Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite

M. Axelsson, O. Engdegård, F. Ryde, S. Larsson, M. Pearce, L. Hjalmarsdotter, M. Kiss, C. Marini Bettolo, M. Arimoto, C. I. Björnsson, P. Carlson, Y. Fukazawa, T. Kamae, Y. Kanai, J. Kataoka, N. Kawai, W. Klamra, G. Madejski, T. Mizuno, J. NgH. Tajima, T. Takahashi, T. Tanaka, M. Ueno, G. Varner, K. Yamamoto

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)327-337
Number of pages11
JournalAstroparticle Physics
Volume28
Issue number3
DOIs
Publication statusPublished - 2007 Nov 1
Externally publishedYes

Keywords

  • Compton technique
  • Gamma-rays
  • Geant4
  • PoGOLite
  • Polarization
  • Simulations
  • X-rays

ASJC Scopus subject areas

  • Astronomy and Astrophysics

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    Axelsson, M., Engdegård, O., Ryde, F., Larsson, S., Pearce, M., Hjalmarsdotter, L., Kiss, M., Bettolo, C. M., Arimoto, M., Björnsson, C. I., Carlson, P., Fukazawa, Y., Kamae, T., Kanai, Y., Kataoka, J., Kawai, N., Klamra, W., Madejski, G., Mizuno, T., ... Yamamoto, K. (2007). Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite. Astroparticle Physics, 28(3), 327-337. https://doi.org/10.1016/j.astropartphys.2007.06.006