| 1. |
- Kamae, Tuneyoshi, et al.
(författare)
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PoGOLite - A high sensitivity balloon-borne soft gamma-ray polarimeter
- 2008
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 30:2, s. 72-84
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Tidskriftsartikel (refereegranskat)abstract
- We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 and 80 keV in one 6-h flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow Held of view (FWHM = 1.25 msr, 2.0 deg x 2.0 deg) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (similar to 228 cm(2) at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm(2) indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a similar to 100 mCrab source between 25 and 50 keV. A 6-h observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter.
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| 2. |
- Ylinen, Tomi, et al.
(författare)
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Detecting dark matter annihilation lines with Fermi
- 2008
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Ingår i: Proc. Sci..
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Konferensbidrag (refereegranskat)abstract
- Dark matter constitutes one of the most intriguing but so far unresolved issues in physics today. In many extensions of the Standard Model the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent dark matter particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a "smoking gun" for dark matter, since no other known astrophysical process should be able to produce it. In these proceedings we give an overview of the different approaches to a search for dark matter lines that the Fermi-LAT collaboration is pursuing and the various challenges involved.
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| 3. |
- Ylinen, Tomi
(författare)
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Towards detecting lines from dark matter annihilations with GLAST
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and will manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. When searching for a line, the energy resolution and performance of the calorimeter are key factors. In this thesis, these are investigated using beam test data, taken at CERN in 2006. Four statistical methods that can be used to search for DM spectral lines are, then, studied in terms of their power and coverage. The methods are based on both hypothesis tests and confidence interval calculations. Two peak finding methods are also tested on a simulated data set representing one year of realistic data, obtained with the Large Area Telescope (LAT) on-board the Gamma-ray Large Area Space Telescope (GLAST). The data set is called Service Challenge 2 (SC2) and contains a variety of gamma-ray sources, including different DM components. Finally, an upper limit on < σν > γγ, based on SC2, is calculated.
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