163 research outputs found
Discovery of a bright radio transient in M82: a new radio supernova?
In this Letter, we report the discovery of a new bright radio transient in
M82. Using the Very Large Array, we observed the nuclear region of M82 at
several epochs at 22 GHz and detected a new bright radio source in this
galaxy's central region. We find a flux density for this flaring source that is
~300 times larger than upper limits determined in previous observations. The
flare must have started between 2007 October 29 and 2008 March 24. Over the
last year, the flux density of this new source has decreased from ~100 mJy to
~11 mJy. The lightcurve (based on only three data points) can be fitted better
with an exponential decay than with a power law. Based on the current data we
cannot identify the nature of this transient source. However, a new radio
supernova seems to be the most natural explanation. With it's flux density of
more than 100 mJy, it is at least 1.5 times brighter than SN1993J in M81 at the
peak of its lightcurve at 22 GHz.Comment: accepted Astronomy & Astrophysics, 4 pages, 3 figures, final version
& corrected abstract, also available at
http://www.mpifr-bonn.mpg.de/staff/abrunthaler/pub.shtm
Crossover between aperiodic and homogeneous semi-infinite critical behaviors in multilayered two-dimensional Ising models
We investigate the surface critical behavior of two-dimensional multilayered
aperiodic Ising models in the extreme anisotropic limit. The system under
consideration is obtained by piling up two types of layers with respectively
and spin rows coupled via nearest neighbor interactions and
, where the succession of layers follows an aperiodic sequence. Far
away from the critical regime, the correlation length is smaller
than the first layer width and the system exhibits the usual behavior of an
ordinary surface transition. In the other limit, in the neighborhood of the
critical point, diverges and the fluctuations are sensitive to the
non-periodic structure of the system so that the critical behavior is governed
by a new fixed point. We determine the critical exponent associated to the
surface magnetization at the aperiodic critical point and show that the
expected crossover between the two regimes is well described by a scaling
function. From numerical calculations, the parallel correlation length
is then found to behave with an anisotropy exponent which
depends on the aperiodic modulation and the layer widths.Comment: LaTeX file, 9 pages, 8 eps figures, to appear in Phys. Rev.
Physical Condition of Molecular Gas at the Centre of NGC 1097
We have used the Xco conversion factor, Local Thermal Equilibrium and Large
Velocity Gradient approximation to parametrize the cold and warm phase of the
interstellar medium from five different low transitions of CO in the central
21"(kpc) of NGC 1097. We have applied a one-component model and derived a
typical kinetic temperature of ~33K, and its molecular Hydrogen density and a
CO column density. A two-component model results in 85% cold-to-total gas
fraction with a 90K warm counterpart. Furthermore, we "resolve" the spatially
unresolved single dish observations by selecting velocity channels that in an
interferometric velocity map correspond to specific regions. We have selected
five such regions and found that the physical properties in these regions are
comparable to those derived from the full line profile. This implies that the
central kpc of NGC 1097 is rather homogeneous in nature, and, although the
regions are not uniquely located within the ring, the star formation along the
ring is homogeneously distributed (in agreement with recent Herschel
observations). We have further revised the mass inflow rate onto the
Supermassive Black Hole in this prototype LINER/Sy1 galaxy and found that,
accounting for the total interstellar medium and applying a careful
contribution of the disc thickness and corresponding stability criterion,
increases the previous estimations by a factor 10. Finally we have calculated
the Xco for the centre of NGC 1097 using an independent estimation of the
surface density to the CO emission, and obtained Xco=(2.8+-0.5)x10^20 cm^-2(K
km s^-1)^-1 at radius 10.5" and Xco=(5.0+-0.5)x10^20 cm^-2(K km s^-1)^-1 at
7.5". With the approach and analysis described, we have demonstrated that
important physical properties can be derived to a resolution beyond the single
dish resolution element, however, caution is necessary for interpreting the
results.(Abriged)Comment: 10 pages, 6 figures, 4 tables, Accepted for publication in MNRA
Polarisation Observations of VY Canis Majoris Water Vapour 5{32}-4{41} 620.701 GHz Maser Emission with HIFI
CONTEXT: Water vapour maser emission from evolved oxygen-rich stars remains
poorly understood. Additional observations, including polarisation studies and
simultaneous observation of different maser transitions may ultimately lead to
greater insight. AIMS: We have aimed to elucidate the nature and structure of
the VY CMa water vapour masers in part by observationally testing a theoretical
prediction of the relative strengths of the 620.701 GHz and the 22.235 GHz
maser components of ortho water vapour. METHODS: In its high-resolution mode
(HRS) the Herschel Heterodyne Instrument for the Infrared (HIFI) offers a
frequency resolution of 0.125 MHz, corresponding to a line-of-sight velocity of
0.06 km/s, which we employed to obtain the strength and linear polarisation of
maser spikes in the spectrum of VY CMa at 620.701 GHz. Simultaneous ground
based observations of the 22.235 GHz maser with the Max-Planck-Institut f\"ur
Radioastronomie 100-meter telescope at Effelsberg, provided a ratio of 620.701
GHz to 22.235 GHz emission. RESULTS:We report the first astronomical detection
to date of water vapour maser emission at 620.701 GHz. In VY CMa both the
620.701 and the 22.235 GHz polarisation are weak. At 620.701 GHz the maser
peaks are superposed on what appears to be a broad emission component, jointly
ejected asymmetrically from the star. We observed the 620.701 GHz emission at
two epochs 21 days apart, both to measure the potential direction of linearly
polarised maser components and to obtain a measure of the longevity of these
components. Although we do not detect significant polarisation levels in the
core of the line, they rise up to approximately 6% in its wings
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
The Development of Cephalic Armor in The Tokay Gecko (Squamata: Gekkonidae: \u3cem\u3eGekko gecko\u3c/em\u3e)
Armored skin resulting from the presence of bony dermal structures, osteoderms, is an exceptional phenotype in gekkotans (geckos and flap-footed lizards) only known to occur in three genera: Geckolepis, Gekko, and Tarentola. The Tokay gecko (Gekko gecko LINNAEUS 1758) is among the best-studied geckos due to its large size and wide range of occurrence, and although cranial dermal bone development has previously been investigated, details of osteoderm development along a size gradient remain less well-known. Likewise, a comparative survey of additional species within the broader Gekko clade to determine the uniqueness of this trait has not yet been completed. Here, we studied a large sample of gekkotans (38 spp.), including 18 specimens of G. gecko, using X-rays and high-resolution computed tomography for visualizing and quantifying the dermal armor in situ. Results from this survey confirm the presence of osteoderms in a second species within this genus, Gekko reevesii GRAY 1831, which exhibits discordance in timing and pattern of osteoderm development when compared with its sister taxon, G. gecko. We discuss the developmental sequence of osteoderms in these two species and explore in detail the formation and functionality of these enigmatic dermal ossifications. Finally, we conducted a comparative analysis of endolymphatic sacs in a wide array of gekkotans to explore previous ideas regarding the role of osteoderms as calcium reservoirs. We found that G. gecko and other gecko species with osteoderms have highly enlarged endolymphatic sacs relative to their body size, when compared to species without osteoderms, which implies that these membranous structures might fulfill a major role of calcium storage even in species with osteoderms
The NA49 large acceptance hadron detector
The NA49 detector is a wide acceptance spectrometer for the study of hadron production in p+p, p+A, and A+A collisions at the CERN SPS. The main components are 4 large volume TPCs for tracking and particle identification via . TOF scintillator arrays complement particle identification. Calorimeters for transverse energy determination and triggering, a detector for centrality selection in p+A collisions, and beam definition detectors complete the set-up. A description of all detector components is given with emphasis on new technical realizations. Performance and operational experience are discussed in particular with respect to the high track density environment of central Pb+Pb collisions
Primitive Duplicate Hox Clusters in the European Eel's Genome
The enigmatic life cycle and elongated body of the European eel (Anguilla anguilla L., 1758) have long motivated scientific enquiry. Recently, eel research has gained in urgency, as the population has dwindled to the point of critical endangerment. We have assembled a draft genome in order to facilitate advances in all provinces of eel biology. Here, we use the genome to investigate the eel's complement of the Hox developmental transcription factors. We show that unlike any other teleost fish, the eel retains fully populated, duplicate Hox clusters, which originated at the teleost-specific genome duplication. Using mRNA-sequencing and in situ hybridizations, we demonstrate that all copies are expressed in early embryos. Theories of vertebrate evolution predict that the retention of functional, duplicate Hox genes can give rise to additional developmental complexity, which is not immediately apparent in the adult. However, the key morphological innovation elsewhere in the eel's life history coincides with the evolutionary origin of its Hox repertoire
Synthetic Biology: Mapping the Scientific Landscape
This article uses data from Thomson Reuters Web of Science to map and analyse the scientific landscape for synthetic biology. The article draws on recent advances in data visualisation and analytics with the aim of informing upcoming international policy debates on the governance of synthetic biology by the Subsidiary Body on Scientific, Technical and Technological Advice (SBSTTA) of the United Nations Convention on Biological Diversity. We use mapping techniques to identify how synthetic biology can best be understood and the range of institutions, researchers and funding agencies involved. Debates under the Convention are likely to focus on a possible moratorium on the field release of synthetic organisms, cells or genomes. Based on the empirical evidence we propose that guidance could be provided to funding agencies to respect the letter and spirit of the Convention on Biological Diversity in making research investments. Building on the recommendations of the United States Presidential Commission for the Study of Bioethical Issues we demonstrate that it is possible to promote independent and transparent monitoring of developments in synthetic biology using modern information tools. In particular, public and policy understanding and engagement with synthetic biology can be enhanced through the use of online interactive tools. As a step forward in this process we make existing data on the scientific literature on synthetic biology available in an online interactive workbook so that researchers, policy makers and civil society can explore the data and draw conclusions for themselves
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