| 1. |
- Acharya, B. S., et al.
(författare)
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Introducing the CTA concept
- 2013
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 43, s. 3-18
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Actis, M., et al.
(författare)
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Design concepts for the Cherenkov Telescope Array CTA : an advanced facility for ground-based high-energy gamma-ray astronomy
- 2011
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Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 32:3, s. 193-316
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Tidskriftsartikel (refereegranskat)abstract
- Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
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| 3. |
- 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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| 4. |
- Ackermann, M., et al.
(författare)
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Fermi observations of GRB 090510 : A short-hard gamma-ray burst with an additional, hard power-law component from 10 keV to GeV energies
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 716:2, s. 1178-1190
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Tidskriftsartikel (refereegranskat)abstract
- We present detailed observations of the bright short-hard gamma-ray burst GRB 090510 made with the Gammaray Burst Monitor (GBM) and Large Area Telescope (LAT) on board the Fermi observatory. GRB 090510 is the first burst detected by the LAT that shows strong evidence for a deviation from a Band spectral fitting function during the prompt emission phase. The time-integrated spectrum is fit by the sum of a Band function with E-peak = 3.9 +/- 0.3 MeV, which is the highest yet measured, and a hard power-law component with photon index -1.62 +/- 0.03 that dominates the emission below approximate to 20 keV and above approximate to 100 MeV. The onset of the high-energy spectral component appears to be delayed by similar to 0.1 s with respect to the onset of a component well fit with a single Band function. A faint GBM pulse and a LAT photon are detected 0.5 s before the main pulse. During the prompt phase, the LAT detected a photon with energy 30.5(-2.6)(+5.8) GeV, the highest ever measured from a short GRB. Observation of this photon sets a minimum bulk outflow Lorentz factor, Gamma greater than or similar to 1200, using simple.. opacity arguments for this GRB at redshift z = 0.903 and a variability timescale on the order of tens of ms for the approximate to 100 keV-few MeV flux. Stricter high confidence estimates imply Gamma greater than or similar to 1000 and still require that the outflows powering short GRBs are at least as highly relativistic as those of long-duration GRBs. Implications of the temporal behavior and power-law shape of the additional component on synchrotron/synchrotron self-Compton, external-shock synchrotron, and hadronic models are considered.
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| 6. |
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| 7. |
- Toma, M., et al.
(författare)
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The relationship between left ventricular ejection fraction and mortality in patients with acute heart failure: insights from the ASCEND-HF Trial
- 2014
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Ingår i: European Journal of Heart Failure. - : Wiley. - 1388-9842. ; 16:3, s. 334-41
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Tidskriftsartikel (refereegranskat)abstract
- AIM: Acute decompensated heart failure (ADHF) is associated with significant morbidity and mortality but the relationship between LVEF and outcomes is unclear. We explored the association between LVEF and 30 and 180 day mortality in 7007 ADHF patients enrolled in the Acute Studies of Nesiritide in Decompensated Heart Failure (ASCEND-HF) trial. METHODS AND RESULTS: We explored the association between LVEF and 30 and 180 day mortality in 7007 ADHF patients enrolled in the Acute Studies of Nesiritide in Decompensated Heart Failure (ASCEND-HF) trial. LVEF was analysed both as a continuous variable and according to three categories: < 40% (LowEF), 40-50% [intermediate EF (IntEF)], and > 50% [preserved ejection fraction (PresEF)]. Of the patients in the trial, 4474 (78.7%) had LowEF, 674 (11.9%) had IntEF, and 539 (9.5%) had PresEF. The unadjusted 30 and 180 day mortality was similar for LowEF (3.7%, 12.3%), IntEF (3.4%, 13.1%), and PresEF (4.3%, 14.1%), respectively (P > 0.05). After multivariable adjustment, the hazard ratio (HR) for 180 day mortality remained similar for the LowEF [HR 0.96, 95% confidence interval (CI) 0.75-1.24; P = 0.77] and IntEF (0.91, 95% CI 0.66-1.3; P = 0.58) compared to PresEF patients. By contrast, when LVEF was evaluated as a continuous measure, it exhibited a U-shaped pattern with mortality. After matching for age and sex, the mortality risk attributed to LVEF was attenuated, as the LVEF increased as a continuous variable over 35%. However, in patients with EF < 35%, the mortality risk continue to increase as the LVEF declined. CONCLUSIONS: Among patients with ADHF, the unadjusted mortality rates are similar across LVEF strata. However, after accounting for key patient variables, the mortality risk increases as EF falls below 35%. These data will be useful in planning future studies of ADHF. CLINICAL TRIAL REGISTRATION: www.clinicaltrials.gov identifier: NCT00475852.
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| 8. |
- McConnell, M. L., et al.
(författare)
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POET : A SMEX mission for gamma ray burst polarimetry
- 2014
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 9144
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Tidskriftsartikel (refereegranskat)abstract
- Polarimeters for Energetic Transients (POET) is a mission concept designed to t within the envelope of a NASA Small Explorer (SMEX) mission. POET will use X-ray and gamma-ray polarimetry to uncover the energy release mechanism associated with the formation of stellar-mass black holes and investigate the physics of extreme magnetic ields in the vicinity of compact objects. Two wide-FoV, non-imaging polarimeters will provide polarization measurements over the broad energy range from about 2 keV up to about 500 keV. A Compton scatter polarimeter, using an array of independent scintillation detector elements, will be used to collect data from 50 keV up to 500 keV. At low energies (215 keV), data will be provided by a photoelectric polarimeter based on the use of a Time Projection Chamber for photoelectron tracking. During a two-year baseline mission, POET will be able to collect data that will allow us to distinguish between three basic models for the inner jet of gamma-ray bursts.
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