Chikara Natsukari

Soft x-ray imager (SXI) onboard ASTRO-H

Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched in 2015. The SXI camera contains four CCD chips, each with an imaging area of 31mm x 31 mm, arrayed in mosaic, covering the whole FOV area of 38′ x 38′. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200 _m. High QE of 77% at 10 keV expected for this device is an advantage to cover an overlapping energy band with the Hard X-ray Imager (HXI) onboard ASTRO-H. Most of the flight components of the SXI system are completed until the end of 2013 and assembled, and an end-to-end test is performed. Basic performance is verified to meet the requirements. Similar performance is confirmed in the first integration test of the satellite performed in March to June 2014, in which the energy resolution at 5.9 keV of 160 eV is obtained. In parallel to these activities, calibrations using engineering model CCDs are performed, including QE, transmission of a filter, linearity, and response profiles.

Fast and flexible CCD-driver system using fast DAC and FPGA

Abstract 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 an electrical short between high and low levels 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 ( ∼10 MHz ) 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 Field Programmable Gate Array (FPGA) 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 K α has a full-width at half-maximum of ≃150 eV and the readout noise of our system is ≃8e − .

Developments of engineering model of the X-ray CCD camera of the MAXI experiment onboard the International Space Station

Abstract MAXI, Monitor of All-sky X-ray Image, is an 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 0.5– 30 keV . We have developed an engineering model (EM) for all components of the SSC. Their performance test is underway. We have also developed several kinds of CCDs fabricated from different wafers. Since the thermal condition of the ISS is not suitable for the CCD operation, the operating temperature of the CCD is estimated to be −85° to −50°C at the end of mission life. We therefore carefully need to choose CCD considering not only detection efficiency and readout noise but also the dark current. Here we report the current status of the EM of the SSC and the X-ray responsivity of CCDs.

Vibration isolation system for cryocoolers of Soft X-ray Spectrometer (SXS) onboard ASTRO-H (Hitomi)

Soft X-ray Spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from micro-vibration from cryocoolers mounted on the dewar. This is mitigated for the flight model by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the flight model was verified before launch of the spacecraft in both ambient condition and thermal-vac condition, showing no detectable degradation in energy resolution. The in-orbit performance was also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the micro-vibration could degrade the cryogenic detector is shown.

The Soft X-ray Imager (SXI) for the ASTRO-H Mission

The Soft X-ray Imager (SXI) is an X-ray CCD camera onboard the ASTRO-H X-ray observatory. The CCD chip used is a P-channel back-illuminated type, and has a 200-µm thick depletion layer, with which the SXI covers the energy range between 0.4 keV and 12 keV. Its imaging area has a size of 31 mm x 31 mm. We arrange four of the CCD chips in a 2 by 2 grid so that we can cover a large field-of-view of 38’ x 38’. We cool the CCDs to -120 °C with a single-stage Stirling cooler. As was done for the CCD camera of the Suzaku satellite, XIS, artificial charges are injected to selected rows in order to recover charge transfer inefficiency due to radiation damage caused by in-orbit cosmic rays. We completed fabrication of flight models of the SXI and installed them into the satellite. We verified the performance of the SXI in a series of satellite tests. On-ground calibrations were also carried out and detailed studies are ongoing.

Soft x-ray imager onboard ASTRO-H

The Soft X-ray Imager, SXI, is an X-ray CCD camera onboard the ASTRO-H satellite to be launched in 2015. ASTRO-H will carry two types of soft X-ray detector. The X-ray calorimeter, SXS, has an excellent energy resolution with a narrow field of view while the SXI has a medium energy resolution with a large field of view, 38′ square. We employ 4 CCDs of P-channel type with a depletion layer of 200 μm. Having passed the CDR, we assemble the FM so that we can join the final assembly. We present here the SXI status and its expected performance in orbit.

Developments of CCDs and relevant electronics for the x-ray CCD camera of the MAXI experiment onboard the International Space Station

MAXI, Monitor of All-sky X-ray Image, is an 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 approximately 5000 cm2, the Gas Slit Camera (GSC), and the other is an X-ray CCD array with a total area approximately 200 cm2, the Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular dimension of 1 degree(s) times 180 degree(s) while the SSC subtends a field of view with an angular dimension of 1 degree(s) times a little less than 180 degree(s). In the course of one station orbit,MAXI can scan almost the entire sky with a precision of 1 degree(s) and with an X-ray energy range of 0.5- 30keV. We have developed an engineering model (EM) for all components of the SSC. Their performance test is ongoing. We have also developed several kinds of CCDs fabricated from different wafers. Since the thermal condition of the ISS is not suitable for the CCD operation, the operating temperature of the CCD estimated to be -85 approximately -50 degree(s) at the end of mission life. We therefore carefully need to choose CCD considering not only detection efficiency and readout noise but also the dark current. We report here the current status of the EM of the SSC and the X-ray responsibity of CCDs.

Performance and calibration of the x-ray CCD camera of the MAXI experiment on the ISS/JEM

We have developed an engineering model of CCD chips and the analogue electronics for the Solid-state Slit Camera. To optimize its X-ray responsibility, we have also developed a flexible general-purpose CCD data acquisition system. We tested many kinds of clock patterns with different voltage levels. We report here our new CCD system and preliminary results of optimization of clock voltages.

Vibration isolation system for cryocoolers of soft x-ray spectrometer on-board ASTRO-H (Hitomi)

Abstract. The soft x-ray spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from microvibration from cryocoolers mounted on the dewar. This is mitigated for the flight model (FM) by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the FM was verified before launch of the spacecraft in both ambient condition and thermal-vacuum condition, showing no detectable degradation in energy resolution. The in-orbit detector spectral performance and cryocooler cooling performance were also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the microvibration could degrade the cryogenic detector is shown. Lessons learned from the development to mitigate unexpected issues are also described.

Design of the time assignment system for ASTRO-H and its performance before launch

The ASTRO-H, which will be launched in 2015, is the sixth in a series of Japanese X-ray satellites. It is an international mission led by JAXA in collaboration with NASA and ESA, aiming to observe astrophysical objects in the X-ray band from 0.5 to 600 keV. One of the important scientific goals is to understand physical processes in the extreme environments of active and variable astrophysical objects, such as black holes, neutron stars, binary star, and active galactic nuclei. Therefore, a fast timing capability is a key requirement for the mission. According to numerical estimates of scientific performance, absolute times of X-ray events are required to have an accuracy of 300 μs to achieve minimum scientific goals and an accuracy of 30 μs is desired as a goal. The satellite carries a GPS receiver to get the accurate time information, which is distributed from the central computer on board through the large-and-complex SpaceWire network. Distributions of time information are shared in the same lines used for communications of telemetry and commands, and thus propagation delays and jitters affect the timing accuracy of the payload instruments. Further six items are identified as sources of timing errors and are measured on ground to be used in the calibration by off-line software. The time-assignment tasks in the off-line software packages are designed to be common for all the scientific instruments, although the hardware designs for finer timing resolutions are different by the instruments. Measurements of propagation delays in the flight configuration on ground and in-orbit calibration plans are described. The detail description will be submitted to the IEEE TNS paper in near future. This work demonstrates a good example of care points for space-use instruments in the hardware-and-software designs and calibration measurements in order to achieve a fine timing resolution at the micro second order with the middle-sized satellites using the SpaceWire (IEEE1355) network.