In Orbit Performance of the MAXI/SSC onboard the ISS

We report here the in orbit performance of the CCD camera (MAXI/SSC) onboard the International Space Station (ISS). It was commissioned in August, 2009. This is the first all-sky survey mission employing X-ray CCDs. It consists of 32 CCDs each of which is 1 inch square. It is a slit camera with a field of view of 1deg.5x 90deg and scans the sky as the rotation of the ISS. The CCD on the SSC is cooled down to the working temperature around -60degC by the combination of the peltier cooler, a loop heat pipe and a radiator. The standard observation mode of the CCD is in a parallel sum mode (64-binning). The CCD functions properly although it suffers an edge glow when the Sun is near the field of view (FOV) which reduces the observation efficiency of the SSC down to about 30%. The performance of the CCD is continuously monitored both by the Mn-K X-rays and by the Cu-K X-rays. There are many sources detected, not only point sources but extended sources. Due to the lack of the effective observation time, we need more observation time to obtain an extended emission analysis extraction process.Comment: 15 pages 11 figure

Proton Irradiation Experiment for the X-ray Charge-Coupled Devices of the Monitor of All-sky X-ray Image mission onboard the International Space Station: I. Experimental Setup and Measurement of the Charge Transfer Inefficiency

We have investigated the radiation damage effects on a CCD to be employed in the Japanese X-ray astronomy mission including the Monitor of All-sky X-ray Image (MAXI) onboard the International Space Station (ISS). Since low energy protons release their energy mainly at the charge transfer channel, resulting a decrease of the charge transfer efficiency, we thus focused on the low energy protons in our experiments. A 171 keV to 3.91 MeV proton beam was irradiated to a given device. We measured the degradation of the charge transfer inefficiency (CTI) as a function of incremental fluence. A 292 keV proton beam degraded the CTI most seriously. Taking into account the proton energy dependence of the CTI, we confirmed that the transfer channel has the lowest radiation tolerance. We have also developed the different device architectures to reduce the radiation damage in orbit. Among them, the ``notch'' CCD, in which the buried channel implant concentration is increased, resulting in a deeper potential well than outside, has three times higher radiation tolerance than that of the normal CCD. We then estimated the charge transfer inefficiency of the CCD in the orbit of ISS, considering the proton energy spectrum. The CTI value is estimated to be 1.1e-5 per each transfer after two years of mission life in the worse case analysis if the highest radiation-tolerant device is employed. This value is well within the acceptable limit and we have confirmed the high radiation-tolerance of CCDs for the MAXI mission.Comment: 17 pages, 2 table, 12 figures. Accepted for publication of Japanese Journal of Applied Physics. High resolution file is available from http://wwwxray.ess.sci.osaka-u.ac.jp/~miyata/paper/proton_cti.pd

Solid-state Slit Camera (SSC) on Board MAXI

Abstract Solid-state Slit Camera (SSC) is an X-ray camera onboard the MAXI mission of the International Space Station. Two sets of SSC sensors view X-ray sky using charge-coupled devices (CCDs) in 0.5-12 keV band. The total area for the X-ray detection is about 200 cm 2 which is the largest among the missions of X-ray astronomy. The energy resolution at the CCD temperature of −70 • C is 145 eV in full width at the half maximum (FWHM) at 5.9 keV, and the field of view is 1 • .5 (FWHM) × 90 • for each sensor. The SSC could make a whole-sky image with the energy resolution good enough to resolve line emissions, and monitor the whole-sky at the energy band of < 2 keV for the first time in these decades