Shunji Kitamoto

A new X-ray pulsar GS 2138 + 56 (Cepheus X-4)

A transient X-ray pulsar was discovered with the Ginga satellite at the position of alpha(1950) = 21 h 38 m + or - 1 m, delta(1950) = 56 deg 50 arcmin + or - 6 arcmin (designed as GS 2138 + 56). The error box includes the previously reported transient source Cep X-4. An X-ray pulsation with a heliocentric pulse period of 66.2490 + or - 0.0001 sec (at MJD = 47263.5) was discovered. Assuming no intrinsic change of the pulse period during the observation, a lower limit of the orbital period of 23 days and projected semiaxis of 9 lt-sec are obtained. The X-ray spectrum has a typical shape for X-ray pulsars having power-law index of about 1.0 with an exponential cutoff at an energy typical shape for X-ray pulsars having power-law index of about 1.0 with an exponential cutoff at an energy of about 16 keV. It is suggested, based on circumstantial evidence, that GS 2138 + 56 is likely to be Be star binary. 13 refs.

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.

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.

Suzaku observations of six early type stars

We investigate spectra of six early type stars, four stars in Cyg OB2 association (Nos. 5, 8a, 9 and 12), ζ Oph and τ Sco, observed with Suzaku. Statistically good Suzaku-data provide us a unique tool for comparing their global spectral shape in X-ray band. We found that three Cyg OB2 stars, Nos. 5, 8a and 12, show similar high-energy-spectral shape to that of τ Sco, with high temperature (~1.5 keV) component. On the other hand, we found that ζ Oph shows a lack of the high energy component comparing to the other stars.

A self charge filling (SCF) effect of Suzaku-XIS

In general, the charge transfer efficiency (CTE) of CCD gradually degrades due to multiplication of charge traps made by cosmic-rays. The Suzaku-XIS is also suffered this degradation. In order to restore it, the spaced-row charge injection (SCI) has been used since October 2006, where injected charges fill the traps and charges of interesting are not trapped. A similar effect should happen during observation of bright sources. Around the image center of a bright source, we can find several pixels filled by charges in a certain raw. Since the leading pixel fills a trap, the following pixels do not suffer the charge trapping. Thus we can expect same effect to that of the SCI, and we call this a Self Charge Filling (SCF) effect. We propose a correction method of the SCF effect and show its validity by applying it for extraction of the spectra of Cygnus X-3.