The MAXI mission on the International Space Station

Monitor of All-sky X-ray Image (MAXI) is the first astrophysical payload which will be mounted on the Japanese Experiment Module (JEM) Exposed Facility of International Space Station (ISS) in 2004. It is designed for monitoring all-sky in the X-ray band by scanning with slat collimators and slit apertures. Its angular resolution and scanning period are similar to 1arc degree and 90 minutes, respectively. MAXI employs two types of X-ray camera. One is Gas slit Camera (GSC), the detectors of which are one-dimensional position sensitive proportional counters. Its position resolution is similar to 1.0 mm along carbon anode wires. GSC covers the 2.0-30heV energy band. We have found an interesting feature in the energy response: monochromatic X-rays are detected with a peculiar hard tail in the spectra. The physical mechanism causing the hard tail is still unclear. The other camera is Solid-state Slit Camera (SSC). We employ a pair of SSCs, each of which consists of sixteen CCD chips. Each CCD has 1024x1024 pixels, and each pixel is 24x24 micrometers. The CCDs are to be operated at -60 degree using Peltier coolers. SSC covers an energy range of 0.5-10.0keV. The test counters and test chips are evaluated in NASDA, Riken, and Osaka-University. The continuous Ethernet down Link will enables us to alert the astronomers in all over the world to the appearance of X-ray transients, novae, bursts, nares etc. In this paper we will report on the current status of the MAXI mission.