| 1. |
- Axelsson, Magnus, et al.
(författare)
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GRB110721A : AN EXTREME PEAK ENERGY AND SIGNATURES OF THE PHOTOSPHERE
- 2012
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Ingår i: Astrophysical Journal Letters. - 2041-8205. ; 757:2
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Tidskriftsartikel (refereegranskat)abstract
- GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The burst consisted of one major emission episode which lasted for similar to 24.5 s (in the GBM) and had a peak flux of (5.7 +/- 0.2) x 10(-5) erg s(-1) cm(-2). The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum. The peak energy of the Band component was initially 15 +/- 2 MeV, which is the highest value ever detected in a GRB. This measurement was made possible by combining GBM/BGO data with LAT Low Energy events to achieve continuous 10-100 MeV coverage. The peak energy later decreased as a power law in time with an index of -1.89 +/- 0.10. The temperature of the blackbody component also decreased, starting from similar to 80 keV, and the decay showed a significant break after similar to 2 s. The spectrum provides strong constraints on the standard synchrotron model, indicating that alternative mechanisms may give rise to the emission at these energies.
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| 2. |
- Werren, John H, et al.
(författare)
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Functional and evolutionary insights from the genomes of three parasitoid Nasonia species.
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 327:5963, s. 343-8
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Tidskriftsartikel (refereegranskat)abstract
- We report here genome sequences and comparative analyses of three closely related parasitoid wasps: Nasonia vitripennis, N. giraulti, and N. longicornis. Parasitoids are important regulators of arthropod populations, including major agricultural pests and disease vectors, and Nasonia is an emerging genetic model, particularly for evolutionary and developmental genetics. Key findings include the identification of a functional DNA methylation tool kit; hymenopteran-specific genes including diverse venoms; lateral gene transfers among Pox viruses, Wolbachia, and Nasonia; and the rapid evolution of genes involved in nuclear-mitochondrial interactions that are implicated in speciation. Newly developed genome resources advance Nasonia for genetic research, accelerate mapping and cloning of quantitative trait loci, and will ultimately provide tools and knowledge for further increasing the utility of parasitoids as pest insect-control agents.
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| 3. |
- Greiner, J., et al.
(författare)
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GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy
- 2012
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 34:2, s. 551-582
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Tidskriftsartikel (refereegranskat)abstract
- We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range (COMPTEL, INTEGRAL; see Fig. 1). These gamma-ray observations will be complemented by observations in the soft X-ray and (near-)infrared region with the corresponding telescopes placed on a separate satellite. The Gamma-Ray Imaging, Polarimetry and Spectroscopy ("GRIPS") mission with its three instruments Gamma-Ray Monitor (GRM), X-Ray Monitor (XRM) and InfraRed Telescope (IRT) addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate γ-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.
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| 4. |
- Burgess, J. Michael, et al.
(författare)
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AN OBSERVED CORRELATION BETWEEN THERMAL AND NON-THERMAL EMISSION IN GAMMA-RAY BURSTS
- 2014
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 784:2
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Tidskriftsartikel (refereegranskat)abstract
- Recent observations by the Fermi Gamma-ray Space Telescope have confirmed the existence of thermal and non-thermal components in the prompt photon spectra of some gamma-ray bursts (GRBs). Through an analysis of six bright Fermi GRBs, we have discovered a correlation between the observed photospheric and non-thermal gamma-ray emission components of several GRBs using a physical model that has previously been shown to be a good fit to the Fermi data. From the spectral parameters of these fits we find that the characteristic energies, E-p and kT, of these two components are correlated via the relation E-p proportional to T-alpha which varies from GRB to GRB. We present an interpretation in which the value of the index alpha indicates whether the jet is dominated by kinetic or magnetic energy. To date, this jet composition parameter has been assumed in the modeling of GRB outflows rather than derived from the data.
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| 5. |
- Pe’Er, A., et al.
(författare)
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The Connection Between Thermal and Non-Thermal Emission in Gamma-ray Bursts : General considerations and GRB090902B as a Case Study
- 2011
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Ingår i: GAMMA RAY BURSTS 2010. American Institute of Physics Conference Series. - : AIP. - 9780735409163 ; , s. 91-94
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Photospheric (thermal) emission is inherent to the gamma-ray burst (GRB) “fireball” model. We show that inclusion of this component in the analysis of the GRB prompt emission phase naturally explains some of the prompt GRB spectra seen by the Fermi satellite over its entire energy band. The sub-MeV peak is explained as multi-color black body emission, and the high energy tail, extending up to the GeV band, results from roughly similar contributions of synchrotron emission, synchrotron self Compton (SSC) and Comptonization of the thermal photons by energetic electrons originating after dissipation of the kinetic energy above the photosphere. We briefly discuss the theory of multicolor black body emission from relativistically expanding plasma, before showing how the analysis method proposed results in a complete, self consistent picture of the physical conditions at both emission sites of the thermal and non-thermal radiation. Furthermore, it enables to extract the values of the free model parameters. We demonstrate the analysis method on GRB090902B, and present the values of the physical parameters deduced. We briefly discuss the uniqueness of GRB090902B-type spectra.
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| 6. |
- Pe’Er, A., et al.
(författare)
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The connection between thermal and non-thermal emission in gamma-ray bursts : general considerations and GRB090902B as a case study
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 420:1, s. 468-482
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Tidskriftsartikel (refereegranskat)abstract
- Photospheric (thermal) emission is inherent to the gamma-ray burst (GRB) 'fireball' model. We show here that inclusion of this component in the analysis of the GRB prompt emission phase naturally explains some of the prompt GRB spectra seen by the Fermi satellite over its entire energy band. The sub-MeV peak is explained as multicolour blackbody emission, and the high-energy tail, extending up to the GeV band, results from roughly similar contributions of synchrotron emission, synchrotron self-Compton and Comptonization of the thermal photons by energetic electrons originating after dissipation of the kinetic energy above the photosphere. We show how this analysis method results in a complete, self-consistent picture of the physical conditions at both emission sites of the thermal and non-thermal radiation. We study the connection between the thermal and non-thermal parts of the spectrum, and show how the values of the free model parameters are deduced from the data. We demonstrate our analysis method on GRB090902B: we deduce a Lorentz factor in the range 920 <= eta <= 1070, photospheric radius r(ph) similar or equal to 7.2-8.4 x 10(11) cm and dissipation radius r(gamma) >= 3.5-4.1 x 10(15) cm. By comparison to afterglow data, we deduce that a large fraction epsilon(d) approximate to 85-95 per cent of the kinetic energy is dissipated, and that a large fraction, similar to equipartition of this energy, is carried by the electrons and the magnetic field. This high value of epsilon(d) questions the 'internal shock' scenario as the main energy dissipation mechanism for this GRB.
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