ANIR: Infrared-Optical Simultaneous Imager for miniTAO 1 m Telescope at an Altitude of 5640 m

Early follow-up observations of gamma-ray bursts (GRBs) in wide wavelength range, especially from the optical to the near infrared (NIR) bands, are crucial for search of high-redshift GRBs by detecting their Lyman limit break. For this purpose, we have developed a NIR/optical simultaneous imager called ANIR (Atacama Near InfraRed camera) for the University of Tokyo Atacama 1.0 m telescope. Installed at the summit of Co. Chajnantor (5640 m altitude) in northern Chile, this telescope is the world's highest optical/NIR observatory. ANIR saw the first light in June 2009, and several observing runs have been carried out for performance verification as well as scientific observations. During the run, we have successfully detected an optical/NIR afterglow of GRB091018. Thanks to the excellent seeing (median ∼0''.8), 5σ limiting magnitudes reach 23.3, 20.6, and 20.8 mag(AB) in the B, J and Ks bands, respectively, with 600 sec exposure.