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Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
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2007 (English)In: Astroparticle Physics, Vol. 28, no 3, 327-337 p.Article in journal (Refereed) Published
Abstract [en]

Linear polarization in X- and γ-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper, we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25–100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 h were simulated, corresponding to a standard and a long duration flight, respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.

Place, publisher, year, edition, pages
2007. Vol. 28, no 3, 327-337 p.
Keyword [en]
Polarization, X-rays, Gamma-rays, Compton technique, PoGOLite, Geant4, Simulations
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-19575DOI: doi:10.1016/j.astropartphys.2007.06.006OAI: diva2:186099
Available from: 2008-01-14 Created: 2008-01-14 Last updated: 2011-01-11Bibliographically approved

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Axelsson, MagnusLarsson, StefanHjalmarsdotter, LinneaBjörnsson, Claes-Ingvar
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