Shin-ichiro Takagi

X-Ray Sources and Star Formation Activity in the Sagittarius B2 Cloud Observed with Chandra

We report the X-ray population study in the giant molecular cloud Sagittarius B2 (Sgr B2). More than a dozen X-ray cloud members (and candidates) are discovered with Chandra. Two bright X-ray sources are located near Sgr B2 Main, the most copious complex of the ultracompact H II sources. The X-ray spectra are fitted with a thin thermal plasma model of 5-10 keV temperature. The intrinsic luminosity, after correcting the absorption of ~5 × 1023 H cm-2, is ~1033 ergs s-1. Although these two X-ray sources are attributable to young stellar objects (YSOs) in the same H II complex, they are in sharp contrast; the one at the center of the H II complex exhibits strong K-shell transition lines of iron, while the other near the east has only weak lines. The other H II complexes, Sgr B2 North and South, also show hard and highly absorbed X-ray emissions due possibly to the star formation activity. The composite X-ray spectrum of the other cloud member X-ray sources is fitted with a thin thermal plasma of ~10 keV temperature with hydrogen column density (NH) of 1.3 × 1023 H cm-2 and individual X-ray luminosity of a few times 1031-1032 ergs s-1. These are likely to be a single YSO or cluster of YSOs, but neither radio nor infrared counterpart is found. An alternative scenario of isolated white dwarfs powered by Bondi-Hoyle accretion from the dense cloud gas is also discussed. The X-ray spectra exhibit an additional 6.4 keV line of neutral or low-ionization irons, which indicates that the environment gas is concentrated near the sources.

Recent results of the fully-depleted back-illuminated CCD developed by Hamamatsu

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.

Development of thick back-illuminated CCD to improve quantum efficiency in optical longer wavelength using high-resistivity n-type silicon

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.

X-Ray Observation on the Monoceros R2 Star-Forming Region with the Chandra ACIS-I Array

We report on the results of the Chandra ACIS-I observation on the central region of the Monoceros R2 cloud (Mon R2), a high-mass star-forming region (SFR) at a distance of 830pc. With a deep exposure of ∼ 100ks, we detected 368 X-ray sources, ∼80% of which were identified with the near-infrared (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 (2.4keV) than that of weak-lined T Tauri stars (2.0keV). A significant fraction of the high- and intermediate-mass sources have a time variability and high plasma temperatures (2.7keV) similar to those of low-mass sources (2.0keV). 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.

Development of p-Channel Charge-Coupled Device for NeXT, the Next Japanese X-ray Astronomical Satellite Mission

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.

Development of the x-ray CCD for SXI on board ASTRO-H

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-.

Development of p-type CCD for the NeXT: the next Japanese x-ray astronomical satellite mission

We have developed X-ray charge-coupled devices (CCD) for the next Japanese X-ray astronomical satellite mission, NeXT (Non-thermal energy eXploration Telescope). The hard X-ray telescope(HXT) onboard the NeXT can focus X-rays above 10 keV. Therefore, we need to develop an X-ray CCD for a focal plane detector to cover the 0.3-25 keV band in order to satisfy the capability of the telescope. We newly developed an n-type CCD fabricated on an n-type silicon wafer to expand the X-ray energy range as a focal plane detector of the HXT. It is possible to have a thick depletion layer of approx. 300μm with an n-type CCD because it is easy to obtain high resistivity with an n-type silicon wafer compared to a p-type silicon wafer. We developed prototypes of n-type CCDs and evaluated their X-ray performance, energy resolution, charge transfer inefficiency(CTI) and the thickness of the depletion layer of two devices, designated Pch15 and Pch-teg. We measured the thickness of the depletion layer of Pch15 to be 290±33μm. For Pch-teg, the energy resolution was 152±3eV full width at half maximum (FWHM) at 5.9 keV and the readout noise was 7.3 e-. The performance of the n-type CCDs was comparable to that of p-type CCDs, and their depletion layer were much thicker than those of p-type CCDs.

X-ray perspective on young stellar populations in objects with nuclear activity - the case of our Galactic Center-

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

Discovery of a Peculiar Pulsar in the Small Magellanic Cloud

1^\circ \times 2^\circ

The development of back-supportless CCDs and the wideband hybrid x-ray imager for the NeXT satellite

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).