Optimising a balloon-borne polarimeter in the hard X-ray domain: From the PoGOLite Pathfinder to PoGO+ |
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| Affiliation: | 1. KTH Royal Institute of Technology, Department of Physics, Stockholm 106 91, Sweden;2. The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, Stockholm 106 91, Sweden;3. Department of Physical Science, Hiroshima University, Hiroshima 739–8526, Japan;4. Max Planck Institut for Physics, Munich D-80805, Germany;5. University of Geneva, Geneva CH-1211, Switzerland;1. ETH Zurich, Institute for Particle Physics, Otto-Stern-Weg 5, 8093 Zurich, Switzerland;2. University of Geneva, ISDC Data Center for Astrophysics, Chemin d’Ecogia 16, 1290 Versoix, Switzerland;3. Universität Würzburg, Institute for Theoretical Physics and Astrophysics, Emil-Fischer-Str. 31, 97074 Würzburg, Germany;4. TU Dortmund, Experimental Physics 5, Otto-Hahn-Str. 4, 44221 Dortmund, Germany;1. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, Germany;2. Centre for Space Research, North-West University, Potchefstroom, South Africa;1. ITeDA (CNEA, CONICET, UNSAM), Buenos Aires, Argentina;2. Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), Buenos Aires, Argentina;1. Excellence Cluster Universe, Boltzmannstr. 2, Garching, D-85748, Germany;2. Ronin Institute, Montclair, NJ, USA;3. Department of Physics, University of Houston, Houston, TX, USA;1. School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China;2. Collaborative Innovation Center of Quantum Matter, Beijing, China;3. Center for High Energy Physics, Peking University, Beijing 100871, China;4. Center for History and Philosophy of Science, Peking University, Beijing 100871, China |
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| Abstract: | PoGOLite is a balloon-borne hard X-ray polarimeter dedicated to the study of point sources. Compton scattered events are registered using an array of plastic scintillator units to determine the polarisation of incident X-rays in the energy range 20–240 keV. In 2013, a near circumpolar balloon flight of 14 days duration was completed after launch from Esrange, Sweden, resulting in a measurement of the linear polarisation of the Crab emission. Building on the experience gained from this Pathfinder flight, the polarimeter is being modified to improve performance for a second flight in 2016. Such optimisations, based on Geant4 Monte Carlo simulations, take into account the source characteristics, the instrument response and the background environment which is dominated by atmospheric neutrons. This paper describes the optimisation of the polarimeter and details the associated increase in performance. The resulting design, PoGO+, is expected to improve the Minimum Detectable Polarisation (MDP) for the Crab from 19.8% to 11.1% for a 5 day flight. Assuming the same Crab polarisation fraction as measured during the 2013 flight, this improvement in MDP will allow a 5σ constrained result. It will also allow the study of the nebula emission only (Crab off-pulse) and Cygnus X-1 if in the hard state. |
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