Yoshiki Kohmura

The nature of ultraluminous compact X-ray sources in nearby spiral galaxies

Studies were made of ASCA spectra of seven ultraluminous compact X-ray sources in nearby spiral galaxies: M33 X-8, M81 X-6, IC 342 source 1, Dwingeloo 1 X-1, NGC 1313 source B, and two sources in NGC 4565. With the 0.5-10 keV luminosities in the range 1039-1040 ergs s-1, they are thought to represent a class of enigmatic X-ray sources often found in spiral galaxies. For some of them, the ASCA data are newly processed or the published spectra are reanalyzed. For others, the published results are quoted. The ASCA spectra of all seven sources have been described successfully with so-called multicolor disk blackbody emission arising from optically thick standard accretion disks around black holes. Except for the case of M33 X-8, the spectra do not exhibit hard tails. For the source luminosities not to exceed the Eddington limits, the black holes are inferred to have rather high masses, up to ~100 M☉. However, the observed innermost disk temperatures of these objects, Tin = 1.1-1.8 keV, are too high to be compatible with the required high black hole masses, as long as the standard accretion disks around Schwarzschild black holes are assumed. Similarly high disk temperatures are also observed from two Galactic transients with superluminal motions, GRO 1655-40 and GRS 1915+105. The issue of unusually high disk temperature may be explained by the black hole rotation, which makes the disk get closer to the black hole and hence hotter.

Macromolecular structures probed by combining single-shot free-electron laser diffraction with synchrotron coherent X-ray imaging

Nanostructures formed from biological macromolecular complexes utilizing the self-assembly properties of smaller building blocks such as DNA and RNA hold promise for many applications, including sensing and drug delivery. New tools are required for their structural characterization. Intense, femtosecond X-ray pulses from X-ray free-electron lasers enable single-shot imaging allowing for instantaneous views of nanostructures at ambient temperatures. When combined judiciously with synchrotron X-rays of a complimentary nature, suitable for observing steady-state features, it is possible to perform ab initio structural investigation. Here we demonstrate a successful combination of femtosecond X-ray single-shot diffraction with an X-ray free-electron laser and coherent diffraction imaging with synchrotron X-rays to provide an insight into the nanostructure formation of a biological macromolecular complex: RNA interference microsponges. This newly introduced multimodal analysis with coherent X-rays can be applied to unveil nano-scale structural motifs from functional nanomaterials or biological nanocomplexes, without requiring a priori knowledge.

X-RAY FOCUSING TEST AND X-RAY IMAGING TEST BY A MICROCAPILLARY X-RAY LENS AT AN UNDULATOR BEAMLINE

A first focusing test of the undulator radiation at SPring-8 has been done using two types of x-ray refractive lenses in thin glass capillaries. One (lens No. 1) contained bubbles in a glue whereas the other (lens No. 2) contained bubbles in glycerol. The capillaries had inner diameters of 0.2 and 0.8 mm, respectively. Using x rays of 17–18 keV, the undulator source image was investigated at the focal plane. The spherical aberrations and the field distortions were carefully examined by taking the images of a gold mesh. Lens No. 1 had an advantage of high transmissivity in the hard x-ray region (18% at 18 keV) and high tolerance to severe radiation damage, e.g., ∼5×1012 photons/s/0.03 mm2 of the 18 keV x rays for an exposure time of 1 h. On the other hand, lens No. 2 had an advantage of a large aperture, 0.8 mm, and a small field distortion, e.g., less than 10% inside a diameter of 300 μm.

KOTOBUKI-1 apparatus for cryogenic coherent X-ray diffraction imaging

We have developed an experimental apparatus named KOTOBUKI-1 for use in coherent X-ray diffraction imaging experiments of frozen-hydrated non-crystalline particles at cryogenic temperature. For cryogenic specimen stage with small positional fluctuation for a long exposure time of more than several minutes, we here use a cryogenic pot cooled by the evaporation cooling effect for liquid nitrogen. In addition, a loading device is developed to bring specimens stored in liquid nitrogen to the specimen stage in vacuum. The apparatus allows diffraction data collection for frozen-hydrated specimens at 66 K with a positional fluctuation of less than 0.4 μm and provides an experimental environment to easily exchange specimens from liquid nitrogen storage to the specimen stage. The apparatus was developed and utilized in diffraction data collection of non-crystalline particles with dimensions of μm from material and biological sciences, such as metal colloid particles and chloroplast, at BL29XU of SPring-8. Recently, it has been applied for single-shot diffraction data collection of non-crystalline particles with dimensions of sub-μm using X-ray free electron laser at BL3 of SACLA.

X‐ray optics research and development for SPring‐8 beamlines

X‐ray optics research and development for SPring‐8 beamlines are described. These include standard developments of monochromators, high‐heat load optics, wide energy‐range monochromators for bending beamlines, long x‐ray mirrors, and single and graded d‐spacing synthetic multilayers.

Wavefront measurement for a hard-X-ray nanobeam using single-grating interferometry

Wavefront measurement for a hard-X-ray nanobeam using single-grating interferometry based on the Talbot effect and the Fourier transform method was demonstrated in the 1-km-long beamline of SPring-8. 10 keV X-rays were one-dimensionally focused down to 32 nm using a total-reflection elliptical mirror. An intentionally distorted wavefront was generated using a deformable mirror placed just upstream of the focusing mirror. The wavefront measured by interferometry was cross-checked with the phase retrieval method using intensity profiles around the beam waist. Comparison of the obtained wavefront errors revealed that they are in good agreement with each other and with the wavefront error estimated from the shape of the deformable mirror at a ~0.5 rad level.

Hard-X-ray imaging optics based on four aspherical mirrors with 50 nm resolution

Ultraprecise imaging optics, which consists of two sets of elliptical mirrors and hyperbolic mirrors aligned perpendicular to each other (i.e., advanced Kirkpatrick-Baez mirrrors), is developed to realize high-resolution and achromatic full-field hard-X-ray microscopy. Experiments to form a demagnified image (with horizontal and vertical demagnification factors of 385 and 210, respectively) are conducted to evaluate the optical system at an X-ray energy of 11.5 keV at SPring-8. Results show that the imaging system can form a demagnified image with nearly diffraction-limited resolutions of ~50 nm in the horizontal and vertical directions. The field of view is also experimentally estimated to be ~12 × ~14 μm(2) when used as a magnification imaging system.

Multiscale element mapping of buried structures by ptychographic x-ray diffraction microscopy using anomalous scattering

We propose an element mapping technique of nano-meso-microscale structures buried within large and/or thick objects by ptychographic x-ray diffraction microscopy using anomalous scattering. We performed quantitative imagings of both the electron density and Au element of Au/Ag nanoparticles at the pixel resolution of better than 10 nm in a field of view larger than 5 × 5 μm2 by directly phasing ptychographic coherent diffraction patterns acquired at two x-ray energies below the Au L3 edge. This method provides us with multiscale structural and elemental information for understanding the element/property relationship linking nanoscale structures to macroscopic functional properties in material and biological systems.

High-resolution and high-sensitivity phase-contrast imaging by focused hard x-ray ptychography with a spatial filter

We demonstrate high-resolution and high-sensitivity x-ray phase-contrast imaging of a weakly scattering extended object by scanning coherent diffractive imaging, i.e., ptychography, using a focused x-ray beam with a spatial filter. We develop the x-ray illumination optics installed with the spatial filter to collect coherent diffraction patterns with a high signal-to-noise ratio. We quantitatively visualize the object with a slight phase shift (∼λ/320) at spatial resolution better than 17 nm in a field of view larger than ∼2×2μm2. The present coherent method has a marked potential for high-resolution and wide-field-of-view observation of weakly scattering objects such as biological soft tissues.

X-Ray Spectrum of Supernova 1993J Observed with ASCA and Its Evolution 8-572 Days after the Explosion

ASCA observations of the supernova in M81, SN 1993J, 8-572 days after the explosion are presented. Utilizing a one-dimensional image-fitting to the Solid-State Imaging Spectrometer (SIS) data, energy spectra of the supernova in 0.5-8 keV are obtained. The spectrum showed drastic softening with a power-law photon index of 0.3-4, while the X-ray intensity decreased from 0.03 to 0.008 counts s-1 SIS-1. The early phase of spectra requires two thermal emission components of different absorption columns if they are fitted with thermal models. The temperatures of two emission components cannot be well constrained with ASCA continuum spectra. However, the detection of an iron K emission line with ASCA and the hard X-ray spectra observed by OSSE on the Compton Gamma-Ray Observatory suggest that the two components have different temperatures: a few keV and about 100 keV. The properties of the two emission components are consistent with emissions from the front and reverse shocks of the supernova explosion. The drastic softening of the X-ray spectra is explained by the decrease of the absorption column density of the reverse shock component and the change of the major contributor to the soft X-ray band from the front to the reverse shocks.