Optical properties of the fluorescence detector in the Telescope Array experiment using the Opt-copter

The Opt-copter was developed as a calibration device for the FDs. The Opt-copter is equipped with a UV LED light source and a Real-Time Kinematic GPS (RTK-GPS) module for precise positioning. Using the Opt-copter, the pointing direction analysis of all 38 TA-FDs at the three stations has been completed using the Opt-copter. As a result, the elevation shifts showed different tendencies at each station. Similar shifts were observed among FDs pointing in similar directions, even if located at different stations about 35 km apart. This suggests that systematic effects may have been introduced by the types and motions of stars observed by FDs. The overall uncertainty of this analysis was estimated to be 0.03°.