In spire of extensive efforts of the spectral and lightcurve observations,the emission mechanism of γ-ray bursts(GRBs)is still unclear．Recently the observational techniques of X-ray and γ-ray polarizations have been developed rapidly,and several satellites witb high sensitivity for such high energy polarizations have been planned．They will provide us the firstdefinitive detections of GRB polarizations and enable us to discuss their statistical properties．We calculate the distributionof GRB polarizations in the synchrotron models (with globally ordered magnetic field and with small-scale random magneticfield) and Compton drag model．The results show that the distribution of the polarization degrees of～100 bursts detected by arealistic polarimeter satellite,such as POET,may distinguish the three models,and provide direct diagnostics of the emissionmechanism,the magnetic field configuration,and the geometry of GRB outflows．
Division of Theoretical Astronomy,National Astronomical Observatory of Japan,2-21-1 Osawa,Mitaka,Tok NASA Goddard Space Flight Center,Greenbelt,MD 20771 Department of Physics and Astronomy,University of Nevada Las Vegas,Las Vegas,NV 89154,USA Department of Physics,Hiroshima University,Higashi-Hiroshima,Hiroshima 739-8526,Japan Theory Division,KEK(High Energy Accelerator Research Organization),1-1 Oho,Tsukuba 305-0801,Japan Department of Physics,Kyoto University,Kyoto 606-8502,Japan