In this paper, we present the gap detector and its ground and onboard calibrations. Gap is a small instrument with the net weight of 4.0 kg, but we will perform reliable polarimetry with the systematic uncertainty of a few % level due to the high symmetric structure and the capability of coincidence event sampling. Therefore, we are able to obtain time resolved polarization data.
Previously, a few of the grb polarization detections were reported This time, our detector works fully in the coincidence mode to avoid the confusion. Although they used the compton scattering method, but their measurements were non‐coincidence mode
