202 research outputs found
G51.04+0.07 and its environment: Identification of a new Galactic supernova remnant at low radio frequencies
We have identified a new supernova remnant (SNR), G51.04+0.07, using observations at 74 MHz from the Very Large Array Low-Frequency Sky Survey Redux (VLSSr). Earlier, higher frequency radio continuum, recombination line, and infrared data had correctly inferred the presence of nonthermal radio emission within a larger, complex environment including ionised nebulae and active star formation. However, our observations have allowed us to redefine at least one SNR as a relatively small source (7.05 × 30in size) located at the southern periphery of the originally defined SNR candidate G51.21+0.11. The integrated flux density of G51.04+0.07 at 74 MHz is 6.1 ± 0.8 Jy, while its radio continuum spectrum has a slope α = −0.52 ± 0.05 (Sν ∝ να), typical of a shell-type remnant. We also measured spatial variations in the spectral index between 74 and 1400 MHz across the source, ranging from a steeper spectrum (α = −0.50 ± 0.04) coincident with the brightest emission to a flatter component (α = −0.30 ± 0.07) in the surrounding fainter region. To probe the interstellar medium into which the redefined SNR is likely evolving, we have analysed the surrounding atomic and molecular gas using the 21 cm neutral hydrogen (HI) and 13CO(J = 1 − 0) emissions. We found that G51.04+0.07 is confined within an elongated HI cavity and that its radio emission is consistent with the remains of a stellar explosion that occurred ∼6300 yr ago at a distance of 7.7 ± 2.3 kpc. Kinematic data suggest that the newly discovered SNR lies in front of HII regions in the complex, consistent with the lack of a turnover in the low frequency continuum spectrum. The CO observations revealed molecular material that traces the central and northern parts of G51.04+0.07. The interaction between the cloud and the radio source is not conclusive and motivates further study. The relatively low flux density (∼1.5 Jy at 1400 MHz) of G51.04+0.07 is consistent with this and many similar SNRs lying hidden along complex lines of sight towards inner Galactic emission complexes. It would also not be surprising if the larger complex studied here hosted additional SNRs.Fil: Supán, Jorge Leonardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Castelletti, Gabriela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Peters, W. M.. Spece Sciences División. Naval Research Laboratory; Estados UnidosFil: Kassim, N. E.. Spece Sciences División. Naval Research Laboratory; Estados Unido
Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1
We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and
G352.7-0.1, to understand the causes of such morphology. The research was
carried out based on new and reprocessed archival VLA observations and
XMM-Newton archival data. The surrounding was investigated based on data
extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring
Survey and the HI Southern Galactic Plane Survey. The present study revealed
that the overall morphology of both SNRs is the result of the mass-loss history
of their respective progenitor stars. Kes79 would be the product of the
gravitational collapse of a massive O9 star evolving near a molecular cloud and
within the precursor's wind-driven bubble, while G352.7-0.1 would be the result
of interactions of the SNR with an asymmetric wind from the progenitor together
with projection effects. No radio point source or pulsar wind nebula was found
associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray
study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray
radiation completely fills in the interior of the remnant and originates in
heated ejecta. Characteristic parameters, like radio flux, radio spectral
index, age, distance, shock velocity, initial energy and luminosity, were
estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and
Astrophysic
The most complete and detailed X-ray view of the SNR Puppis A
With the purpose of producing the first detailed full view of Puppis A in
X-rays, we carried out new XMM-Newton observations covering the missing regions
in the southern half of the supernova remnant (SNR) and combined them with
existing XMM-Newton and Chandra data. The new images were produced in the
0.3-0.7, 0.7-1.0 and 1.0-8.0 energy bands. We investigated the SNR morphology
in detail, carried out a multi-wavelength analysis and estimated the flux
density and luminosity of the whole SNR. The complex structure observed across
the remnant confirms that Puppis A evolves in an inhomogeneous, probably knotty
interstellar medium. The southwestern corner includes filaments that perfectly
correlate with radio features suggested to be associated with shock/cloud
interaction. In the northern half of Puppis A the comparison with Spitzer
infrared images shows an excellent correspondence between X-rays and 24 and 70
microns emission features, while to the south there are some matched and other
unmatched features. X-ray flux densities of 12.6 X 10^-9, 6.2 X 10^-9, and 2.8
X 10^-9 erg cm^-2 s^-1 were derived for the 0.3-0.7, 0.7-1.0 and 1.0-8.0 keV
bands, respectively. At the assumed distance of 2.2 kpc, the total X-ray
luminosity between 0.3 and 8.0 keV is 1.2 X 10^37 erg s^-1. We also collected
and updated the broad-band data of Puppis A between radio and GeV gamma-ray
range, producing its spectral energy distribution. To provide constraints to
the high-energy emission models, we re-analyzed radio data, estimating the
energy content in accelerated particles to be Umin=4.8 X 10^49 erg and the
magnetic field strength B=26 muG.Comment: Article accepted to be published in the Astronomy and Astrophysics
Main Journa
Thermal radio absorption as a tracer of the interaction of SNRs with their environments
We present new images and continuum spectral analysis for 14 resolved Galactic supernova remnants (SNRs) selected from the 74 MHz Very Large Array Low-Frequency Sky Survey Redux (VLSSr). We combine new integrated measurements from the VLSSr with, when available, flux densities extracted from the Galactic and Extragalactic All-Sky Murchison Widefield Array Survey and measurements from the literature to generate improved integrated continuum spectra sampled from ~15 MHz to ~217 GHz. We present the VLSSr images. When possible we combine them with publicly available images at 1.4 GHz, to analyse the resolved morphology and spectral index distribution across each SNR. We interpret the results and look for evidence of thermal absorption caused by ionised gas either proximate to the SNR itself, or along its line of sight. Three of the SNRs, G4.5+6.8 (Kepler), G28.6-0.1, and G120.1+1.4 (Tycho), have integrated spectra which can be adequately fit with simple power laws. The resolved spectral index map for Tycho confirms internal absorption which was previously detected by the Low Frequency Array, but it is insufficient to affect the fit to the integrated spectrum. Two of the SNRs are pulsar wind nebulae, G21.5-0.9 and G130.7+3.1 (3C 58). For those we identify high-frequency spectral breaks at 38 and 12 GHz, respectively. For the integrated spectra of the remaining nine SNRs, a low frequency spectral turnover is necessary to adequately fit the data. In all cases we are able to explain the turnover by extrinsic thermal absorption. For G18.8+0.3 (Kes 67), G21.8-0.6 (Kes 69), G29.7-0.3 (Kes 75), and G41.1-0.3 (3C 397), we attribute the absorption to ionised gas along the line of sight, possibly from extended H II region envelopes. For G23.3-0.3 (W41) the absorption can be attributed to H※ II regions located in its immediate proximity. Thermal absorption from interactions at the ionised interface between SNR forward shocks and the surrounding medium were previously identified as responsible for the low frequency turnover in SNR G31.9+0.0 (3C 391); our integrated spectrum is consistent with the previous results. We present evidence for the same phenomenon in three additional SNRs G27.4+0.0 (Kes 73), G39.2-0.3 (3C 396), and G43.3-0.2 (W49B), and derive constraints on the physical properties of the interaction. This result indicates that interactions between SNRs and their environs should be readily detectable through thermal absorption by future low frequency observations of SNRs with improved sensitivity and resolution.Fil: Castelletti, Gabriela Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Supán, Jorge Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Peters, W. M.. Spece Sciences División. Naval Research Laboratory; Estados UnidosFil: Kassim, N. E.. Spece Sciences División. Naval Research Laboratory; Estados Unido
Automated detection and characterization of Antarctic basal units using radar sounding data: demonstration in Institute Ice Stream, West Antarctica
Basal units – visibly distinct englacial structures near the ice-bed interface – warrant investigation for a number of reasons. Many are of unknown composition and origin, characteristics that could provide substantial insight into subglacial processes and ice-sheet history. Their significance, moreover, is not limited to near-bed depths; these units appear to dramatically influence the flow of surrounding ice. In order to enable improved characterization of these features, we develop and apply an algorithm that allows for the automatic detection of basal units. We use a tunable layer-optimized SAR processor to distinguish these structures from the bed, isochronous englacial layers and the ice-sheet surface, presenting a conceptual framework for the use of radio-echo character in the identification of ice-sheet features. We also outline a method by which our processor could be used to place observational constraints on basal units’ configuration, composition and provenance
Lack of coupling of D-2 receptors to adenylate cyclase in GH-3 cells exposed to epidermal growth factor. Possible role of a differential expression of Gi protein subtypes.
Exposure of GH-3 cells to epidermal growth factor for 4 consecutive days induced the expression of both D-2(415) and D-2(444) dopamine-receptor isoforms. Epidermal growth factor also promoted a remarkable increase in the content of Gi3 protein, which is responsible for receptor-induced activation of potassium channels in GH-3 cells. D-2 receptors in this model apparently activate a specific transducing pathway, leading to opening of potassium channels and inhibition of prolactin release by cAMP-independent mechanisms. This is shown by: 1) the selective D-2 agonist quinpirole, while inactive on vasoactive intestinal peptide-induced prolactin release, strongly inhibited the hormone secretion induced by neurotensin; 2) quinpirole, up to 100 microM, did not inhibit cAMP production evoked by vasoactive intestinal peptide both in intact cells and in broken cell membrane preparations; and 3) quinpirole and other D-2 agonists strongly potentiated Rb+ efflux when measured in a nominally calcium-free reaction solution containing 100 mM potassium (voltage-dependent component), but did not modify Rb+ efflux if measured in a reaction solution containing 1 mM calcium and 5 mM potassium (calcium-activated, cAMP-dependent component)
Late gadolinium enhancement in Brugada syndrome: A marker for subtle underlying cardiomyopathy?
BACKGROUND: There is increasing evidence that the Brugada ECG pattern is a marker of subtle structural heart disease. OBJECTIVE: We characterised Brugada syndrome (BrS) patients using cardiovascular magnetic resonance (CMR) with late gadolinium enhancement (LGE). METHODS: BrS was diagnosed according to international guidelines. 26% BrS patients carried SCN5A mutations. CMR data from 78 BrS patients were compared with 78 healthy controls (44±15 vs 42±14 years; p=0.434 and 64% vs 64% male; p=1.000). RESULTS: Right ventricular (RV) ejection fraction was slightly lower (61±8% vs 64±5%; p=0.004) and RV end-systolic volume slightly greater (31±10mL/m(2) vs 28±6mL/m(2); p=0.038) in BrS compared with controls. These values remained within the normal range. LGE was demonstrated in 8% BrS patients (left ventricular (LV) midwall LGE in 5%) but not in controls (p=0.028). In BrS patients with midwall LGE there were no other features of cardiomyopathy at the time of CMR but genetic testing and follow-up has revealed a desmoplakin mutation in one patient and evolution of T-wave inversion throughout all precordial ECG leads in another. Neither patient fulfils diagnostic criteria for arrhythmogenic right ventricular cardiomyopathy. CONCLUSION: Some BrS patients have LV midwall LGE consistent with an underlying cardiomyopathic process. Even cases without LGE show greater RV volumes and reduced RV function. These findings lend further support to the presence of subtle structural abnormalities in BrS. The BrS pattern with LGE may serve as early markers for evolution of a cardiomyopathic phenotype over time. CMR is a potentially useful adjunct investigation in the clinical evaluation of BrS
Exploding the myths: An introduction to artificial neural networks for prediction and forecasting
Artificial Neural Networks (ANNs), sometimes also called models for deep learning, are used extensively for the prediction of a range of environmental variables. While the potential of ANNs is unquestioned, they are surrounded by an air of mystery and intrigue, leading to a lack of understanding of their inner workings. This has led to the perpetuation of a number of myths, resulting in the misconception that applying ANNs primarily involves "throwing" a large amount of data at "black-box" software packages. While this is a convenient way to side-step the principles applied to the development of other types of models, this comes at significant cost in terms of the usefulness of the resulting models. To address these issues, this inroductory overview paper explodes a number of the common myths surrounding the use of ANNs and outlines state-of-the-art approaches to developing ANNs that enable them to be applied with confidence in practice
MHD models of Pulsar Wind Nebulae
Pulsar Wind Nebulae (PWNe) are bubbles or relativistic plasma that form when
the pulsar wind is confined by the SNR or the ISM. Recent observations have
shown a richness of emission features that has driven a renewed interest in the
theoretical modeling of these objects. In recent years a MHD paradigm has been
developed, capable of reproducing almost all of the observed properties of
PWNe, shedding new light on many old issues. Given that PWNe are perhaps the
nearest systems where processes related to relativistic dynamics can be
investigated with high accuracy, a reliable model of their behavior is
paramount for a correct understanding of high energy astrophysics in general. I
will review the present status of MHD models: what are the key ingredients,
their successes, and open questions that still need further investigation.Comment: 18 pages, 5 figures, Invited Review, Proceedings of the "ICREA
Workshop on The High-Energy Emission from Pulsars and their Systems", Sant
Cugat, Spain, April 12-16, 201
The low frequency radio emission and spectrum of the extended SNR W44: new VLA observations at 74 and 324 MHz
We present new Very Large Array (VLA) radio images at 74 and 324 MHz of the
SNR W44. The VLA images, obtained with unprecedented angular resolution and
sensitivity for such low frequencies have been used in combination with
existing 1442 MHz radio data, Spitzer IR data, and ROSAT and Chandra X-ray data
to investigate morphological and spectral properties of this SNR. The spatially
resolved spectral index study revealed that the bright filaments, both around
and across the SNR, have a straight spectrum between 74 and 1442 MHz, with
alpha ~ -0.5, with two clear exceptions: a short portion of the SNR limb to the
southeast, with alpha varying between 0 and +0.4 and a bright arc to the west
where the spectrum breaks around 300 MHz and looks concave down. We conclude
that at the shell and along the internal filaments, the electrons responsible
for the synchrotron emission were accelerated at the shock according to a
simple diffusive shock model; the positive spectrum corresponds to a location
where the SN shock is running into a molecular cloud and where the line of
sight intersects the photo dissociation region of an HII region and a young
stellar object is present. The curved spectrum on the westernmost bright arc is
explained as the consequence of strong post-shock densities and enhanced
magnetic fields after the interaction of the SN shock with a collindant
molecular cloud.Comment: After language edited, 16 pages, 12 figures (3 in color). Figures
degraded to reduce file size. Accepted 01/03/2007 for publicaion in A&
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