Recently, COMPTEL has detected γ-rays of 1157 keV from 44 Ti in the direction of the SNR RX J0852−4622 (Iyudin et al. 1998). Since 44 Ti is a product of explosive nucleosynthesis and its half lifetime τ 1/2 is about 60 yrs, RX J0852−4622 must be a young supernova remnant and radiation is dominated by the ejecta rather than by interstellar matter. We have detected an X-ray emission line at 4.1 ± 0.2 keV which is thought to come from highly ionized Ca. The emission line is so far only seen in the north-west shell region of RX J0852−4622. The X-ray spectrum can be well fitted with that of thin hot plasma of cosmic abundances except that of Ca, which is overabundant by a factor of 8 ± 5. Assuming that most of Ca is 44 Ca, which originates from 44 Ti by radioactive decay, we estimate a total Ca mass of about 1.1 × 10 −3 M ⊙ . Combining the amount of 44 Ca and the observed flux of the 44 Ti γ-ray line, the age of RX J0852−4622 is around 1000 yrs.

We have developed a completely new type of general-purpose CCD data acquisition system which enables one to drive any type of CCD using any type of clocking mode. A CCD driver system widely used before consisted of an analog multiplexer (MPX), a digital-to-analog converter (DAC), and an operational amplifier. A DAC is used to determine high and low voltage levels and the MPX selects each voltage level using a TTL clock. In this kind of driver board, it is difficult to reduce the noise caused by a short of high and low level in MPX and also to select many kinds of different voltage levels.Recent developments in semiconductor IC enable us to use a very fast sampling (∼ 10MHz) DAC with low cost. We thus develop the new driver system using a fast DAC in order to determine both the voltage level of the clock and the clocking timing. We use FPGA (Field Programmable Gate Array) to control the DAC. We have constructed the data acquisition system and found that the CCD functions well with our new system. The energy resolution of Mn Kα has a full-width at half-maximum of ≃ 150 eV and the readout noise of our system is ≃ 8 e − .

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MAXI, Monitor of All-sky X-ray Image, is the X-ray observatory on the Japanese experimental module (JEM) Exposed Facility (EF) on the International Space Station (ISS). MAXI is a slit scanning camera which consists of two kinds of X-ray detectors: one is a one-dimensional position-sensitive proportional counter with a total area of ∼ 5000 cm 2 , the Gas Slit Camera (GSC), and the other is an X-ray CCD array with a total area ∼ 200 cm 2 , the Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular dimension of 1 • × 180 • while the SSC subtends a field of view with an angular dimension of 1 • times a little less than 180 • . In the course of one station orbit, MAXI can scan almost the entire sky with a precision of 1 • and with an X-ray energy range of 0.5−30 keV.We have developed the engineering model of CCD chips and the analogue electronics for the SSC. The energy resolution of EM CCD for Mn Kα has a full-width at half maximum of ≃ 182 eV. Readout noise is ≃ 11 e − rms.