Expected performance of the PHENEX polarimeter by enlargement of detection area

We have been developing a hard X-ray polarimeter with high sensitivity, called as a PHENEX (Polarimetry for High ENErgy X rays) polarimeter. We constructed prototype PHENEX polarimeter and carried out a preliminary observation of the Crab Nebula on Jun. 13th 2006 as a balloon-borne experiment. Though we confirmed from the data that PHENEX polarimeter detected hard X rays from the Crab Nebula with a significance of 8σ, the degree and the direction of polarization with high accuracy could not be determined because of the trouble for attitude control system (ACS) and the small detection area of the prototype polarimeter. Now we are fixing the ACS trouble and improving the detector to realize the observation of the Crab Nebula with higher accuracy in the next balloon-borne experiment. In this paper, we will mainly explain about the improvement of the PHENEX polarimeter and present the expected performance for the next observation.