596 research outputs found
High Angular Resolution, Sensitive CS J=2-1 and J=3-2 Imaging of the Protostar L1551 NE: Evidence for Outflow-Triggered Star Formation ?
High angular resolution and sensitive aperture synthesis observations of CS
() and CS () emissions toward L1551 NE, the second brightest
protostar in the Taurus Molecular Cloud, made with the Nobeyama Millimeter
Array are presented. L1551 NE is categorized as a class 0 object deeply
embedded in the red-shifted outflow lobe of L1551 IRS 5. Previous studies of
the L1551 NE region in CS emission revealed the presence of shell-like
components open toward L1551 IRS 5, which seem to trace low-velocity shocks in
the swept-up shell driven by the outflow from L1551 IRS 5. In this study,
significant CS emission around L1551 NE was detected at the eastern tip of the
swept-up shell from = 5.3 km s to 10.1 km s, and
the total mass of the dense gas is estimated to be 0.18 0.02 .
Additionally, the following new structures were successfully revealed: a
compact disklike component with a size of 1000 AU just at L1551 NE,
an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of
AU, i.e., a bow shock, and a distinct velocity gradient of the
dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. These
features suggest that the CS emission traces the post-shocked region where the
dense gas associated with L1551 NE and the swept-up shell of the outflow from
L1551 IRS 5 interact. Since the age of L1551 NE is comparable to the timescale
of the interaction, it is plausible that the formation of L1551 NE was induced
by the outflow impact. The compact structure of L1551 NE with a tiny envelope
was also revealed, suggesting that the outer envelope of L1551 NE has been
blown off by the outflow from L1551 IRS 5.Comment: 29 pages, 12 figures, Accepted for Publication in the Astrophysical
Journa
XMM-Newton observation of the persistent Be/NS X-ray binary pulsar RX J1037.5-5647 in a low luminosity state
The spectra of several X-ray binary pulsars display a clear soft excess,
which in most cases can be described with a blackbody model, above the main
power-law component. While in the high-luminosity sources it is usually
characterized by low temperature (kT
100 km), in the two persistent and low-luminosity pulsars 4U 0352+309 and RX
J0146.9+6121 this component has a high temperature (kT > 1 keV) and a smaller
radius (R < 0.5 km), consistent with the estimated size of the neutron-star
polar cap. Here we report on the timing and spectral analysis of RX
J1037.5-5647, another low-luminosity persistent Be binary pulsar, based on the
first XMM-Newton observation of this source. We have found a best-fit period P
= 853.4(+/-0.2) s, that implies an average pulsar spin-up dP/dt ~ -2E-8 s/s in
the latest decade. The estimated source luminosity is Lx ~ 10^34 erg/s, a value
comparable to that of the other persistent Be binary pulsars and about one
order of magnitude lower than in most of the previous measurements. The source
spectrum can be described with a power law plus blackbody model, with kTbb =
1.26(+0.16/-0.09) keV and Rbb = 128(+13/-21) m, suggesting a polar-cap origin
of this component. These results strengthen the hypothesis that, in addition to
low luminosities and long periods, this class of sources is characterized also
by common spectral propertiesComment: 9 pages, 8 figures, 2 tables. Accepted for publication by Astronomy
and Astrophysic
Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX
We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line.Comment: 12 pages, 8 figures, Accepted for publication in Ap
Study of a Threshold Cherenkov Counter Based on Silica Aerogels with Low Refractive Indices
To identify and in the region of GeV/c, a
threshold Cherenkov counter equipped with silica aerogels has been
investigated. Silica aerogels with a low refractive index of 1.013 have been
successfully produced using a new technique. By making use of these aerogels as
radiators, we have constructed a Cherenkov counter and have checked its
properties in a test beam. The obtained results have demonstrated that our
aerogel was transparent enough to make up for loss of the Cherenkov photon
yield due to a low refractive index. Various configurations for the photon
collection system and some types of photomultipliers, such as the fine-mesh
type, for a read out were also tested. From these studies, our design of a
Cherenkov counter dedicated to separation up to a few GeV/c %in the
momentum range of GeV/c with an efficiency greater than \%
was considered.Comment: 21 pages, latex format (article), figures included, to be published
in Nucl. Instrm. Meth.
A Study of the Populations of X-ray Sources in the Small Magellanic Cloud with ASCA
The Advanced Satellite for Cosmology and Astrophysics (ASCA) has made
multiple observations of the Small Magellanic Cloud (SMC). X-ray mosaic images
in the soft (0.7--2.0 keV) and hard (2.0--7.0 keV) bands are separately
constructed, and the latter provides the first hard X-ray view of the SMC. We
extract 39 sources from the two-band images with a criterion of S/N>5, and
conduct timing and spectral analyses for all of these sources. Coherent
pulsations are detected from 12 X-ray sources; five of which are new
discoveries. Most of the 12 X-ray pulsars are found to exhibit long-term flux
variabilities, hence they are likely to be X-ray binary pulsars (XBPs). On the
other hand, we classify four supernova remnants (SNRs) as thermal SNRs, because
their spectra exhibit emission lines from highly ionized atoms. We find that
XBPs and thermal SNRs in the SMC can be clearly separated by their hardness
ratio (the ratio of the count rate between the hard and soft bands). Using this
empirical grouping, we find many XBP candidates in the SMC, although no
pulsations have yet been detected from these sources. Possible implications on
the star-formation history and evolution of the SMC are presented by a
comparison of the source populations in the SMC and our Galaxy.Comment: 11 pages, 39 Figures, to be published in ApJ Supplement. Tables (body
and figures also) are available at
http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job
Discovery of a new Transient X-ray Pulsar in the Small Magellanic Cloud
Rossi X-Ray Timing Explorer observations of the Small Magellanic Cloud have
revealed a previously unknown transient X-ray pulsar with a pulse period of
95s. Provisionally designated XTE SMC95, the pulsar was detected in three
Proportional Counter Array observations during an outburst spanning 4 weeks in
March/April 1999. The pulse profile is double peaked reaching a pulse fraction
\~0.8. The source is proposed as a Be/neutron star system on the basis of its
pulsations, transient nature and characteristically hard X-ray spectrum. The
2-10 keV X-ray luminosity implied by our observations is > 2x10^37 erg/s which
is consistent with that of normal outbursts seen in Galactic systems. This
discovery adds to the emerging picture of the SMC as containing an extremely
dense population of transient high mass X-ray binaries.Comment: Accepted by A&A. 7 pages, 6 figure
The binary period and outburst behaviour of the SMC X-ray binary pulsar system SXP504
A probable binary period has been detected in the optical counterpart to the
X-ray source CXOU J005455.6-724510 = RX J0054.9-7245 = AXJ0054.8-7244 = SXP504
in the Small Magellanic Cloud. This source was detected by Chandra on 04 Jul
2002 and subsequently observed by XMM-Newton on 18 Dec 2003. The source is
coincident with an Optical Gravitational Lensing (OGLE) object in the
lightcurves of which several optical outburst peaks are visible at ~ 268 day
intervals. Timing analysis shows a period of 268.6 +/- 0.1 days at > 99%
significance. Archival Rossi X-ray Timing Explorer (RXTE) data for the 504s
pulse-period has revealed detections which correspond closely with predicted or
actual peaks in the optical data. The relationship between this orbital period
and the pulse period of 504s is within the normal variance found in the Corbet
diagram.Comment: Accepted by MNRAS. 1 LATEX page. 4 figure
Serine tRNA complementary to the nonuniversal serine codon CUG in Candida cylindracea: evolutionary implications.
CS-Net: Channel and Spatial Attention Network for Curvilinear Structure Segmentation
The detection of curvilinear structures in medical images, e.g., blood vessels or nerve fibers, is important in aiding management of many diseases. In this work, we propose a general unifying curvilinear structure segmentation network that works on different medical imaging modalities: optical coherence tomography angiography (OCT-A), color fundus image, and corneal confocal microscopy (CCM). Instead of the U-Net based convolutional neural network, we propose a novel network (CS-Net) which includes a self-attention mechanism in the encoder and decoder. Two types of attention modules are utilized - spatial attention and channel attention, to further integrate local features with their global dependencies adaptively. The proposed network has been validated on five datasets: two color fundus datasets, two corneal nerve datasets and one OCT-A dataset. Experimental results show that our method outperforms state-of-the-art methods, for example, sensitivities of corneal nerve fiber segmentation were at least 2% higher than the competitors. As a complementary output, we made manual annotations of two corneal nerve datasets which have been released for public access
The Search for High-Mass X-ray Binaries in the Phoenix Dwarf Galaxy
We report on the first X-ray images of the Phoenix dwarf galaxy, taken with
\emph{XMM-Newton} in July 2009. This local group dwarf galaxy shares
similarities with the Small Magellanic Cloud (SMC) including a burst of star
formation 50 Myr ago. The SMC has an abundance of High Mass X-ray
Binaries (HMXBs) and so we have investigated the possibility of an HMXB
population in Phoenix with the intention of furthering the understanding of the
HMXB-star formation rate relation. The data from the combined European Photon
Imaging Cameras (EPIC) were used to distinguish between different source
classes (foreground stars, background galaxies, AGN and supernova remnants)
using EPIC hardness ratios and correlations with optical and radio catalogues.
Of the 81 X-ray sources in the field of view, six are foreground stars, four
are galaxies and one is an AGN. The remaining sources with optical counterparts
have log() consistent with AGN in the local universe.
Further investigation of five sources in the field of view suggests they are
all background AGN. Their position behind the gas cloud associated with Phoenix
makes them a possible tool for further probing the metallicity of this region.
We find no evidence for any HMXBs in Phoenix at this time. This rules out the
existence of the X-ray persistent supergiant X-ray binary systems. However the
transient nature of the Be/X-ray binaries means we cannot rule out a population
of these sources but can conclude that it is not extensive.Comment: 13 pages, 4 figures, 4 tables, Accepted for publication in MNRA
- …