289 research outputs found
Chandra Observations of a Non-Thermal Supernova Remnant Candidate AX J1843.8-0352 and its Surroundings
We present the Chandra results of AX J1843.8-0352, a supernova remnant (SNR)
recently identified with ASCA. Chandra spatially resolved two components from
this SNR: non-thermal and thermal ones. The morphology of the non-thermal
component is clumpy and elliptical, elongated from the north to the south with
a mean diameter of about 9 arcmin. The spectrum is fitted with a power-law
model of photon index 2.1 and the east rim is associated with the non-thermal
radio sources C and F (Helfand et al. 1989). Therefore the non-thermal
component is probably synchrotron X-rays by energetic electrons accelerated at
the shell of the SNR. The thermal component is the brightest clump located
within the non-thermal component and shows a spectrum of a thin plasma of about
0.7 keV temperature. Notable discovery is its peculiar morphology; a head of 50
arcsec x 30 arcsec size near the south-east rim of the SNR and a 30 arcsec-long
``jet'' pointing to the southwest. Although this emission is associated with
the west part of the radio source F, the absorption is twice larger than that
of the non-thermal X-rays, or the bulk of the SNR emission. Therefore, it is
unclear whether this peculiar plasma is a thermal component associated with AX
J1843.8-0352, a Galactic source located in the far side of our Galaxy, or an
extragalactic source.Comment: 19 pages, 5 figures; to appear in Ap
Discovery of the Slowest X-Ray Pulsar in the SMC, AX J0049.5-7323, with ASCA
The discovery of coherent pulsations with ASCA from an X-ray source, AX
J0049.5-7323, is reported. The barycentric period was determined to be 755.5
+/- 0.6 s, which is the longest among X-ray pulsators in the SMC. The X-ray
spectrum has been found to be unchanged through ASCA observations, with a
photon index of ~0.8 and a luminosity of ~5e35 erg s^-1 (0.7-10 keV). Archival
data of the Einstein and the ROSAT satellites indicate that the flux has been <
1e-12 erg s^-1 cm^-2 (< 5e35 erg s^-1) for over 20 years and exhibits a
variability with a factor of >10. We argue that AX J0049.5-7323 is an X-ray
pulsar with a Be star companion.Comment: 4 pages, 4 figures, to be published in PASJ. Also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job
Fish assemblages associated with three types of artificial reefs: density of assemblages and possible impacts on adjacent fish abundance
We evaluated the effectiveness of wooden artificial reefs (ARs) as fish habitat. Three types of ARs, made of cedar logs, broadleaf tree logs, and PVC pipes, respectively,
were deployed in triplicate at 8-m depth off Maizuru, Kyoto Prefecture, Sea of Japan, in May 2004. Fish assemblages associated with each of the nine ARs were observed by using
SCUBA twice a month for four years. Fish assemblages in the adjacent habitat were also monitored for two years before and four years after reef deployment. In the surveyed areas
(ca. 10 m2) associated with each of the cedar, broadleaf, and PVC ARs, the average number of fish species was 4.14, 3.49, and 3.00, and the average number of individuals was 40.7, 27.9, and 20.3, respectively. The estimated biomass was also more greater when associated with the cedar ARs than with other ARs. Visual censuses of the habitat adjacent to the ARs revealed that the number of fish species and the density of individuals were not affected by the deployment of the ARs. Our results support the superiority of cedar as an AR material and indicate that deployment of wooden ARs causes no reduction of fish abundance in adjacent natural reefs
Discovery of a Transient X-Ray Pulsar, AX J1841.0-0536, in the Scutum Arm Region with ASCA
We report on the discovery of a transient X-ray pulsar, AX J1841.0-0536,
serendipitously found in the Scutum arm region with the ASCA in two separate
observations. The X-ray flux is very faint at the beginning, but exhibits two
flares in the second observation. The flare flux increases by a factor 10
within only about 1 hr. Coherent pulsations with a period of 4.7394 plus/minus
0.0008 s were detected in the brightest flare phase. The X-ray spectra in the
quiescent and flare phases were fitted with an absorbed power-law model with a
photon index about 1 plus a narrow Gaussian line at the center energy of 6.4
keV. The interstellar column density of about 3E22 /cm2 may indicate that AX
J1841.0-0536 is located at a tangential point of the Scutum arm at about 10 kpc
distance. The coherent pulsations, large flux variability and the spectral
shape suggest that AX J1841.0-0536 is a Be/X-ray binary pulsar.Comment: 5 pages, 8 figures, uses pasj00.cls; accepted by Publication of the
Astronomical Society of Japa
Precocious activation of APC/C-Cdh1 at pre-anaphase causes genome instability
Faithful chromosome segregation and thereby accurate gene transmission are crucial for all organisms. Until proper attachment of the mitotic spindle to the kinetochore is established, the ubiquitin ligase (E3) Cdc20-activated APC/C (anaphase promoting complex/cyclosome) is repressed by the spindle assembly checkpoint (SAC) and sister chromatin cohesion is protected. Mutants defective in SAC fail to arrest at metaphase even in the presence of damaged microtubules. Interestingly, a similar phenomenon occurs in yeast cells defective in Bub2, a negative factor of the mitotic exit network (MEN), which is required for telophase onset, although its precise molecular mechanism is unknown. Here, we show that chromosome missegregation occurs frequently in bub2∆ cells in the presence of damaged microtubules. The loss of Bub2 caused precocious activation of APC/C-Cdh1/Hct1 at pre-anaphase, leading to securin degradation and then separase-mediated cohesin cleavage. Overexpression of CDH1 and CDC14, encoding Cdc14 phosphatase, at pre-anaphase similarly caused chromosome missegregation. Thus, sequential activation of APC/C-Cdc20 and then APC/C-Cdh1 is critical for precise chromosome segregation and precocious activation of APC/C-Cdh1 at pre-anaphase causes genomic instability. Since degradation of human securin is also mediated by APC/C-Cdc20 and APC/C-Cdh1, this study predicts that precocious activation APC/C-Cdh1 in human cells similarly causes genomic instability, and thereby cell death or tumorigenesis
X-Ray Emission from Supernova Remnants Observed in the ASCA Galactic Plane Survey
X-ray images and spectra of 5 cataloged supernova remnants (SNRs), G12.0-0.1,
G346.6-0.2, G348.5+0.1, G348.7+0.3, and G355.6-0.0, observed in the ASCA
galactic plane survey are presented. The sizes of X-ray emission from
G12.0-0.1, G348.5+0.1, G348.7+0.3, and G355.6-0.0 are comparable to their radio
structures, while that of G346.6-0.2 is smaller than the radio structure. The
X-ray spectra of all of the SNRs were heavily absorbed by interstellar matter
with N_H>10^{22} cm^{-2}. The spectrum of G355.6-0.0 exhibited emission lines,
indicating that the X-ray emission has a thin thermal plasma origin, and was
well represented by two-temperature thin thermal emission model. On the other
hand, no clear emission line features were found in the spectra of the others
and the spectra could be represented by either a thin thermal emission model or
a power-law model.Comment: Accepted for publication in PAS
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