36 research outputs found
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
No cold dust within the supernova remnant Cassiopeia A
A large amount (about three solar masses) of cold (18 K) dust in the
prototypical type II supernova remnant Cassiopeia A was recently reported. It
was concluded that dust production in type II supernovae can explain how the
large quantities (10^8 solar masses) of dust observed in the most distant
quasars could have been produced within only 700 million years after the Big
Bang. Foreground clouds of interstellar material, however, complicate the
interpretation of the earlier submillimetre observations of Cas A. Here we
report far-infrared and molecular line observations that demonstrate that most
of the detected submillimetre emission originates from interstellar dust in a
molecular cloud complex located in the line of sight between the Earth and Cas
A, and is therefore not associated with the remnant. The argument that type II
supernovae produce copious amounts of dust is not supported by the case of Cas
A, which previously appeared to provide the best evidence for this possibility.Comment: 13 pages, 3 figure
Supernova remnants: the X-ray perspective
Supernova remnants are beautiful astronomical objects that are also of high
scientific interest, because they provide insights into supernova explosion
mechanisms, and because they are the likely sources of Galactic cosmic rays.
X-ray observations are an important means to study these objects.And in
particular the advances made in X-ray imaging spectroscopy over the last two
decades has greatly increased our knowledge about supernova remnants. It has
made it possible to map the products of fresh nucleosynthesis, and resulted in
the identification of regions near shock fronts that emit X-ray synchrotron
radiation.
In this text all the relevant aspects of X-ray emission from supernova
remnants are reviewed and put into the context of supernova explosion
properties and the physics and evolution of supernova remnants. The first half
of this review has a more tutorial style and discusses the basics of supernova
remnant physics and thermal and non-thermal X-ray emission. The second half
offers a review of the recent advances.The topics addressed there are core
collapse and thermonuclear supernova remnants, SN 1987A, mature supernova
remnants, mixed-morphology remnants, including a discussion of the recent
finding of overionization in some of them, and finally X-ray synchrotron
radiation and its consequences for particle acceleration and magnetic fields.Comment: Published in Astronomy and Astrophysics Reviews. This version has 2
column-layout. 78 pages, 42 figures. This replaced version has some minor
language edits and several references have been correcte
Multi-ancestry genome-wide association meta-analysis of Parkinson’s disease
\ua9 2023, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply. Although over 90 independent risk variants have been identified for Parkinson’s disease using genome-wide association studies, most studies have been performed in just one population at a time. Here we performed a large-scale multi-ancestry meta-analysis of Parkinson’s disease with 49,049 cases, 18,785 proxy cases and 2,458,063 controls including individuals of European, East Asian, Latin American and African ancestry. In a meta-analysis, we identified 78 independent genome-wide significant loci, including 12 potentially novel loci (MTF2, PIK3CA, ADD1, SYBU, IRS2, USP8, PIGL, FASN, MYLK2, USP25, EP300 and PPP6R2) and fine-mapped 6 putative causal variants at 6 known PD loci. By combining our results with publicly available eQTL data, we identified 25 putative risk genes in these novel loci whose expression is associated with PD risk. This work lays the groundwork for future efforts aimed at identifying PD loci in non-European populations
Neutral hydrogen compact absorption features in Cassiopeia A
Very Large Array (VLA) observations of the lambda 21 cm HI line towards Cassiopeia A (Gas A) have been performed. The velocity interval observed was from -38 to -362 (LSR) km s(-1), with a resolution of 2.6 km s(-1) and a beam size of 14.2'' x 11.4'' Opacity images show the presence of a number of small absorption HI features in the velocity interval -62 to -69 km s(-1) (LSR) which, on the basis of several arguments, are postulated to be physically associated with Cas A. These cold HI knots have sizes of <0.1pc and show spatial substructure. Their velocities lie well outside the range of the intervening HI in the Perseus spiral arm, i.e. 0 to -55 km s(-1). We demonstrate that the HI knots cannot be described as shocked interstellar cloudlets engulfed by the blast wave of the supernova remnant (SNR). Instead, we propose that these low velocity HI features are recombined wind driven clumps moving ahead of the supernova (SN) shock front. This hypothesis is supported by the ages derived for the knots, varying from 8 x 10(3) to 5 x 10(4) years, which implies that these features were originally accelerated during the Wolf-Rayet (WR) phase of the precursor star