Noriko Y. Yamasaki

Newly developed low background hard X-ray/gamma-ray telescope with the well-type phoswich counters

A low background hard X-ray/gamma-ray telescope (Welcome-1) for balloon-borne experiments in the energy range from 40 keV to 800-1000 keV is discussed. The detector is based on newly developed well-type phoswich counters. In the first well-type phoswich counter, GSO(Ce) (Gd/sub 2/SiO/sub 5/ doped with Ce) is used as the detection part and CsI(Tl) as the shielding part. Welcome-1 consists of 64 GSO/CsI well-type phoswich counters assembled in the compound-eye configuration, and the effective area is 740 cm/sup 2/ at 122 keV and 222 cm/sup 2/ at 511 keV line. The well-type phoswich counter and the compound eye configuration reduce background significantly both externally and internally, and allow a high signal-to-noise ratio in balloon-borne experiments. The background levels at an attitude of 4.5 g/cm/sup 2/ are 1*10/sup -4//cm/sup 2//s/keV at 122 keV. Crab nebula is observed with the signal to background ratio better than unity between 100 and 200 keV. The design of the telescope and the flight performance are presented. >

Transmission measurement of the spare Beryllium window of the SXS onboard the Hitomi satellite in 2.0-12 keV with KEK-PF

The Soft X-ray Spectrometer (SXS) onboard the Hitomi (ASTRO-H) satellite observed several celestial objects. All the observations with the SXS were performed through a beryllium (Be) window installed on the gate-valve of the SXS dewar. However, the Be window had not been well calibrated before launching. Therefore, we measured the transmission of a spare Be window, which is from the same lot as the flight material. The measurements were preformed in 3.8–30 keV range with BL01B1 at SPring-8, and in 2.5–12 keV range combined with BL11B and BL7C at KEK-PF. In this paper, we report mainly the results of the KEK-PF experiment. With the KEK-PF, we measured five places of the Be window. Their estimated thicknesses are consistent with each other within 1.3 μm. In the five transmission data, we confirmed absorption edges by Fe-K, Ni-K and Mn-K and six edge like features at 3460, 6057, 6915, 7590, 8790 and 9193 eV, which can be interpreted as Bragg diffraction by Be polycrystal. By combining the transmissions measured at KEK-PF and at SPring-8, we estimated Be thickness of 259.73±0.01 μm. The amounts of contaminated materials are roughly comparable with the provided values from the provider. We also performed scanning measurements of whole surface in the Be window. In the results, thickness of Be window was found to be uniform in ±1µm from the measurement with 4 keV X-rays.

New hard X-ray/gamma-ray telescope - Welcome-1

We have developed a low background hard X-ray/gamma-ray telescope for balloon-borne experiments. The telescope called Welcome-1 (Well type Compound Eye) utilizes newly developed well-type phoswich counters. In the well-type phoswich counter, the background from external and internal sources are reduced significantly, Welcome-1 is designed for observation in the energy range from 60 keV to 800-1000 keV. The effective area of Welcome-1 is 740 sq cm at 122 keV and 222 sq cm at 511 keV line. We flew Welcome-1 in 1990 and 1991 to detect hard X-rays from SN1987A, PSR1509-58, Cen-A and others. The background levels at an altitude of 4g/sq cm are 1 x 10 exp -4/sq cm photons/s/keV at 122 keV and 3 x 10 exp -5 photons/sq cm/s/keV at 511 keV. The data obtained during the flight shows that the detector in fact has the 3 sigma sensitivity of about a few x 10 exp -6 photons/sq cm/s/keV and about 10 exp -4 photons/sq cm/s in a 10 exp 4 s observation for the continuum spectrum and line spectrum, respectively.

The evaluation of the Hitomi (Astro-H)/SXS spare beryllium window in 3.8-30 keV

During the Hitomi (Astro-H) commissioning observations the SXS dewar gate valve (GV) remained closed to protect the instrument from initial spacecraft outgassing. As a result, the optical path of the observations included the Be window installed on the GV. Both x-ray fluorescence (XRF) analysis and x-ray transmission measurements were performed in June 2016 on the flight-spare Be window which is the same lot as the flight material at SPring-8 in Japan. The beamline operating range is 3.8 - 30 keV. We used a beam spot size of 1 mm × 0.2 mm to measure two positions on the Be window, at the center of the window and at one position 6.5 mm off-center. We used simultaneous transmission measurements of standard materials for energy calibration. The transmission data clearly showed Fe and Ni K-edges, plus a marginal detection of the Mn K-edge. We found that our transmission data was best fit using the following component Be: 261.86±0.01μm, Cr: 3nm (fixed), Mn: 3.81±0.05nm, Fe: 10.83±0.05nm, Ni: 16.48±0.03nm, Cu: 5nm (fixed). The transmission is reduced 1% at the Fe K-edge. The amount of contaminated materials are comparable to the values of the value provided by the vender. The surface transmission is strained with σ = 0.11% of the unbiased standard deviation calculated variation in the residuals between the measured value and the model.

Hard x‐ray observation of Cen A and a break in the energy spectrum

We studied hard X‐ray/γ‐ray emission from Cen A (NGC 5128) in a balloon experiment with a low background detector (Welcome‐1) in Brazil. The energy spectrum of CenA is obtained from 40 keV to 600 keV. We combined the energy spectrum obtained by the Ginga satellite in a similar state. The combined spectrum indicates that there is a break at 185±22 keV. The spectrum is fitted to the broken power law model with the photon index of α1=−1.79 up to 188 keV, and α2=−3.7−1.7+0.9 above the break.

Super DIOS: future x-ray spectroscopic mission to search for dark baryons

We are working on an updated program of the future Japanese X-ray satellite mission DIOS (Diffuse Intergalactic Oxygen Surveyor), called Super DIOS. We keep the main aim of searching for dark baryons in the form of warmhot intergalactic medium (WHIM) with high-resolution X-ray spectroscopy. The mission will detect redshifted emission lines from OVII, OVIII and other ions, leading to an overall understanding of the physical nature and spatial distribution of dark baryons as a function of cosmological timescale. We are working on the conceptual design of the satellite and onboard instruments, with a provisional launch time in the early 2030s. The major changes will be improved angular resolution of the X-ray telescope and increased number of TES calorimeter pixels. Super DIOS will have a 10-arcsecond resolution and a few tens of thousand TES pixels. Most contaminating X-ray sources will be resolved, and the level of diffuse X-ray background will be reduced after subtraction of point sources. This will give us very high sensitivity to map out the WHIM in emission. The status of the spacecraft study will be presented: the development plan of TES calorimeters, on-board cooling system, X- ray telescope, and the satellite system. The previous study results for DIOS and technical achievements reached by the Hitomi (ASTRO-H) mission provide baseline technology for Super DIOS. We will also consider large scale international collaboration for all the on-board instruments.

Suzaku/XMM/Chandra study of Fe K line complex in the nuclear region of NGC 253

A bright, nearby edge-on starburst galaxy NGC 253 was studied using the Suzaku, XMM and Chandra X-ray observatories. Here, we focused on Suzaku and Chandra studies because of a good energy resolution with a low background and a sub-arcsecond spatial resolution. We detected with Suzaku complex line structure of Fe K, which is resolved into three lines (FeI at 6.4 keV, FeXXV at 6.7 keV and FeXXVI at 7.0 keV) around the center of NGC 253. Especially, the FeI and FeXXVI lines are the first clear detections, with a significance of >99.99% and 99.89% estimated by a Monte Carlo procedure. Imaging spectroscopy with Chandra revealed that the emission is distributed in ~60 arcsec2 region around the nucleus, which suggests that the source is not only the buried AGN.