30 research outputs found
Discovery of a Radio Source following the 27 December 2004 Giant Flare from SGR 1806-20
Over a decade ago it was established that the remarkable high energy
transients, known as soft gamma-ray repeaters (SGRs), are a Galactic population
and originate from neutron stars with intense (<~ 10^15 G) magnetic fields
("magnetars"). On 27 December 2004 a giant flare (fluence >~ 0.3 erg/cm^2) was
detected from SGR 1806-20. Here we report the discovery of a fading radio
counterpart. We began a monitoring program from 0.2GHz to 250GHz and obtained a
high resolution 21-cm radio spectrum which traces the intervening interstellar
neutral Hydrogen clouds. Analysis of the spectrum yields the first direct
distance measurement of SGR 1806-20. The source is located at a distance
greater than 6.4 kpc and we argue that it is nearer than 9.8 kpc. If true, our
distance estimate lowers the total energy of the explosion and relaxes the
demands on theoretical models. The energetics and the rapid decay of the radio
source are not compatible with the afterglow model that is usually invoked for
gamma-ray bursts. Instead we suggest that the rapidly decaying radio emission
arises from the debris ejected during the explosion.Comment: 16 pages, 2 figures, submitted to Nature (substantial revisions
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
Clusters of galaxies : observational properties of the diffuse radio emission
Clusters of galaxies, as the largest virialized systems in the Universe, are
ideal laboratories to study the formation and evolution of cosmic
structures...(abridged)... Most of the detailed knowledge of galaxy clusters
has been obtained in recent years from the study of ICM through X-ray
Astronomy. At the same time, radio observations have proved that the ICM is
mixed with non-thermal components, i.e. highly relativistic particles and
large-scale magnetic fields, detected through their synchrotron emission. The
knowledge of the properties of these non-thermal ICM components has increased
significantly, owing to sensitive radio images and to the development of
theoretical models. Diffuse synchrotron radio emission in the central and
peripheral cluster regions has been found in many clusters. Moreover
large-scale magnetic fields appear to be present in all galaxy clusters, as
derived from Rotation Measure (RM) studies. Non-thermal components are linked
to the cluster X-ray properties, and to the cluster evolutionary stage, and are
crucial for a comprehensive physical description of the intracluster medium.
They play an important role in the cluster formation and evolution. We review
here the observational properties of diffuse non-thermal sources detected in
galaxy clusters: halos, relics and mini-halos. We discuss their classification
and properties. We report published results up to date and obtain and discuss
statistical properties. We present the properties of large-scale magnetic
fields in clusters and in even larger structures: filaments connecting galaxy
clusters. We summarize the current models of the origin of these cluster
components, and outline the improvements that are expected in this area from
future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics
Review. 58 pages, 26 figure
Immunomodulatory strategies prevent the development of autoimmune emphysema
<p>Abstract</p> <p>Background</p> <p>The presence of anti-endothelial cell antibodies and pathogenic T cells may reflect an autoimmune component in the pathogenesis of emphysema. Whether immune modulatory strategies can protect against the development of emphysema is not known.</p> <p>Methods</p> <p>Sprague Dawley rats were immunized with human umbilical vein endothelial cells (HUVEC) to induce autoimmune emphysema and treated with intrathymic HUVEC-injection and pristane. Measurements of alveolar airspace enlargement, cytokine levels, immuno histochemical, western blot analysis, and T cell repertoire of the lung tissue were performed.</p> <p>Results</p> <p>The immunomodulatory strategies protected lungs against cell death as demonstrated by reduced numbers of TUNEL and active caspase-3 positive cells and reduced levels of active caspase-3, when compared with lungs from HUVEC-immunized rats. Immunomodulatory strategies also suppressed anti-endothelial antibody production and preserved CNTF, IL-1alpha and VEGF levels. The immune deviation effects of the intrathymic HUVEC-injection were associated with an expansion of CD4+CD25+Foxp3+ regulatory T cells. Pristane treatment decreased the proportion of T cells expressing receptor beta-chain, Vβ16.1 in the lung tissue.</p> <p>Conclusions</p> <p>Our data demonstrate that interventions classically employed to induce central T cell tolerance (thymic inoculation of antigen) or to activate innate immune responses (pristane treatment) can prevent the development of autoimmune emphysema.</p
Photometry of the Hotspots of Cygnus A
We have observed the hotspots of Cygnus A with the JCMT1 at 1100 and 800μm. We find that the spectra of both hotspots are power laws from ~ 1 GHz to ~ 370 GHz