We report MAXI and Swift observations of short-term spectral softenings of the Galactic black hole X-ray binary Swift J1753.5−0127 in the low/hard state. These softening events are characterized by a simultaneous increase of soft X-rays (2–4 keV) and a decrease of hard X-rays (15–50 keV) lasting for a few tens of days. The X-ray energy spectra during the softening periods can be reproduced with a model consisting of a multi-color disk blackbody and its Comptonized component. The fraction of the Comptonized component decreased from 0.30 to 0.15 when the spectrum became softer; meanwhile the inner disk temperature (Tin) increased from 0.2 to 0.45 keV. These results imply that the softening events are triggered by a short-term increase of the mass accretion rate. During the observed spectral softening events, the disk flux (Fdisk) and Tin did not obey the Fdisk ∝ (Tin )4 relation, suggesting that the inner disk radius does not reach the innermost stable circular orbit.
Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ; HAp) is one of inorganic components of bone and teeth, and has an osteoconductivity and execellent biocompatibility. Thus, the HAp has been used as biomaterials for bone graftings. Clinically-used HAp cements are set on the basis of the acid-base reaction of Ca 4 O(PO 4 ) 2 and CaHPO 4 . This mechanism accompany the changes of pH during hardening, leading to inflammation around tissues, together with slow setting time. We have succeeded to develop novel HAp cement, which is created by mixing the HAp powder modified with inositol phosphate (IP6) and water. The present IP6-HAp cement is set based on the chelate-bonding of IP6 without the acid-base reaction. The IP6 is not only biocompatible but also has able to chelate to some metal ions as strongly as EDTA. In the present study, we fabricated four kinds of IP6-HAp cements using commercially-available HAp powders with diferent morphology and specific surface area (SSA): HAp-100 (fine particle), HAp-200 (hexagonal shape), HAp-400 (plate shape), and s-HAp (spherical shape). Among the cement specimens examined, the IP6/HAp-100 cement derived from HAp-100 powder had maximum compressive strength of 10 MPa under following condition: Powder/Liquid (P/L) ratio=1/0.45[w/w]. The HAp-100 powder was composed of microcrystals with the highest SSA of 62.4 m 2 ・g -1 among the HAp powder used in the present work. On the other hand, the compressive strength of the IP6/HAp-200 cements showed the lowest value of 2 MPa under following condition: P/L ratio=1/0.35[w/w]. The HAp-200 powder of a starting material was composed of hexagonal-shaped crystals, and had the lowest SSA of 7.0 m 2 ・g -1 . These results indicate that the compressive strength of novel IP6/HAp cements was affected by powder properties, especially, the morphology and SSA of starting HAp powders.
We present observations of a transient He-like Fe K α absorption line in Suzaku observations of the black hole binary Cygnus X-1 on 2011 October 5 near superior conjunction during the high/soft state, which enable us to map the full evolution from the start and the end of the episodic accretion phenomena or dips for the first time.We model the X-ray spectra during the event and trace their evolution. The absorption line is rather weak in the first half of the observation, but instantly deepens for ∼10 ks, and weakens thereafter. The overall change in equivalent width is a factor of ∼ 3, peaking at an orbital phase of ∼ 0.08. This is evidence that the companion stellar wind feeding the black hole is clumpy. By analyzing the line with a Voigt profile, it is found to be consistent with a slightly redshifted Fe XXV transition, or possibly a mixture of several species less ionized than Fe XXV . The data may be explained by a clump located at a distance of ∼ 10 10−12 cm with a density of ∼ 10 (−13)−(−11) g cm −3 , which accretes onto and/or transits the line-of-sight to the black hole, causing an instant decrease in the observed degree of the ionization and/or an increase in density of the accreting matter. Continued monitoring for individual events with future X-ray calorimeter missions such as ASTRO-H and AXSIO will allow us to map out the accretion environment in detail and how it changes between the various accretion states.
Polarimetry is a powerful tool for astrophysical observations that has yet to be exploited in the X-ray band. For satellite-borne and sounding rocket experiments, we have developed a photoelectric gas polarimeter to measure X-ray polarization in the 2-10 keV range utilizing a time projection chamber (TPC) and advanced micro-pattern gas electron multiplier (GEM) techniques. We carried out performance verification of a flight equivalent unit (1/4 model) which was planned to be launched on the NASA Gravity and Extreme Magnetism Small Explorer (GEMS) satellite. The test was performed at Brookhaven National Laboratory, National Synchrotron Light Source (NSLS) facility in April 2013. The polarimeter was irradiated with linearly-polarized monochromatic X-rays between 2.3 and 10.0 keV and scanned with a collimated beam at 5 different detector positions. After a systematic investigation of the detector response, a modulation factor ≥35% above 4 keV was obtained with the expected polarization angle. At energies below 4 keV where the photoelectron track becomes short, diffusion in the region between the GEM and readout strips leaves an asymmetric photoelectron image. A correction method retrieves an expected modulation angle, and the expected modulation factor, ∼20% at 2.7 keV. Folding the measured values of modulation through an instrument model gives sensitivity, parameterized by minimum detectable polarization (MDP), nearly identical to that assumed at the preliminary design review (PDR).
The scientific objective of the X-ray Advanced Concepts Testbed (XACT) is to measure the X-ray polarization properties of the Crab Nebula, the Crab pulsar, and the accreting binary Her X-1. Polarimetry is a powerful tool for astrophysical investigation that has yet to be exploited in the X-ray band, where it promises unique insights into neutron stars, black holes, and other extreme-physics environments. With powerful new enabling technologies, XACT will demonstrate X-ray polarimetry as a practical and flight-ready astronomical technique. Additional technologies that XACT will bring to flight readiness will also provide new X-ray optics and calibration capabilities for NASA missions that pursue space-based X-ray spectroscopy, timing, and photometry.
We successfully produced Resistive-Electrode Gas Electron Multiplier (RE-GEM) which has resistive electrodes instead of the metal ones which are employed for the standard GEM foils. RE-GEM has a resistive electrode of 25 µm-thick and an insulator layer of 100 µm-thick. The hole structure of RE-GEM is a single conical with the wider and narrower hole diameters of 80 µm and 60 µm, respectively. A hole pitch of RE-GEM is 140 µm. We obtained the maximum gain of about 600 and the typical energy resolution of about 20% (FWHM) at an applied voltage between the resistive electrodes of 620 V, using a collimated 8 keV X-rays from a generator in a gas mixture of 70% Ar and 30% CO 2 by volume at the atmospheric pressure. We measured the effective gain as a function of the electric field of the drift region and obtained the maximum gain at an drift field of 0.5 kV/cm.
We have performed a systematic investigation of the gain properties of the GEM foil made from copper-clad liquid crystal polymer insulator (LCP-GEM), which will be used for a satellite mission. We have measured the gain curve of LCP-GEM in pure DME at 190 Torr, and achieved a gain of 3×10 4 at an applied high voltage of 605 V between the LCP-GEM electrodes with a thickness of 100 µm. The charge sharing between the GEM electrodes and readout pad were measured as a function of drift (E d ) or induction (E i ) field. We found that the parallel plate multiplication occurred between the bottom electrode of LCP-GEM and the readout pad above E i = 6 kV/cm, and the amount of charge collected in each electrode was almost constant with E d . We investigated the signal shape obtained in each electrode and found that the rise time of signals was explained as induced charge by moving ions and electrons.
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