| 1. |
- Abdo, A. A., et al.
(författare)
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A limit on the variation of the speed of light arising from quantum gravity effects
- 2009
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 462:7271, s. 331-334
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Tidskriftsartikel (refereegranskat)abstract
- A cornerstone of Einstein’s special relativity is Lorentz invariance—the postulate that all observers measure exactly the same speed of light in vacuum, independent of photon-energy. While special relativity assumes that there is no fundamental length-scale associated with such invariance, there is a fundamental scale (the Planck scale, lPlanck~1.62×10-33cm or EPlanck = MPlanckc2~1.22×1019GeV), at which quantum effects are expected to strongly affect the nature of space–time. There is great interest in the (not yet validated) idea that Lorentz invariance might break near the Planck scale. A key test of such violation of Lorentz invariance is a possible variation of photon speed with energy. Even a tiny variation in photon speed, when accumulated over cosmological light-travel times, may be revealed by observing sharp features in γ-ray burst (GRB) light-curves. Here we report the detection of emission up to ~31GeV from the distant and short GRB090510. We find no evidence for the violation of Lorentz invariance, and place a lower limit of 1.2EPlanck on the scale of a linear energy dependence (or an inverse wavelength dependence), subject to reasonable assumptions about the emission (equivalently we have an upper limit of lPlanck/1.2 on the length scale of the effect). Our results disfavour quantum-gravity theories in which the quantum nature of space–time on a very small scale linearly alters the speed of light.
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| 2. |
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| 3. |
- Miglio, A., et al.
(författare)
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PLATO as it is : A legacy mission for Galactic archaeology
- 2017
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : WILEY-V C H VERLAG GMBH. - 0004-6337 .- 1521-3994. ; 338:6, s. 644-661
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Tidskriftsartikel (refereegranskat)abstract
- Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but it will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental prerequisite to then reach the more ambitious goal of a similar level of accuracy, which will be possible only if we have at hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal that conveniently falls within the main aims of PLATO's core science. We therefore strongly endorse PLATO's current design and proposed observational strategy, and conclude that PLATO, as it is, will be a legacy mission for Galactic archaeology.
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| 4. |
- Abdo, A. A., et al.
(författare)
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Fermi Observations of High-energy Gamma-ray Emission from GRB 080825C
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 707:1, s. 580-592
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Tidskriftsartikel (refereegranskat)abstract
- The Fermi Gamma-ray Space Telescope has opened a new high-energy window in the study of gamma-ray bursts (GRBs). Here we present a thorough analysis of GRB 080825C, which triggered the Fermi Gamma-ray Burst Monitor (GBM), and was the first firm detection of a GRB by the Fermi Large Area Telescope (LAT). We discuss the LAT event selections, background estimation, significance calculations, and localization for Fermi GRBs in general and GRB 080825C in particular. We show the results of temporal and time-resolved spectral analysis of the GBM and LAT data. We also present some theoretical interpretation of GRB 080825C observations as well as some common features observed in other LAT GRBs.
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| 5. |
- Ackermann, M., et al.
(författare)
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DETECTION OF A SPECTRAL BREAK IN THE EXTRA HARD COMPONENT OF GRB 090926A
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 729:2, s. 114-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observation of the bright, long gamma-ray burst, GRB 090926A, by the Gamma-ray Burst Monitor and Large Area Telescope (LAT) instruments on board the Fermi Gamma-ray Space Telescope. GRB 090926A shares several features with other bright LAT bursts. In particular, it clearly shows a short spike in the light curve that is present in all detectors that see the burst, and this in turn suggests that there is a common region of emission across the entire Fermi energy range. In addition, while a separate high-energy power-law component has already been observed in other gamma-ray bursts, here we report for the first time the detection with good significance of a high-energy spectral break (or cutoff) in this power-law component around 1.4 GeV in the time-integrated spectrum. If the spectral break is caused by opacity to electron-positron pair production within the source, then this observation allows us to compute the bulk Lorentz factor for the outflow, rather than a lower limit.
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| 6. |
- Rauer, H., et al.
(författare)
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The PLATO 2.0 mission
- 2014
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 38:1-2, s. 249-330
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Tidskriftsartikel (refereegranskat)abstract
- PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s cadence) providing a wide field-of-view (2232 deg(2)) and a large photometric magnitude range (4-16 mag). It focuses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e. g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such a low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmospheres. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA's Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science.
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| 7. |
- Ackermann, M., et al.
(författare)
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Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A
- 2014
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 343:6166, s. 42-47
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Tidskriftsartikel (refereegranskat)abstract
- The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest gamma-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.
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| 8. |
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| 9. |
- Alonso, Jordi, et al.
(författare)
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The case for an international patient-reported outcomes measurement information system (PROMIS®) initiative.
- 2013
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Ingår i: Health and quality of life outcomes. - : Springer Science and Business Media LLC. - 1477-7525. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Patient-reported outcomes (PROs) play an increasingly important role in clinical practice and research. Modern psychometric methods such as item response theory (IRT) enable the creation of item banks that support fixed-length forms as well as computerized adaptive testing (CAT), often resulting in improved measurement precision and responsiveness. Here we describe and discuss the case for developing an international core set of PROs building from the US PROMIS® network.PROMIS is a U.S.-based cooperative group of research sites and centers of excellence convened to develop and standardize PRO measures across studies and settings. If extended to a global collaboration, PROMIS has the potential to transform PRO measurement by creating a shared, unifying terminology and metric for reporting of common symptoms and functional life domains. Extending a common set of standardized PRO measures to the international community offers great potential for improving patient-centered research, clinical trials reporting, population monitoring, and health care worldwide. Benefits of such standardization include the possibility of: international syntheses (such as meta-analyses) of research findings; international population monitoring and policy development; health services administrators and planners access to relevant information on the populations they serve; better assessment and monitoring of patients by providers; and improved shared decision making.The goal of the current PROMIS International initiative is to ensure that item banks are translated and culturally adapted for use in adults and children in as many countries as possible. The process includes 3 key steps: translation/cultural adaptation, calibration, and validation. A universal translation, an approach focusing on commonalities, rather than differences across versions developed in regions or countries speaking the same language, is proposed to ensure conceptual equivalence for all items. International item calibration using nationally representative samples of adults and children within countries is essential to demonstrate that all items possess expected strong measurement properties. Finally, it is important to demonstrate that the PROMIS measures are valid, reliable and responsive to change when used in an international context.IRT item banking will allow for tailoring within countries and facilitate growth and evolution of PROs through contributions from the international measurement community. A number of opportunities and challenges of international development of PROs item banks are discussed.
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| 10. |
- Chaplin-Kramer, R., et al.
(författare)
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Transformation for inclusive conservation : Evidence on values, decisions, and impacts in protected areas
- 2023
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Ingår i: Current Opinion in Environmental Sustainability. - : Elsevier. - 1877-3435 .- 1877-3443. ; 64
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Tidskriftsartikel (refereegranskat)abstract
- As countries consider new area-based conservation targets under the Convention on Biological Diversity, protected areas (PAs) and their impacts on people and nature are coming under increasing scrutiny. We review the evidence base on PA impacts, combining the findings from existing rigorous impact evaluations with local case studies developed for this study. We identify characteristics of PA establishment and management that improve the sustainability of biodiversity conservation and justice for local communities. We find that recognizing and respecting local values and knowledge about natural resource stewardship, colearning, and comanagement are key to achieving positive impacts for nature and people. Transforming PA governance toward more inclusive conservation depends upon the ability of PAs to be designed and implemented around the values and needs of local people.
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