Search

We have been developing P-channel Charge-Coupled Devices (CCDs) for the upcoming X-ray Astronomy Satellite XRISM, planned to be launched in 2021. While the basic design of the CCD camera (Soft X-ray Imager: SXI) is almost the same as that of the lost Hitomi (ASTRO-H) observatory, we are planning to reduce the "light leakages" that is one of the largest problems recognized in Hitomi data. We adopted a double-layer optical blocking layer on the XRISM CCDs and also added an extra aluminum layer on the backside of them. We develop a newly designed test sample CCD and irradiate it with optical light to evaluate the optical blocking performance. As a result, light leakages are effectively reduced compared with that of the Hitomi CCDs. We thus conclude that the issue is solved by the new design and that the XRISM CCDs satisfy the mission requirement for the SXI., 6 pages, 4 figures, accepted for publication in NIMA, proceedings of the 12th International "Hiroshima" Symposium on the Development and Application of Semiconductor Tracking Detector (HSTD12)

P-channel charge-coupled devices (CCDs) made from N-type silicon wafers were originally developed for ground-based optical and near-infrared telescopes. The thick depletion layer of these CCDs provides the significant advantage of high quantum efficiency (QE) for hard X-rays. On the other hand, high QE for soft X-rays is obtained with back-illuminated (BI) and fully depleted CCDs in which only a thin dead layer exists on the surface of incidence. Thus, P-channel BI CCDs can be applicable as superior wide band X-ray detectors. We have developed such a device specifically for the Soft X-ray Imager (SXI) on board the X-ray astronomy satellite ASTRO-H, scheduled to be launched in 2014. We previously reported that the depletion layers of our CCDs, a prototype of SXI-CCDs, have a thickness of more than 200 μ m . In this paper, we report a novel soft X-ray response of P-channel BI CCDs. First, we irradiate fluorescent X-rays of O, F, Na, Al, Si and K to the SXI prototype. This experiment reveals that our CCD has a significant low-energy tail structure in the soft X-ray response. Since the intensity of the low-energy tail is larger for lower X-ray energies, the tail is originated on the CCD surface layer. Then, we fabricate a new type of CCDs by applying an alternative treatment to its surface layer. The soft X-ray response of the CCD is measured by irradiation of monochromatic X-rays from 0.25 keV to 1.8 keV in a synchrotron facility, KEK-PF. The intensity of the low-energy tail for 0.5 keV incident X-ray is one order of magnitude smaller than that for the previous CCD. The same treatment will be applied to the surface layer of the SXI flight model.

Although our Galactic Center harbors a black hole (Sgr A*) of a few million solar masses, it and its environments are very quiet at present. In X-rays however, the close vicinity of Sgr A* shows very unique and various phenomena mostly originated from young stellar populations. We report on the X-ray perspective on the young stellar populations which are related to our Galactic Center activities. The discussion is essentially based on the observational facts of new X-ray objects in the Galactic Center region in the $1^\circ \times 2^\circ $ area. They are; Clusters of young high mass stars, which are Sgr B2, Arches, IRS 13 and Quintuplet. X-ray reflections in the giant molecular clouds, such as Sgr B2, Sgr C, M0.01-0.09 and others. New candidates of X-ray supernova remnants (SNRs), which are Sgr A East, G0.570-0.018 and G359.8-0.3. Non-thermal Jets, Filaments and Shells, which are unique X-ray features in the GC region. These X-ray features may be closely related with each other, hence may have common origins. A unified picture is presented for the X-ray activity of our Galactic Center comparing with the X-ray spectra from other type of galaxies such as; Star burst galaxy (NGC 253), low luminosity AGN (M 81) and Seyfert 2 (NGC 1068).

New X-ray Telescope (NeXT) will be the next Japanese X-ray astronomical satellite, which will be launched around 2010. A multilayer super mirror will give NeXT a large effective area across the 0.1–80 keV band. This wide bandpass requires a focal plane detector that is also sensitive along the entire energy band. As the focal plane detector for NeXT, we have been developing a Wideband hybrid X-ray Imager (WXI) consisting of X-ray CCDs and pixelized CdTe detector. The X-ray CCD of the WXI is required to maintain high quantum efficiency up to the high-energy band while allowing hard X-rays to pass undetected through the depletion (sensitive) layer. In order to meet these requirements, we have been developing a back supportless CCD (BS-CCD) which has a thick depletion layer, a thinned Si wafer and a back supportless structure. As the first step, we manufactured a test model of BS-CCD in order to (1) learn the handling and thinning process and (2) confirm that there is no change of the performance. For the mechanical strength and the safe handling of the wafer, we decided to thin the wafer to ∼ 200 μ m . We verified the thickness of the depletion layer and wafer of the BS-CCD to be about 70 and 190 μ m , respectively. The energy resolution at 5.9 keV of 144 eV and the read-out noise of 7 electrons (rms) are equal to those of an un-thinned CCD, hence, we confirmed that our thinning process has no effect on the performance.

著者人数: 13名, 資料番号: SA1004001000

We report measurements by Chandra of a variety of X-ray sources in the molecular clouds and HII regions of the Sgr B2, Arches, Quintuplet and the Galactic center clusters. Moderately bright X-ray sources are present in the Sgr B2, Quintuplet and the Galactic center clusters at the positions of ultra compact HII regions and bright infrared sources. Their X-ray spectra are fitted with models of a thin thermal plasma with 2–10 keV temperatures and luminosities of ∼1032–33erg s−1. The X-ray properties are typical of those of high-mass young stellar objects or clusters of such objects. The Arches Cluster has three bright X-ray sources, at the positions of bright IR and radio stars, with X-ray luminosities of a few ×1033 erg s−1 each, which may indicate an unusual X-ray emission mechanism from high mass YSOs. A unique X-ray feature of molecular clouds and HII regions near the Galactic center is the presence of diffuse emission with a strong 6.4 keV line; in Sgr B2 this is attributable to the fluorescence of gas irradiated by external sources in the Galactic center, while the diffuse emission from Arches is puzzling.

We report on the results of the Chandra observation on the central region of the Monoceros R2 cloud (Mon R2), a high-mass star-forming region (SFR). With a deep exposure of 100 ks, we detected 368 X-ray sources, 80% of which were identified with the NIR counterparts. We systematically analyzed the spectra and time variability of most of the X-ray emitting sources and provided a comprehensive X-ray source catalog for the first time. Using the J-, H-, and K-band magnitudes of the NIR counterparts, we estimated the evolutionary phase (classical T Tauri stars and weak-lined T Tauri stars) and the mass of the X-ray emitting sources, and analyzed the X-ray properties as a function of the age and mass. We found a marginal hint that classical T Tauri stars have a slightly higher temperature (2.4 keV) than that of weak-lined T Tauri stars (2.0 keV). A significant fraction of the high- and intermediate-mass sources have a time variability and high plasma temperatures (2.7 keV). We performed the same analysis for other SFRs, the Orion Nebula Cluster and Orion Molecular Cloud-2/3, and obtained similar results to Mon R2. This supports the earlier results of this observation obtained by Kohno et al. (2002, ApJ, 567, 423) and Preibisch et al. (2002, A&A, 392, 945) that high- and intermediate- mass young stellar objects emit X-rays via magnetic activity. We also found a significant difference in the spatial distribution between X-ray and NIR sources., 21 pages, 7 figures, accepted for publication in PASJ, the complete version with figures and tables is available at ftp://ftp-cr.scphys.kyoto-u.ac.jp/pub/crmember/nakajima/MonR2.ps.gz

We propose a new type of wide band X-ray imaging spectrometer as a focal plane detector of the super mirror onboard on future X-ray missions including post Astro-E2. This camera is realized by the hybrid of back illumination CCDs and a back supportless CCD for 0.05–10 keV band, and a Micro Pixel Gas Chamber detecting X-rays at 10–80 keV.

We report on the development of the X-ray CCD for the soft X-ray imager (SXI) onboard ASTRO-H. SXI CCDs are P-channel, back-illuminated type manufactured by Hamamatsu Photonics K. K. Experiments with prototype CCD for the SXI shows the device has a depletion layer as thick as 200μm, high efficiency for hard X-rays. By irradiating soft X-rays to the prototype CCD for the SXI. At the same time, we found a significant low energy tail in the soft X-ray response of the SXI prototype CCD. We thus made several small size CCD chips with different treatment in processing the surface layers. CCDs with one of the surface layers treatment show a low energy tail of which intensity is one order of magnitude smaller than that of the original SXI prototype CCD for 0.5keV X-ray incidence. The same treatment will be applied to the flight model CCDs of the SXI. We also performed experiments to inject charge with the SXI prototype CCD, which is needed to mitigate the radiation damage in the orbit. We investigated the operation conditions of the charge injection. Using the potential equilibration method, charges are injected in each column homogeneously, though the amount of the charge must be larger than 20ke-.

NeXT (New X-ray Telescope) is the next Japanese X-ray astronomical satellite mission after the Suzaku satellite. NeXT aims to perform wide band imaging spectroscopy. Due to the successful development of a multilayer coated mirror, called a supermirror, NeXT can focus X-rays in the energy range from 0.1 keV up to 80 keV. To cover this wide energy range, we are in the process of developing a hybrid X-ray camera, Wideband X-ray Imager (WXI) as a focal plane detector of the supermirror. The WXI consists of X-ray CCDs (SXI) and CdTe pixelized detectors (HXI), which cover the lower and higher X-ray energy bands of 0.1-80 keV, respectively. The X-ray CCDs of the SXI are stacked above the CdTe pixelized detectors of the HXI. The X-ray CCDs of the SXI detect soft X-rays below $\sim$ 10 keV and allow hard X-rays pass into the CdTe detectors of the HXI without loss. Thus, we have been developing a "back-supportless CCD" with a thick depletion layer, a thinned silicon wafer, and a back-supportless structure. In this paper, we report the development and performances of an evaluation model of CCD for the SXI, "CCD-NeXT1". We successfully fabricated two types of CCD-NeXT1, unthinned CCDs with 625-um thick wafer and 150-um thick thinned CCDs. By omitting the polishing process when making the thinned CCDs, we confirmed that the polishing process does not impact the X-ray performance. In addition, we did not find significant differences in the X-ray performance between the two types of CCDs. The energy resolution and readout noise are $\sim$ 140 eV (FWHM) at 5.9 keV and $\sim$5 electrons (RMS), respectively. The estimated thickness of the depletion layer is $\sim$80 um. The performances almost satisfy the requirements of the baseline plan of the SXI., Comment: 20 pages, 10 figures, Accepted for publication in NIMA

The next Japanese X-ray astronomical satellite mission, NeXT , was proposed to ISAS/JAXA following the Astro-E2 Suzaku satellite which was launched in July 2005. We develop an X-ray CCD camera system, SXI (Soft X-ray Imager), for NeXT . The Hard X-ray Telescope (HXT) onboard NeXT provides imaging capability up to 80 keV, using the multilayer-coated X-ray mirror technology, called "Supermirror", newly developed in Japan. SXI is one of the focal plane detectors of HXT, which covers the soft energy band in the 0.5-12 keV in the baseline and 0.3-25 keV in the goal. We develop p-type CCDs for the baseline of SXI because p-type CCDs have been successfully used for previous X-ray astronomical satellites. We developed a prototype of a p-type CCD for SXI, called "CCD-NeXT1". CCD-NeXT1 is a frame-transfer CCD with two readout nodes. The image area of CCD-NeXT1 consists of 2Kx2K pixels with a pixel size of 12 μm x 12 μm. We evaluated performance of CCD-NeXT1 devices, KG-4 and KG-5. The energy resolution was 141.8±0.6 eV full width at half maximum at 5.9 keV, the readout noise was 4.7±0.2 e-, the horizontal CTI was < 5.1 x 10-7, and the vertical CTI was < 2.4 x 10-7 for KG-5. The performance of KG-4 was more or less the same as that of KG-5. The thickness of the depletion layer was 82±7 μm for KG-4 and 76±6 μm for KG-5. We conclude that our technology for p-type CCDs is sufficient to satisfy the CCD performance for the baseline of SXI.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We give overview and the current status of the development of the Soft X-ray Imager (SXI) onboard the NeXT satellite. SXI is an X-ray CCD camera placed at the focal plane detector of the Soft X-ray Telescopes for Imaging (SXT-I) onboard NeXT. The pixel size and the format of the CCD is 24 x 24μm (IA) and 2048 x 2048 x 2 (IA+FS). Currently, we have been developing two types of CCD as candidates for SXI, in parallel. The one is front illumination type CCD with moderate thickness of the depletion layer (70 ~ 100μm) as a baseline plan. The other one is the goal plan, in which we develop back illumination type CCD with a thick depletion layer (200 ~ 300μm). For the baseline plan, we successfully developed the proto model 'CCD-NeXT1' with the pixel size of 12μm x 12μm and the CCD size of 24mm x 48mm. The depletion layer of the CCD has reached 75 ~ 85μm. The goal plan is realized by introduction of a new type of CCD 'P-channel CCD', which collects holes in stead of electrons in the common 'N-channel CCD'. By processing a test model of P-channel CCD we have confirmed high quantum efficiency above 10 keV with an equivalent depletion layer of 300μm. A back illumination type of P-channel CCD with a depletion layer of 200μm with aluminum coating for optical blocking has been also successfully developed. We have been also developing a thermo-electric cooler (TEC) with the function of the mechanically support of the CCD wafer without standoff insulators, for the purpose of the reduction of thermal input to the CCD through the standoff insulators. We have been considering the sensor housing and the onboard electronics for the CCD clocking, readout and digital processing of the frame date.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have been developing fully-depleted CCDs fabricated on N-type silicon wafer in collaboration with HAMAMATSU Photonics K.K.We have made several wafer runs to optimize the basic characteristics of the devices such as the charge transfer efficiency (CTE), the full-well capacity and the amplifier gain, followed by the optimization of the backside treatment to improve quantum efficiency (QE) in blue wavelengths. The optimization process is successfully completed, and Hamamatsu recently started to deliver the 2k × 4k (15 μm pixel) four-side buttable devices for acceptance evaluation at the National Astronomical Observatory of Japan. Based on the measured QE in the X-ray, the depletion depth reaches 200 μm with CTE as good as >0.999995 for serial and parallel directions and with readout noise of < 5 e- for 130 kHz readout. The size of charge diffusion is estimated to be < 7.5 μm (one sigma) for pinhole image at wavelength of 450 nm. The device flatness is < 15-20 μm, and the dark current is a few e-/hour/pixel at -100°C and ~ 20 e-/hour/pixel at -80°C.

The NeXT (New X-ray Telescope) satellite to be launched around 2010, has a large effective area in the 0.1-80 keV band with the use of the multilayer super mirror (HXT). As one of the focal plane detectors for NeXT, we have been developing the Soft X-ray Imager (SXI). SXI consists of charge coupled devices (CCDs). In order to increase the quantum efficiency (Q.E.) as high as possible, i.e., to detect X-rays collected by HXT as many as possible, we developed a "fully-depleted and back-illuminated CCD" in the attempt to improve the Q.E. of soft X-rays by the back-illuminated structure and that of hard X-rays by thickening of a depletion layer. Thanks to a high-resistivity (over 10kΩ•cm) n-type Si, we have successfully developed Pch CCDs with very thick depletion layer of over 300 micron, which is 4 times thicker than that of established X-ray MOS CCDs (for example XIS, EPIC-MOS and ACIS-I). Furthermore, we have already confirmed we can thin a wafer down to 150 micron independent of its resistivity from the experience of the development of the back supportless CCD. Based on these successful results, we fabricated a test device of "fully depleted and back-illuminated CCD" with the high resistivity (10kOhm cm) N-type Si thinned down to 200 micron. The pixel number and size are 512 x 512 and 24 x 24 μm, respectively. For optical blocking, we coated the surface with Al. We evaluated this test device and confirmed the thickness of depletion layer reaches 200 micron as we expected. In this paper, we present progress in development of these devices for SXI.

The NeXT (New X-ray Telescope) satellite to be launched around 2010, has a large effective area in the 0.1-80 keV band with the use of the multilayer super mirror. As the focal plane detector for NeXT , we have been developing the Wideband hybrid X-ray Imager (WXI) consisting of X-ray CCDs and a hard X-ray imager placed under X-ray CCDs. The X-ray CCD of WXI is required to (1) keep the high quantum efficiency up to the high energy band and (2) pass hard X-rays unabsorbed in the depletion (sensitive) layer. In order to meet these requirements, we have been developing the back supportless CCD which has the thick depletion layer, thinned Si wafer and back supportless structure. As the first step, we make the test model with thinned Si wafer in order to (1) learn the handling and thinning process and (2) confirm no change of the performance after the thinning process. The test model has the pixel number and size of 512 x 512 and 24 x 24 μm, respectively. We select the thickness of the wafer is about 200 μm considering the thinning process. We verify the depletion layer and the wafer of the test model are about 65 and 190 μm in thickness, respectively. The energy resolution is about 144 eV at 5.9 keV which is substantially comparable to the un-thinned CCD, hence we confirm our thinning process has no effect on the perfomance. In order to reduce the dead layer ompletely and increase the quantum efficiency at the high energy band, we are also developing the full depleted X-ray CCD with the high resistivity N-type Si wafer.

Quantum Efficiency (QE) of CCDs decreases at λ >~ 0.7 μm since photons penetrate a depletion layer of CCD. If one makes the layer thicker, the QE will be largely improved. In collaboration with HAMAMATSU Photonics, we have been developing the thicker CCDs which are implemented on the high resistivity n-type silicon wafers. We have made several wafer runs to optimize the basic characteristics of the devices such as charge transfer efficiency (CTE), full-well and node sensitivities of the amplifiers. The results obtained so far mostly satisfied the specifications imposed by astronomical observations. We also attempted to build back-side illuminated devices to realize high QE in wider wavelength. The test devices shows that the QE exceeds 60% at 1 μm, which is roughly 5 ~ 6 times improvement over ordinary CCDs. We will present the current status of the projects.

We report on a peculiar X-ray binary pulsar IKT1 = RXJ0047.3-7312 observed with XMM-Newton in Oct. 2000. The X-ray spectrum is described by a two-component spectrum. The hard component has a broken power-law with respective photon indices of 0.2 and 1.8, below and above the break energy at 5.8 keV. The soft component can be modeled by a blackbody of kT = 0.6 keV. The X-ray flux shows a gradual decrease and periodic variations of about 4000 s. The averaged flux in 0.7-10.0 keV is 2.9x10^-12 ergs/cm^2/s, which is ~10 times brighter than that in a ROSAT observation in Nov. 1999. In addition to the 4000-s variation, we found coherent pulsations of 263 +/- 1 s. These discoveries strengthen the Be/X-ray binary scenario proposed by the ROSAT and ASCA observations on this source, and confirm that most of the hard sources in the Small Magellanic Cloud are X-ray binary pulsars. A peculiar property of this XBP is that the coherent pulsations are found only in the soft component, and the folded light curve shows a flat top shape with a sharp dip. We discuss the nature of this XBP focusing on the peculiar soft component., 5 pages, 5figures, Accepted for publication in PASJ

We are developing an X-ray charge-coupled device (CCD) for the next Japanese X-ray astronomical satellite mission, NeXT (New X-ray Telescope/Nonthermal energy eXploration Telescope). We developed a trial product of the p-channel CCD fabricated on an n-type silicon wafer. It is possible to have a thick depletion layer of ∼300 µm with a p-channel CCD because it is easy to obtain high resistivity using an n-type silicon wafer compared with a p-type silicon wafer. We evaluated the performance of the p-channel CCD. The imaging area of the CCD consists of 512×512 pixels with a pixel size of 24×24 µm2. The horizontal charge transfer inefficiency (CTI) of the CCD can be improved by reducing the operating temperature and increasing the readout frequency. We obtained the best horizontal CTI of (0.98±0.09)×10-5 with an energy resolution of (202±6) eV full width at half maximum (FWHM) for 5.9 keV X-rays and a readout noise of 18 e- (rms) when the CCD was operated at a temperature of -110 °C and a readout frequency of 67 kHz. We measured the thickness of the depletion layer to be (290±33) µm from the detection efficiency of the 22.4 and 24.9 keV emission lines from 109Cd.