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| 3. |
- Abramowski, A., et al.
(författare)
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Search for extended gamma-ray emission around AGN with HESS and Fermi-LAT
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 562, s. A145-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Very-high-energy (VHE; E > 100 GeV) gamma-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these gamma-rays with the extragalactic background light (EBL). Depending on the magnetic fields in the proximity of the source, the cascade initiated from pair production can result in either an isotropic halo around an initially- beamed source or a magnetically- broadened cascade :aux. Aims. Both extended pair-halo (PH) and magnetically broadened cascade (MBC) emission from regions surrounding the blazars 1ES 1101-232, IRS 0229+200, and PKS 2155-304 were searched for using VHE y-ray data taken with the High Energy Stereoscopic System (HESS.) and high-energy (HE; 100 MeV < E < 100 GeV) gamma-ray data with the Fermi Large Area Telescope (LAT). Methods. By comparing the angular distributions of the reconstructed gamma-ray events to the angular profiles calculated from detailed theoretical models, the presence of PH and MBC was investigated. Results. Upper limits on the extended emission around lES 1101-232, lES 0229+200, and PKS 2155-304 are found to be at a level of a few per cent of the Crab nebula flux above 1 TeV, depending on the assumed photon index of the cascade emission. Assuming strong extra-Galactic magnetic field (EGME) values, >10(-12) G, this limits the production of pair haloes developing from electromagnetic cascades. For weaker magnetic fields, in which electromagnetic cascades would result in MBCs. EGMF strengths in the range (0.3-3) x 10(-15) G were excluded for PKS 2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence length.
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| 4. |
- Fernqvist, Stina, et al.
(författare)
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Economic hardship in childhood : Children's agency in processes concerning families with scarce resources
- 2006
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Konferensbidrag (populärvet., debatt m.m.)abstract
- This paper presents some theoretical discussions and initial empirical results from a research project aiming at analysing children’s experiences of living in economic hardship in Sweden. The newly started project is focusing on children´s own perspective, their experiences in everyday life in various social contexts, and their financial and social strategies in interaction with other children, their parents and professionals at school and in the social welfare agencies. What does economic hardship mean to children in terms of material conditions, social relations, school work, identity or wellbeing? Which scope of agency do children see and how do they use it? How do the legal framework and the practices at school and at social welfare agencies construct the child (of various age and gender), the mother and the father in this kind of cases? Are children seen as actors, victims, consumers or objects of their parents responsibility as providers? Are children allowed a scope of action in the financial decision making processes in their family and / or in the welfare agencies? If so, what kind of agency and what happens when they participate? Which kind of interpretative framework concerning children’s actions is used by the adults involved in the interaction with the children? This paper will present initial findings from analyses of the legal processes concerning social welfare to families with children, focusing on the eventual scope of agency for children. The empirical work is conducted in two different municipalities in Sweden and will include interviews and a survey with children from three age categories (6-7, 11-12, 15-16), their parents (single as well as two parent families), school staff and social welfare officers. The project draws on childhood sociology, and research on gender, organization and professions.
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- Klintenberg, Patrik
(författare)
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More Water, Less Grass? : An assessment of resource degradation and stakeholders’ perceptions of environmental change in Ombuga Grassland, Northern Namibia
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objectives of this thesis are to assess: to what degree have natural resources deteriorated in a grazing area in northern Namibia, how do perceptions of environmental change held by local stakeholders there, correspond to scientific assessments, and how do these relate to national estimates? Analysis of the process of developing national indicators for monitoring of land degradation concluded that specific indicators should be developed on national level, and in some instances even on local level as there are no universal causes of land degradation. According to farmers overgrazing and low rainfall since the early 1990s cause negative environmental changes in the study area, partly confirming findings from national monitoring. Results also suggest that: less grazing outside the study area, improved access, permanent water supply, and fencing of large areas, also contributed. Results show that improved water supply was the most important factor. Investigation of the influence of permanent water points on grazing resources showed that perennial grasses are replaced by less palatable annual grasses as far as 6 km from water points along a water pipeline. No significant grazing induced changes in grass composition were observed around privately owned wells. Private ownership seems to be a key factor preventing over-utilization of grazing resources around the latter. A remote sensing study using Landsat TM imagery identified bare ground, saltpans and grassland with a fair accuracy. Separation of woodland from shrubland and shrubland from grassland was less accurate using supervised classification. The results show that the soil adjusted vegetation index provides valuable information about variations of green biomass over time in semi-arid environments. However, it is suggested that satellite based investigations should be supported by thorough ground based assessment due to the influence of underlying soil in this environment.
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| 6. |
- Abdo, A. A., et al.
(författare)
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The on-orbit calibration of the Fermi Large Area Telescope
- 2009
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 32:3-4, s. 193-219
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Tidskriftsartikel (refereegranskat)abstract
- The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope began its on-orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on-orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.
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| 7. |
- Accettura, Carlotta, et al.
(författare)
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Towards a muon collider
- 2023
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Ingår i: European Physical Journal C. - 1434-6044 .- 1434-6052. ; 83:9
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Forskningsöversikt (refereegranskat)abstract
- A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.
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| 8. |
- Ackermann, M., et al.
(författare)
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CONSTRAINTS ON THE COSMIC-RAY DENSITY GRADIENT BEYOND THE SOLAR CIRCLE FROM FERMI gamma-RAY OBSERVATIONS OF THE THIRD GALACTIC QUADRANT
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 726:2, s. 81-
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Tidskriftsartikel (refereegranskat)abstract
- We report an analysis of the interstellar gamma-ray emission in the third Galactic quadrant measured by the Fermi Large Area Telescope. The window encompassing the Galactic plane from longitude 210 degrees to 250 degrees has kinematically well-defined segments of the Local and the Perseus arms, suitable to study the cosmic-ray (CR) densities across the outer Galaxy. We measure no large gradient with Galactocentric distance of the gamma-ray emissivities per interstellar H atom over the regions sampled in this study. The gradient depends, however, on the optical depth correction applied to derive the H I column densities. No significant variations are found in the interstellar spectra in the outer Galaxy, indicating similar shapes of the CR spectrum up to the Perseus arm for particles with GeV to tens of GeV energies. The emissivity as a function of Galactocentric radius does not show a large enhancement in the spiral arms with respect to the interarm region. The measured emissivity gradient is flatter than expectations based on a CR propagation model using the radial distribution of supernova remnants and uniform diffusion properties. In this context, observations require a larger halo size and/or a flatter CR source distribution than usually assumed. The molecular mass calibrating ratio, X(CO) = N(H(2))/W(CO), is found to be (2.08 +/- 0.11) x 10(20) cm(-2)(K km s(-1))(-1) in the Local arm clouds and is not significantly sensitive to the choice of Hi spin temperature. No significant variations are found for clouds in the interarm region.
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| 9. |
- Ackermann, M., et al.
(författare)
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The cosmic-ray and gas content of the Cygnus region as measured in gamma-rays by the Fermi Large Area Telescope
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 538, s. A71-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Cygnus region hosts a giant molecular-cloud complex that actively forms massive stars. Interactions of cosmic rays with interstellar gas and radiation fields make it shine at gamma-ray energies. Several gamma-ray pulsars and other energetic sources are seen in this direction. Aims. In this paper we analyze the gamma-ray emission measured by the Fermi Large Area Telescope (LAT) in the energy range from 100 MeV to 100 GeV in order to probe the gas and cosmic-ray content on the scale of the whole Cygnus complex. The gamma-ray emission on the scale of the central massive stellar clusters and from individual sources is addressed elsewhere. Methods. The signal from bright pulsars is greatly reduced by selecting photons in their off-pulse phase intervals. We compare the diffuse gamma-ray emission with interstellar gas maps derived from radio/mm-wave lines and visual extinction data. A general model of the region, including other pulsars and gamma-ray sources, is sought. Results. The integral HI emissivity above 100 MeV averaged over the whole Cygnus complex amounts to [2.06 +/- 0.11 (stat.) (+0.15)(-0.84) (syst.)] x 10(-26) photons s(-1) sr(-1) H-atom(-1), where the systematic error is dominated by the uncertainty on the HI opacity to calculate its column densities. The integral emissivity and its spectral energy distribution are both consistent within the systematics with LAT measurements in the interstellar space near the solar system. The average X-CO = N(H-2)/W-CO ratio is found to be [1.68 +/- 0.05 (stat.) (+0.87)(-0.10) (H I opacity)] x 10(20) molecules cm(-2) (K km s(-1))(-1), consistent with other LAT measurements in the Local Arm. We detect significant gamma-ray emission from dark neutral gas for a mass corresponding to similar to 40% of what is traced by CO. The total interstellar mass in the Cygnus complex inferred from its gamma-ray emission amounts to 8 (+5)(-1) x 10(6) M-circle dot at a distance of 1.4 kpc. Conclusions. Despite the conspicuous star formation activity and high masses of the interstellar clouds, the cosmic-ray population in the Cygnus complex averaged over a few hundred parsecs is similar to that of the local interstellar space.
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