224 research outputs found
光導波機能を有する相分離シンチレータ材料の開発と高分解能X線イメージングへの応用に関する研究
要約のみTohoku University吉川彰課
The ASCA Medium Sensitivity Survey (the GIS Catalog Project): Source Counts and Evidence for Emerging Population of Hard Sources
We present first results from the ASCA Medium Sensitivity Survey (AMSS; or
the GIS catalog project). From the serendipitous fields amounting to 106
degE-2, we determined the Log N - Log S relations in the 0.7-7 keV and 2-10 keV
bands with the best statistical accuracy obtained so far, over the flux range
from 1 x 10E-11 to 5 x 10E-14 and 7 x 10E-14 erg sE-1 cmE-2, respectively. When
the sources detected in the 0.7-7 keV band are divided into two subsamples with
higher and lower spectral hardness, the former exhibits a significantly steeper
slope than the latter at fluxes below ~10E-12 erg sE-1 cmE-2 (0.7-7 keV). The
average spectrum of sources becomes continuously harder toward fainter fluxes,
from a photon index of 2.1 in the 0.7-10 keV range at the flux of ~10E-11 to
1.6 at ~10E-13 erg sE-1 cmE-2 (0.7-7 keV). This is consistent with the
comparison of source counts between the 2-10 keV and the 0.7-2 keV band, and
solves the puzzle of their discrepancy reported previously. Our results
demonstrate rapid emergence of hard X-ray sources with a decreasing flux from
\~10E-12 to ~10E-13 erg sE-1 cmE-2 (2-10 keV).Comment: 10 pages, 3 figures (including 2 color figures). Accepted for
publication in ApJ
The hardest X-ray source in the ASCA Large Sky Survey: Discovery of a new type 2 Seyfert
We present results of ASCA deep exposure observations of the hardest X-ray
source discovered in the ASCA Large Sky Survey (LSS) project, designated as AX
J131501+3141. We extract its accurate X-ray spectrum, taking account of the
contamination from a nearby soft source (AX J131502+3142), separated only by
1'. AX J131501+3141 exhibits a large absorption of NH = (6 +4 -2)x 10^22 H/cm^2
with a photon index \Gamma = 1.5 +0.7 -0.6. The 2--10 keV flux was about 5 x
10^-13 erg/s/cm^2 and was time variable by a factor of 30% in 0.5 year. From
the highly absorbed X-ray spectrum and the time variability, as well as the
results of the optical follow-up observations (Akiyama et al. 1998,
astro-ph/9801173), we conclude that AX J131501+3141 is a type 2 Seyfert galaxy.
Discovery of such a low flux and highly absorbed X-ray source could have a
significant impact on the origin of the cosmic X-ray background.Comment: 16 pages, 6 figures, requires AAS Latex macro v4.0, to appear in The
Astrophysical Journal, text and figures also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/sakano/work/paper/index-e.htm
Erratum: ASCA Observations of the Absorption-Line Features from the Super-Luminal Jet Source GRS 1915+105
We have discovered errors in the calculation of some of the Einstein
coefficients in Table 5 and some plots in Figure 3. Due to the errors, the
square-root section of the curves of growth of Fe xxvi Ka and Kb, and Ni xxviii
Ka in Figure 3 were a few times underestimated. We correct Table 5 and re-plot
Figure 3 together with the unaffected curves. The program to calculate the
corrected curves of growth is available at
http://www.hp.phys.titech.ac.jp/kotani/cog/index.htmlComment: Erratum with 1 table and 1 figure submitted to ApJ. Original paper
include
An Open-labeled, Multicenter Phase II Study of Tamibarotene in Patients with Steroid-refractory Chronic Graft-versus-Host Disease
Chronic graft-versus-host disease (GVHD) is a major cause of late death and morbidity following allogeneic hematopoietic cell transplantation (HSCT). Retinoic acid (tamibarotene) exerts multiple effects on cell differentiation and is clinically used for the treatment of acute promyelocytic leukemia. Tamibarotene down-regulates both Th1 and Th17 differentiation in donor T cells after allogeneic HSCT, resulting in attenuation of experimental chronic GVHD. Based on preclinical data, we have launched a phase II study of tamibarotene in patients with steroid-refractory chronic GVHD. This study will clarify whether tamibarotene can exert beneficial effects in patients with steroid-refractory chronic GVHD
HER2 G776S mutation promotes oncogenic potential in colorectal cancer cells when accompanied by loss of APC function
Clinical cancer genome sequencing detects oncogenic variants that are potential targets for cancer treatment, but it also detects variants of unknown significance. These variants may interact with each other to influence tumor pathophysiology, however, such interactions have not been fully elucidated. Additionally, the effect of target therapy for those variants also unclarified. In this study, we investigated the biological functions of a HER2 mutation (G776S mutation) of unknown pathological significance, which was detected together with APC mutation by cancer genome sequencing of samples from a colorectal cancer (CRC) patient. Transfection of the HER2 G776S mutation alone slightly increased the kinase activity and phosphorylation of HER2 protein, but did not activate HER2 downstream signaling or alter the cell phenotype. On the other hand, the HER2 G776S mutation was shown to have strong oncogenic potential when loss of APC function was accompanied. We revealed that loss of APC function increased Wnt pathway activity but also increased RAS-GTP, which increased ERK phosphorylation triggered by HER2 G776S transfection. In addition, afatinib, a pan-HER tyrosine kinase inhibitor, suppressed tumor growth in xenografts derived from HER2 G776S-transfected CRC cells. These findings suggest that this HER2 mutation in CRC may be a potential therapeutic target
Optical Identification of the ASCA Lynx Deep Survey: An Association of QSOs and a Supercluster at z=1.3?
Results of optical identification of the ASCA Lynx deep survey are presented.
Six X-ray sources are detected in the 2-7 keV band using the SIS in a 20'x20'
field of view with fluxes larger than ~4x10^{-14} erg s-1 cm-2 in the band.
Follow-up optical spectroscopic observations were made, and five out of six
sources are identified with AGNs/QSOs at redshifts of 0.5-1.3. We also identify
two more additional X-ray sources detected in a soft X-ray band with AGNs/QSOs.
It is found that three QSOs identified are located at z~1.3. Two rich clusters
and several groups of galaxies are also placed at the same redshift in the
surveyed field, and projected separations between the QSOs and the clusters are
3-8 Mpc at the redshift.Comment: 15 pages with 3 figures. Accepted to Ap
Log N - Log S Relations and Spectral Properties of Sources from the ASCA Large Sky Survey --- their Implications for the Origin of the Cosmic X-ray Background (CXB)
We carried out the first wide-area unbiased survey with the ASCA satellite in
the 0.7-10 keV band around a north Galactic-pole region covering a continuous
area of 7 square degrees (Large Sky Survey; LSS). To make the best use of ASCA
capability, we developed a new source-detection method where the complicated
detector responses are fully taken into account. Applying this method to the
entire LSS data independently in the total (0.7-7 keV), hard (2-10 keV), and
soft (0.7-2 keV) band, we detected 107 sources altogether with sensitivity
limits of 6 x 10E-14 (0.7-7 keV), 1 x 10E-13 (2-10 keV), and 2 x 10E-14 erg
sE-1 cmE-2 (0.7-2 keV), respectively. A complete list of the detected sources
is presented. Based on detailed studies by Monte Carlo simulations, we
evaluated effects of the source confusion and accurately derived Log N - Log S
relation in each survey band. The Log N - Log S relation in the hard band is
located on the extrapolation from the GINGA and HEAO1 results with the
Euclidean slope of -3/2, while that in the soft band is consistent with the
results by ROSAT. At these flux limits, 30 (+/- 3) percent of the CXB in the
0.7-7 keV band and 23 (+/- 3) percent in the 2-10 keV band have been resolved
into discrete sources. The average spectrum of faint sources detected in the
total band shows a photon index of 1.63 +/- 0.07 in the 0.7-10 keV range,
consistent with the comparison of source counts between the hard and the soft
energy band. Those detected in the hard band show a photon index of 1.49 +/-
0.10 in the 2-10 keV range. These spectral properties suggest that contribution
of sources with hard energy spectra become significant at a flux of 10E-13 erg
sE-1 cmE-2 (2-10 keV). The most plausible candidates are type-II AGNs, as
indicated by on-going optical identifications.Comment: 28 pages, 11 figures, to appear in ApJ 518, 1999; figure 1 replaced,
minor errors in text correcte
The Nature of Ultra-Luminous Compact X-Ray Sources in Nearby Spiral Galaxies
Studies were made of ASCA spectra of seven ultra-luminous compact X-ray
sources (ULXs) in nearby spiral galaxies; M33 X-8 (Takano et al. 1994), M81 X-6
(Fabbiano 1988b; Kohmura et al. 1994; Uno 1997), IC 342 Source 1 (Okada et al.
1998), Dwingeloo 1 X-1 (Reynolds et al. 1997), NGC 1313 Source B (Fabbiano &
Trinchieri 1987; Petre et al. 1994), and two sources in NGC 4565 (Mizuno et al.
1999). With the 0.5--10 keV luminosities in the range 10^{39-40} ergs/s, 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 these seven sources have been described successfully
with so called multi-color disk blackbody (MCD) emission arising from
optically-thick standard accretion disks around black holes. Except 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 solar masses. 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.Comment: submitted to ApJ, December 199
- …