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X-Ray Polarimetry Workshop SLAC, Stanford, California 9-11 February 2004 |
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Large-Area Balloon-Borne Polarized Gamma Ray Observer (PoGO)
Tuneyoshi
Kamae
SLAC
kamae@slac.stanford.edu
P. Chen, T. Kamae, G. Madejski, J. Ng, T. Mizuno, H. Tajima, T. Thurston(SLAC); L. Barbier, A. Harding, J. Krizmanic, J. Mitchell, R. Streitmatter (NASA-GSFC); E. Groth, R. Fernholz, D. Marlow (Princeton Univ.); G. Bogaert (Ecole Polytechnique); S. Gunji, H. Sakurai (Yamagata Univ.); Y. Saito, T. Takahashi (ISAS); J. Kataoka, N. Kawai (Tokyo Inst. of Technology); Y. Fukazawa (Hiroshima Univ.); P. Carlson, W. Klamra, M. Pearce (Royal Inst. of Technology); S. Larsson (Stockholm Univ.)
PoGO is an instrument to measure the polarization of gamma-rays in the energy range 25-200 keV. Its design is sensitive to <10% polarization of a 100 mCrab source in a single 6-hour balloon observation. PoGO has been selected by NASA as a Research Opportunities in Space Science program. The instrument uses Compton scattering and photo-absorption in an array of 200-400 well-type phoswich detector units, incorporates active and passive collimation to a narrow field-of-view (FOV) of about 5 square-degree, and suppresses background to 10mCrab level. The well-type phoswich detector technology has been adopted in the past in a balloon instrument (Welcome-I) and a satellite experiment (AstroE2-HXD), and proven to reduce external background rate significantly. The instrument has no consumable nor temperature sensitive component: So its adoptation to a satellite prject will be straightforward. A prototype instrument consisting of 7 units has been built and tested in a polarized hard X-ray beam at the Advanced Photon Source of Argonne National Laboratory. The prototype behaved as predicted by computer simulation studies, allowed clean kinematical selection of Compton events, and gave a modulation factor around 41%. Two possible designs of PoGO are now being studied aiming at the first balloon flight in US-Fiscal Year of 2007-2008. The instrument design, the beam test results and the simulation studies will be presented. Included in the presentation will be a comparison between EGS4 with the Namito-Ban-Hirayama implementation of photon polarization and the Geant4 (v.5.1) with the PoGO fix of the photon polarization code.
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For more information, contact
Jennifer Formichelli |
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