We report the in-orbit performance of the Gas Slit Camera (GSC) on the MAXI
(Monitor of All-sky X-ray Image) mission carried on the International Space
Station (ISS). Its commissioning operation started on August 8, 2009, confirmed
the basic performances of the effective area in the energy band of 2--30 keV,
the spatial resolution of the slit-and-slat collimator and detector with 1.5
degree FWHM, the source visibility of 40-150 seconds for each scan cycle, and
the sky coverage of 85% per 92-minute orbital period and 95% per day. The gas
gains and read-out amplifier gains have been stable within 1%. The background
rate is consistent with the past X-ray experiments operated at the similar
low-earth orbit if its relation with the geomagnetic cutoff rigidity is
extrapolated to the high latitude. We also present the status of the in-orbit
operation and the calibration of the effective area and the energy response
matrix using Crab-nebula data.Comment: 11 pages, 14 figures, accepted for publication in PAS