Hard X-ray Polarization Measurements on Crab Nebula and Cygnus X-1

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The aim of the research program has been to mount the hard X-ray polarimeter (PoGOLite) we produced with other funds onto a gondola in ESRANGE balloon station in Sweden, and to carry out one-week-long observations of Crab Nebula and Cygnus X-1 onboard a balloon. The polarimeter, control system, and gondola assembly have been built on funds and grants from Stanford Univ., Wallenberg Foundation, JSPS and Swedish Space Board. Two possible long-duration flight routes have been considered: the shorter one is one-week-long flight from Sweden to northern Canada and the longer one is three-week-long circumnavigation around the North Pole. The polarimeter is most sensitive between 20keV and 60keV and capable of detecting 3% polarization in the energy band for Crab Nebula and Cyg X-1 in the hard state. Successful detection of polarization in the targets in the energy range will unravel the emission mechanism and the orientation of the magnetic field at the hard X-ray sources. So far no high accuracy measurement has been made in the energy range. The funds will be used to support Japanese collaboration members to participate in the balloon flight and data analyses.