactured and how they are ultimately consumed and disposed of
Supermassive Binaries and Extragalactic Jets
Some quasars show Doppler shifted broad emission line peaks. I give new
statistics of the occurrence of these peaks and show that, while the most
spectacular cases are in quasars with strong radio jets inclined to the line of
sight, they are also almost as common in radio-quiet quasars. Theories of the
origin of the peaks are reviewed and it is argued that the displaced peaks are
most likely produced by the supermassive binary model. The separations of the
peaks in the 3C 390.3-type objects are consistent with orientation-dependent
"unified models" of quasar activity. If the supermassive binary model is
correct, all members of "the jet set" (astrophysical objects showing jets)
could be binaries.Comment: 31 pages, PostScript, missing figure is in ApJ 464, L105 (see
http://www.aas.org/ApJ/v464n2/5736/5736.html
Intermediate and extreme mass-ratio inspirals — astrophysics, science applications and detection using LISA
Black hole binaries with extreme (gtrsim104:1) or intermediate (~102–104:1) mass ratios are among the most interesting gravitational wave sources that are expected to be detected by the proposed laser interferometer space antenna (LISA). These sources have the potential to tell us much about astrophysics, but are also of unique importance for testing aspects of the general theory of relativity in the strong field regime. Here we discuss these sources from the perspectives of astrophysics, data analysis and applications to testing general relativity, providing both a description of the current state of knowledge and an outline of some of the outstanding questions that still need to be addressed. This review grew out of discussions at a workshop in September 2006 hosted by the Albert Einstein Institute in Golm, Germany
X-ray Absorption and Reflection in Active Galactic Nuclei
X-ray spectroscopy offers an opportunity to study the complex mixture of
emitting and absorbing components in the circumnuclear regions of active
galactic nuclei, and to learn about the accretion process that fuels AGN and
the feedback of material to their host galaxies. We describe the spectral
signatures that may be studied and review the X-ray spectra and spectral
variability of active galaxies, concentrating on progress from recent Chandra,
XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for
absorption covering a wide range of column densities, ionization and dynamics,
and discuss the growing evidence for partial-covering absorption from data at
energies > 10 keV. Such absorption can also explain the observed X-ray spectral
curvature and variability in AGN at lower energies and is likely an important
factor in shaping the observed properties of this class of source.
Consideration of self-consistent models for local AGN indicates that X-ray
spectra likely comprise a combination of absorption and reflection effects from
material originating within a few light days of the black hole as well as on
larger scales. It is likely that AGN X-ray spectra may be strongly affected by
the presence of disk-wind outflows that are expected in systems with high
accretion rates, and we describe models that attempt to predict the effects of
radiative transfer through such winds, and discuss the prospects for new data
to test and address these ideas.Comment: Accepted for publication in the Astronomy and Astrophysics Review. 58
pages, 9 figures. V2 has fixed an error in footnote
A 0.8-2.4 microns spectral atlas of Active Galactic Nuclei
Aims: We present a near-infrared spectral atlas of 47 active galactic nuclei
(AGN), of all degrees of activity, in the wavelength interval of 0.8-2.4
microns, including the fluxes of the observed emission lines. We analyze the
spectroscopic properties of the continuum and emission line spectra of the
sources Methods: In order to exclude aperture and seeing effects we use
near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8-2.4
microns), taking the JHK-bands spectra simultaneously. Results: We present the
most extensive NIR spectral atlas of AGN to date. This atlas offers a suitable
database for studying the continuum and line emission properties of these
objects in a region full of interesting features. The shape of the continuum of
QSOs and Seyfert 1's are similar, being essentially flat in H and K band, in
the J band, a strong variation is found. In Seyfert 2 galaxies, the continuum
in the F_lambda X lambda space smoothly decreases from 1.2 microns redwards in
almost all sources. In J, it smoothly rises bluewards in some sources while in
others a small decreased in flux is observed. The spectra are dominated by
strong emission features of H I, He I, He II, [S III] and conspicuous forbidden
lines of low and high ionization species. Molecular lines of H2 are common
features to most objects. The absence of O I and Fe II lines in Seyfert 2
galaxies give observational support to the fact that these lines are formated
in the outermost portion of the broad line region. [P II] and coronal lines are
detected in all degrees of activity. The [Fe II] 12570A/16436A line ratio
becomes a reliable reddening indicator for the narrow-line region of Seyfert
galaxies.Comment: 39 pages, 17 figures, accepted for publication in Astronomy and
Astrophysics (15/05/2006
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black hole research,
as seen from a purely observational standpoint. Since the early '90s, rapid
technological advances, most notably the launch of the Hubble Space Telescope,
the commissioning of the VLBA and improvements in near-infrared speckle imaging
techniques, have not only given us incontrovertible proof of the existence of
supermassive black holes, but have unveiled fundamental connections between the
mass of the central singularity and the global properties of the host galaxy.
It is thanks to these observations that we are now, for the first time, in a
position to understand the origin, evolution and cosmic relevance of these
fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this
version contains low resolution figures. The full resolution version can be
downloaded from http://www.physics.rutgers.edu/~lff/publications.htm
IceCube-Gen2: A Vision for the Future of Neutrino Astronomy in Antarctica
The recent observation by the IceCube neutrino observatory of an
astrophysical flux of neutrinos represents the "first light" in the nascent
field of neutrino astronomy. The observed diffuse neutrino flux seems to
suggest a much larger level of hadronic activity in the non-thermal universe
than previously thought and suggests a rich discovery potential for a larger
neutrino observatory. This document presents a vision for an substantial
expansion of the current IceCube detector, IceCube-Gen2, including the aim of
instrumenting a volume of clear glacial ice at the South
Pole to deliver substantial increases in the astrophysical neutrino sample for
all flavors. A detector of this size would have a rich physics program with the
goal to resolve the sources of these astrophysical neutrinos, discover GZK
neutrinos, and be a leading observatory in future multi-messenger astronomy
programs.Comment: 20 pages, 12 figures. Address correspondence to: E. Blaufuss, F.
Halzen, C. Kopper (Changed to add one missing author, no other changes from
initial version.
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