Suzaku View of the Neutron Star in the Dipping Source 4U 1822−-37

The dipping X-ray source 4U 1822$-$37 was observed by Suzaku on 2006 Octrober 20 for a net exposure of 37 ks. The source was detected with the XIS at a 1-10 keV flux of 5.5$\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$, and with the HXD (HXD-PIN) at a 10-50 keV flux of 8.9$\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$. With HXD-PIN, the pulsation was detected at a barycentric period of 0.592437 s, and its change rate was reconfirmed as $-2.43\times$10$^{-12}$ s s$^{-1}$. The 1-50 keV spectra of 4U 1822-37 were found to be very similar to those of Her X-1 in the slopes, cutoff and iron lines. Three iron lines (Fe K$\alpha$, Fe XXV, and Fe XXVI) were detected, on top of a 1-50 keV continuum that is described by an NPEX model plus a soft blackbody. In addition, a cyclotron resonance scattering feature was detected significantly ($>99\%$ confidence), at an energy of 33$\pm$2 keV with a depth of 0.4$^{+0.6}_{-0.3}$. Therefore, the neutron star in this source is concluded to have a strong magnetic field of 2.8$\times10^{12}$ G. Further assuming that the source has a relatively high intrinsic luminosity of several times 10$^{37}$ erg s$^{-1}$, its spectral and timing properties are consistently explained

連星をなす強磁場中性子星の「すざく」衛星によるX線観測

学位の種別: 課程博士審査委員会委員 : (主査)東京大学准教授 山崎 典子, 東京大学教授 須藤 靖, 東京大学教授 駒宮 幸男, 東京大学教授 高田 昌広, 東京大学准教授 瀧田 正人University of Tokyo(東京大学

Spectral and Timing Nature of the Symbiotic X-ray Binary 4U 1954+319: The Slowest Rotating Neutron Star in an X-ray Binary System

The symbiotic X-ray binary 4U 1954+319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its ~5.4h NS spin period is the longest among all known accretion-powered pulsars and exhibited large (~7%) fluctuations over 8 years. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe Kalpha line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (~60-80%), and the location in the Corbet diagram favor high B-field (>~1e+12 G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (1e+33-1e+35 erg/s), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a ~1e+13 G NS, this scheme can explain the ~5.4 h equilibrium rotation without employing the magnetar-like field (~1e+16 G) required in the disk accretion case. The time-scales of multiple irregular flares (~50 s) can also be attributed to the free-fall time from the Alfven shell for a ~1e+13 G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.Comment: 20 pages, 18 figures, 3 tables, accepted for publication in the Astrophysical Journa

Molecular Serotype-Specific Identification of Non-Type B \u3cem\u3eHaemophilus influenzae\u3c/em\u3e by Loop-Mediated Isothermal Amplification

In children, the incidence of pneumococcal meningitis has decreased since the introduction of pneumococcal conjugate vaccine (PCV7 and PCV13). However, since the introduction of the vaccine, developed countries have seen the emergence of non-PCV13 serotypes. However, invasive pneumococcal disease (IPD) caused by PCV13-targeted serotypes still represents an important public health problem in resource-limited countries. To develop a rapid, simple, and cost-effective assay to detect serotypes of Streptococcus pneumoniae, we developed a novel loop-mediated isothermal amplification (LAMP) assay based on the sequences available for the 13 capsular types that are included in PCV13: 1, 3, 4, 5, 6 A, 6B, 7 F, 9 V, 14, 18 C, 19 A, 19 F, and 23 F. We evaluated test reactivity, specificity, sensitivity and performance, and compared the results between established LAMP and conventional PCR assays. To support its clinical use, the detection limits of the LAMP assay were evaluated using bacterial genomic DNA-spiked cerebrospinal fluid (CSF) and blood specimens. We confirmed the specificity of the LAMP assay using 41 serotypes of pneumococcal strains. The sensitivity of the LAMP assay was 10 to 100 copies per reaction, compared to 10 to 104 copies per reaction for PCR assays. The detection limits of the LAMP assay were comparable when using DNA-spiked CSF and blood specimens, as compared to using purified DNA as the template. In conclusion, a rapid and simple LAMP-based pneumococcal serotyping method has been developed. This is the first report of a LAMP method for a PCV13 serotype-specific identification assay, which could be a promising step to facilitate epidemiological studies of pneumococcal serotyping

WDR55 Is a Nucleolar Modulator of Ribosomal RNA Synthesis, Cell Cycle Progression, and Teleost Organ Development

The thymus is a vertebrate-specific organ where T lymphocytes are generated. Genetic programs that lead to thymus development are incompletely understood. We previously screened ethylnitrosourea-induced medaka mutants for recessive defects in thymus development. Here we report that one of those mutants is caused by a missense mutation in a gene encoding the previously uncharacterized protein WDR55 carrying the tryptophan-aspartate-repeat motif. We find that WDR55 is a novel nucleolar protein involved in the production of ribosomal RNA (rRNA). Defects in WDR55 cause aberrant accumulation of rRNA intermediates and cell cycle arrest. A mutation in WDR55 in zebrafish also leads to analogous defects in thymus development, whereas WDR55-null mice are lethal before implantation. These results indicate that WDR55 is a nuclear modulator of rRNA synthesis, cell cycle progression, and embryonic organogenesis including teleost thymus development