Radio observations of supernova remnant G1.9+0.3 Luken, Kieran J; Filipović, Miroslav D; Maxted, Nigel I ...
Monthly notices of the Royal Astronomical Society,
02/2020, Letnik:
492, Številka:
2
Journal Article
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ABSTRACT
We present 1–10 GHz radio continuum flux density, spectral index, polarization, and rotation measure (RM) images of the youngest known Galactic supernova remnant (SNR) G1.9+0.3, using ...observations from the Australia Telescope Compact Array. We have conducted an expansion study spanning eight epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (0.78 ± 0.09) per cent yr−1 (or ∼8900 km s−1 at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimetre. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of −0.81 ± 0.02 (76 MHz–10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (∼−1). Towards the two so-called (east and west) ‘ears’ of G1.9+0.3, we find very different RM values of 400–600 and 100–200 rad m2, respectively. The fractional polarization of the radio continuum emission reaches (19 ± 2) per cent, consistent with other, slightly older, SNRs such as Cas A.
The potentially devastating impacts of climate change on biodiversity and food security, together with the growing world population, means taking action to conserve crop wild relative (CWR) diversity ...is no longer an option—it is an urgent priority. CWR are species closely related to crops, including their progenitors, which have potential to contribute traits for crop improvement. However, their utilisation is hampered by a lack of systematic conservation which in turn is due to a lack of clarity over their identity. We used gene pool and taxon group concepts to estimate CWR relatedness for 173 priority crops to create the Harlan and de Wet inventory of globally important CWR taxa. Further taxa more remotely related to crops were added if they have historically been found to have useful traits for crop improvement. The inventory contains 1667 taxa, divided between 37 families, 108 genera, 1392 species and 299 sub-specific taxa. The region with the highest number of priority CWR is western Asia with 262 taxa, followed by China with 222 and southeastern Europe with 181. Within the primary gene pool, 242 taxa were found to be under-represented in ex situ collections and the countries identified as the highest priority for further germplasm collection are China, Mexico and Brazil. The inventory database is web-enabled (http://www.cwrdiversity.org/checklist/) and can be used to facilitate in situ and ex situ conservation planning at global, regional and national levels.
We examine the new Galactic supernova remnant (SNR) candidate, G23.11+0.18, as seen by the Murchison Widefield Array radio telescope. We describe the morphology of the candidate and find a spectral ...index of −0.63 0.05 in the 70-170 MHz domain. Coincident TeV gamma-ray detection in High Energy Stereoscopic System (HESS) data supports the SNR nature of G23.11+0.18 and suggests that G23.11+0.18 is accelerating particles beyond TeV energies, thus making this object a promising new cosmic-ray hadron source candidate. The remnant cannot be seen in current optical, infrared and X-ray data sets. We do find, however, a dip in CO-traced molecular gas at a line-of-sight velocity of ∼85 km s−1, suggesting the existence of a G23.11+0.18 progenitor wind-blown bubble. Furthermore, the discovery of molecular gas clumps at a neighboring velocity toward HESS J1832−085 adheres to the notion that a hadronic gamma-ray production mechanism is plausible toward the north of the remnant. Based on these morphological arguments, we propose an interstellar medium association for G23.11+0.18 at a kinematic distance of 4.6 0.8 kpc.
We present a model for the radio evolution of supernova remnants (SNRs) obtained by using three-dimensional hydrodynamic simulations coupled with nonlinear kinetic theory of cosmic-ray (CR) ...acceleration in SNRs. We model the radio evolution of SNRs on a global level by performing simulations for a wide range of the relevant physical parameters, such as the ambient density, supernova (SN) explosion energy, acceleration efficiency, and magnetic field amplification (MFA) efficiency. We attribute the observed spread of radio surface brightnesses for corresponding SNR diameters to the spread of these parameters. In addition to our simulations of Type Ia SNRs, we also considered SNR radio evolution in denser, nonuniform circumstellar environments modified by the progenitor star wind. These simulations start with the mass of the ejecta substantially higher than in the case of a Type Ia SN and presumably lower shock speed. The magnetic field is understandably seen as very important for the radio evolution of SNRs. In terms of MFA, we include both resonant and nonresonant modes in our large-scale simulations by implementing models obtained from first-principles, particle-in-cell simulations and nonlinear magnetohydrodynamical simulations. We test the quality and reliability of our models on a sample consisting of Galactic and extragalactic SNRs. Our simulations give − D slopes between −4 and −6 for the full Sedov regime. Recent empirical slopes obtained for the Galactic samples are around −5, while those for the extragalactic samples are around −4.
Crop breeders are currently facing the need to continue increasing crop production to feed the growing human population, while mitigating the negative impacts of climate change on agriculture. ...Taxonomic and genetic diversity, which includes taxa, genes and alleles that offer novel sources of resistance to pests, disease and abiotic factors that affect crop quality and quantity, are a key tool for crop breeders to address these challenges. Lack of access to this diversity is currently limiting crop improvement. This paper focuses on how the breeder's requirement for greater diversity may be met despite the continue challenges of growing human population, and the impacts of climate change. It is argued that gene pool diversity is largely concentrated in crop wild relatives (CWR) and their more active conservation, especially focusing on
in situ
conservation applications, will enable the breeding challenges to be met. Further, that the science of
in situ
conservation is only now coming of age but is sufficiently advanced to facilitate the establishment of integrated national, regional, and global
in situ
CWR conservation networks. For humankind to substantially benefit from the additional adaptive diversity made available through these collaborative networks for CWR
in situ
conservation for the first time, breeders need to be provided with the critical resources necessary to address the negative impacts of climate changes on food production—therefore promoting greater global food security.
We conduct a multiwavelength morphological study of the Galactic supernova remnant (SNR) RX J0852.0-4622 (also known as Vela Jr., Vela Z, and G266.2−1.2). RX J0852.0-4622 is coincident with the edge ...of the larger Vela SNR causing confusion in the attribution of some filamentary structures to either RX J0852.0-4622 or its larger sibling. We find that the RX J0852.0-4622 radio-continuum emission can be characterized by a two-dimensional shell with a radius of 0 90 0 01 (or 11.8 0.6 pc at an assumed distance of 750 pc) centered at (l, b) = (133 08 0 01,−46 34 0 01) (or R.A. = 8h52m19 2, decl. = −46°20′24 0, J2000), consistent with X-ray and gamma-ray emission. Although O iii emission features are generally associated with the Vela SNR, one particular O iii emission feature, which we denote as "the Vela Claw," morphologically matches a molecular clump that is thought to have been stripped by the stellar progenitor of the RX J0852.0-4622 SNR. We argue that the Vela Claw feature is possibly associated with RX J0852.0-4622. Toward the northwestern edge of RX J0852.0-4622 , we find a flattening of the radio spectral index toward another molecular clump also thought to be associated with RX J0852.0-4622 . It is currently unclear whether this feature and the Vela Claw result from interactions between the RX J0852.0-4622 shock and interstellar medium gas.
Humans require resilient, rapidly renewable and sustainable supplies of food and many other plant-derived supplies. However, the combined effects of climate change and population growth compromise ...the provision of these supplies particularly in respect to global food security. Crop wild relatives (CWR) contain higher genetic diversity than crops and harbour traits that can improve crop resilience and yield through plant breeding. However, in common with most countries, CWR are poorly conserved in England. There is currently no provision for long-term CWR conservation in situ, and comprehensive ex situ collection and storage of CWR is also lacking. However, there is a commitment to achieve their conservation in England's Biodiversity Strategy and the UK has international commitments to do so as part of the Global Plant Conservation Strategy. Here, we identify a series of measures that could enhance the conservation of English CWR, thereby supporting the achievement of these national and international objectives. We provide an inventory of 148 priority English CWR, highlight hotspots of CWR diversity in sites including The Lizard Peninsula, the Dorset coast and Cambridgeshire and suggest appropriate sites for the establishment of a complementary network of genetic reserves. We also identify individual in situ and ex situ priorities for each English CWR. Based on these analyses, we make recommendations whose implementation could provide effective, long-term conservation of English CWR whilst facilitating their use in crop improvement.
Indonesia is a country rich in medicinal plant biodiversity. The conservation and sustainable use of such species in Indonesia are critical because of incipient population growth, changing land ...usage, forest clearance, and climate change in a country where most of the population depends on traditional medicines for their health care and wellbeing. Identifying the conservation gap is crucial for planning the genetic conservation of Indonesian priority medicinal plant species. These are native plants with limited distribution, wild harvested (often to destruction) and/or included on the IUCN Red List, CITES appendices, and national legislation. Ecogeographic data were collated from online database, herbarium specimens and living collections and then subjected to in situ and ex situ gap analysis. The results of this gap analysis support our recommendation that in situ active conservation reserves for priority plants be established in areas of Indonesia with the greatest diversity of species. Medicinal plant species with no occurrence points in Indonesia or less than five seed samples are needed to be surveyed further. Other recommendations for active in situ and ex situ conservation are provided in this article which will help to ensure conservation of medicinal plants in Indonesia.
Crop landraces (LR), the traditional varieties of crops that have been maintained for millennia by repeated cycles of planting, harvesting, and selection, are genetically diverse compared to more ...modern varieties and provide one of the key components for crop improvement due to the ease of trait transfer within the crop species. However, LR diversity is increasingly threatened with genetic erosion and extinction by replacement with improved cultivars, lack of incentives for farmers to maintain traditional agricultural systems, and rising threats from climate change. Their active conservation is necessary to maintain this critical resource. However, as there are hundreds of thousands of LR and millions of LR populations for crops globally, active conservation is complex and resource-intensive. To assist in implementation, it is useful to be able to prioritise LR for conservation action and an obvious means of prioritisation is based on relative threat assessment. There have been several attempts to propose LR threat assessment methods, but none thus far has been widely accepted or applied. The aim of this paper is to present a novel, practical, standardised, and objective methodology for LR threat assessment derived from the widely applied IUCN Red Listing for wild species, involving the collation of time series information for LR population range, LR population trend, market, and farmer characteristics and LR context information. The collated information is compared to a set of threat criteria and an appropriate threat category is assigned to the LR when a threshold level is reached. The proposed methodology can be applied at national, regional, or global levels and any crop group.
Biodiversity loss is a major global challenge and minimizing extinction rates is the goal of several multilateral environmental agreements. Policy decisions require comprehensive, spatially explicit ...information on species' distributions and threats. We present an analysis of the conservation status of 14,669 European terrestrial, freshwater and marine species (ca. 10% of the continental fauna and flora), including all vertebrates and selected groups of invertebrates and plants. Our results reveal that 19% of European species are threatened with extinction, with higher extinction risks for plants (27%) and invertebrates (24%) compared to vertebrates (18%). These numbers exceed recent IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services) assumptions of extinction risk. Changes in agricultural practices and associated habitat loss, overharvesting, pollution and development are major threats to biodiversity. Maintaining and restoring sustainable land and water use practices is crucial to minimize future biodiversity declines.
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