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K. Hayashida, H. Tsunemi, T. Koike, T. Horikawa (Osaka University), F. Makino (NASDA)
X-ray polarimetry has been unexploited field in X-ray astronomy. Detection of the X-ray polarization was succeeded only in a few sources including Crab nebulae at 2.6keV and 5.2keV. In this paper, we present our plan of a balloon experiment of X-ray polarimetry. We will employ conventional Xe gas proportional counters with collimator. We will measure the signal rise time of each event, which reflects polarization direction of the incident X-rays relative to the anode wire direction. Ground experiment revealed that the modulation contrast (M) of this method amounts to about 0.1 at 20keV and 0.35 at 40keV (K. Hayashida et al., 1999, NIMA421, p.241). Different from the scattering method, the large effective area of the gas proportional counters is exploited as it is in this method. We show that a pair of 300 m2 PCs is enough for detecting X-ray polarization of Crab nebulae at 20-60keV range, where no polarization measurement has been done so far.