| 1. |
- Acero, F., et al.
(författare)
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Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7-3946
- 2017
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 840:2
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Tidskriftsartikel (refereegranskat)abstract
- We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7-3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti) correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H I emission. We present a series of simulated images of RX J1713.7-3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H I observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.
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| 2. |
- Abdalla, H., et al.
(författare)
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Gamma-ray blazar spectra with HESS II mono analysis : The case of PKS2155-304 and PG1553+113
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 600
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Tidskriftsartikel (refereegranskat)abstract
- Context. The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity to lower energies. The lowest energy threshold is obtained using monoscopic analysis of data taken with CT5, providing access to gamma-ray energies below 100 GeV for small zenith angle observations. Such an extension of the instrument's energy range is particularly beneficial for studies of active galactic nuclei with soft spectra, as expected for those at a redshift >= 0.5. The high-frequency peaked BL Lac objects PKS 2155-304 (z = 0.116) and PG 1553 + 113 (0.43 < z < 0.58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E > 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL). Aims. The aims of this work are twofold: to demonstrate the monoscopic analysis of CT5 data with a low energy threshold, and to obtain accurate measurements of the spectral energy distributions (SED) of PKS 2155-304 and PG 1553 + 113 near their SED peaks at energies approximate to 100 GeV. Methods. Multiple observational campaigns of PKS 2155 304 and PG 1553 + 113 were conducted during 2013 and 2014 using the full H.E.S.S. II instrument (CT1-5). A monoscopic analysis of the data taken with the new CT5 telescope was developed along with an investigation into the systematic uncertainties on the spectral parameters which are derived from this analysis. Results. Using the data from CT5, the energy spectra of PKS 2155 304 and PG 1553 + 113 were reconstructed down to conservative threshold energies of 80 GeV for PKS 2155 304, which transits near zenith, and 110 GeV for the more northern PG 1553 + 113. The measured spectra, well fitted in both cases by a log-parabola spectral model ( with a 5.0 similar to statistical preference for non-zero curvature for PKS 2155 304 and 4.5 sigma for PG 1553+113), were found consistent with spectra derived from contemporaneous Fermi-LAT data, indicating a sharp break in the observed spectra of both sources at E approximate to 100 GeV. When corrected for EBL absorption, the intrinsic H.E.S.S. II mono and Fermi-LAT spectrum of PKS 2155 304 was found to show significant curvature. For PG 1553+113, however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties.
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| 3. |
- de Castro Araujo Moreira, Andrea Cristina, et al.
(författare)
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The first Brazilian Field Lab fully dedicated to CO2 MMV experiments : from the start-up to the initial results
- 2014
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Ingår i: 12th International Conference on Greenhouse Gas Control Technologies, GHGT-12. - : Elsevier. ; , s. 6227-6238
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Konferensbidrag (refereegranskat)abstract
- Currently one of the main challenges in CO2 storage research is the development, testing and validation of accurate and efficient Measuring, Monitoring and Verification (MMV) techniques to be deployed at geological sequestration sites that are cost effective yet help minimize risk. This perspective motivated PETROBRAS, the National Oil Major in Brazil, through its R&D investments portfolio to prioritize research projects that would contribute to decreasing the technological gap in the area. The Company's periodic surveys indicated the lack of infrastructure, as well as expertise in CO2 MMV, as two of the most critical issues at the national level. In order to bridge that gap, initial steps were taken in 2010 for the start-up and development of the first CO2 MMV Field Lab in Brazil, fully sponsored by PETROBRAS, with a long term goal of enabling the ranking of the best, most cost-effective MMV technology alternatives to be deployed at commercial large scale CCGS sites scheduled to be installed in the country. In addition to providing basic infrastructure to carry out the CO2 injection and controlled release experiments, the facility was designed for the simultaneous testing of multiple measuring methodologies. Additional benefits of the initiative are the creation of expertise and the acceleration of the know-how in MMV in Brazil, as well as the development of a deeper and more practical knowledge of CO2 dynamics and impacts in a real world, open air scenario. Under the full support of the PETROBRAS R&D Center (CENPES), through its Climate Change Mitigation Technological Program (PROCLIMA), the Brazilian Pilot CO2 MMV Lab was made possible through a joint 4-year research Project, conceived and carried out by PETROBRAS and local academia in Brazil, in close cooperation with international experts. An overview of the Project and the multiple research areas encompassed will be presented, together with the preliminary results of the first CO2 injection campaign, which took place in 2013. (c) 2014 The Authors. Published by Elsevier
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| 4. |
- Franic, Iva, et al.
(författare)
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Climate, host and geography shape insect and fungal communities of trees
- 2023
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Non-native pests, climate change, and their interactions are likely to alter relationships between trees and tree-associated organisms with consequences for forest health. To understand and predict such changes, factors structuring tree-associated communities need to be determined. Here, we analysed the data consisting of records of insects and fungi collected from dormant twigs from 155 tree species at 51 botanical gardens or arboreta in 32 countries. Generalized dissimilarity models revealed similar relative importance of studied climatic, host-related and geographic factors on differences in tree-associated communities. Mean annual temperature, phylogenetic distance between hosts and geographic distance between locations were the major drivers of dissimilarities. The increasing importance of high temperatures on differences in studied communities indicate that climate change could affect tree-associated organisms directly and indirectly through host range shifts. Insect and fungal communities were more similar between closely related vs. distant hosts suggesting that host range shifts may facilitate the emergence of new pests. Moreover, dissimilarities among tree-associated communities increased with geographic distance indicating that human-mediated transport may serve as a pathway of the introductions of new pests. The results of this study highlight the need to limit the establishment of tree pests and increase the resilience of forest ecosystems to changes in climate.
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| 5. |
- Franic, Iva, et al.
(författare)
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Worldwide diversity of endophytic fungi and insects associated with dormant tree twigs
- 2022
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Ingår i: Scientific Data. - : Nature Publishing Group. - 2052-4463. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- International trade in plants and climate change are two of the main factors causing damaging tree pests (i.e. fungi and insects) to spread into new areas. To mitigate these risks, a large-scale assessment of tree-associated fungi and insects is needed. We present records of endophytic fungi and insects in twigs of 17 angiosperm and gymnosperm genera, from 51 locations in 32 countries worldwide. Endophytic fungi were characterized by high-throughput sequencing of 352 samples from 145 tree species in 28 countries. Insects were reared from 227 samples of 109 tree species in 18 countries and sorted into taxonomic orders and feeding guilds. Herbivorous insects were grouped into morphospecies and were identified using molecular and morphological approaches. This dataset reveals the diversity of tree-associated taxa, as it contains 12,721 fungal Amplicon Sequence Variants and 208 herbivorous insect morphospecies, sampled across broad geographic and climatic gradients and for many tree species. This dataset will facilitate applied and fundamental studies on the distribution of fungal endophytes and insects in trees.
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