250 research outputs found
Registration of the First Thermonuclear X-ray Burst from AX J1754.2-2754
During the analysis of the INTEGRAL observatory archival data we found a
powerful X-ray burst, registered by JEM-X and IBIS/ISGRI telescopes on April
16, 2005 from a weak and poorly known source AX J1754.2-2754. Analysis of the
burst profiles and spectrum shows, that it was a type I burst, which result
from thermonuclear explosion on the surface of nutron star. It means that we
can consider AX J1754.2-2754 as an X-ray burster. Certain features of burst
profile at its initial stage witness of a radiation presure driven strong
expansion and a corresponding cooling of the nutron star photosphere. Assuming,
that the luminosity of the source at this phase was close to the Eddington
limit, we estimated the distance to the burst source d=6.6+/-0.3 kpc (for
hidrogen atmosphere of the neutron star) and d=9.2+/-0.4 kpc (for helium
atmosphere).Comment: 12 pages, 6 figure
Kondo Effect in Multiple-Dot Systems
We study the Kondo effect in multiple-dot systems for which the inter- as
well as intra-dot Coulomb repulsions are strong, and the inter-dot tunneling is
small. The application of the Ward-Takahashi identity to the inter-dot
dynamical susceptibility enables us to analytically calculate the conductance
for a double-dot system by using the Bethe-ansatz exact solution of the SU(4)
impurity Anderson model. It is clarified how the inter-dot Kondo effect
enhances or suppresses the conductance under the control of the gate voltage
and the magnetic field. We then extend our analysis to multiple-dot systems
including more than two dots, and discuss their characteristic transport
properties by taking a triple-dot system as an example.Comment: 8 pages, 9 figure
AX J1749.1-2733 and AX J1749.2-2725 - the close pair of X-ray pulsars behind the Galactic Center: an optical identification
Two faint X-ray pulsars, AX J1749.2-2725 and AX J1749.1-2733, located in the
direction to the Galactic Center, were studied in detail using data of
INTEGRAL, XMM-Newton and Chandra observatories in X-rays, the SOFI/NTT
instrument in infrared and the RTT150 telescope in optics. X-ray positions of
both sources were determined with the uncertainty better than ~1 arcsec, that
allowed us to identify their infrared counterparts. From the subsequent
analysis of infrared and optical data we conclude that counterparts of both
pulsars are likely massive stars of B0-B3 classes located behind the Galactic
Center at distances of 12-20 kpc, depending on the type, probably in further
parts of galactic spiral arms. In addition, we investigated the extinction law
towards the galactic bulge and found that it is significantly different from
standard one.Comment: 6 pages, 7 figures, will be published in MNRA
Hard X-ray Bursts Recorded by the IBIS Telescope of the INTEGRAL Observatory in 2003-2009
To find X-ray bursts from sources within the field of view of the
IBIS/INTEGRAL telescope, we have analysed all the archival data of the
telescope available at the time of writing the paper (the observations from
January 2003 to April 2009). We have detected 834 hard (15-25 keV) X-ray
bursts, 239 of which were simultaneously recorded by the JEM-X/INTEGRAL
telescope in the standard X-ray energy range. More than 70% of all bursts (587
events) have been recorded from the well-known X-ray burster GX 354-0. We have
found upper limits on the distances to their sources by assuming that the
Eddington luminosity limit was reached at the brightness maximum of the
brightest bursts.Comment: 18 pages, 2 figures, 2 table
ASCA X-ray source catalogue in the Galactic Center region
The ASCA satellite made 107 pointing observations on a 5 x 5 deg^2 region
around the center of our Milky Way Galaxy (the Galactic Center) from 1993 to
1999. In the X-ray images of the 0.7--3 keV or 3--10 keV bands, we found 52
point sources and a dozen diffuse sources. All the point sources are uniformly
fitted with an absorbed power-law model. For selected bright sources, Sgr A*,
AX J1745.6-2901, A 1742-294, SLX 1744-300, GRO J1744-28, SLX 1737-282, GRS
1734-292, AX J1749.2-2725, KS 1741-293, GRS 1741.9-2853, and an unusual flare
source XTE J1739-302, we present further detailed spectral and timing analyses,
and discuss their nature.
The dozen extended X-ray sources comprise radio supernova remnants, giant
molecular clouds, and some new discoveries. Most show emission lines from
either highly ionized atoms or low-ionized irons.
The X-ray spectra were fitted with either a thin thermal or power-law model.
This paper summarizes the results and provides the ASCA X-ray source catalogue
in the Galactic Center region.Comment: 33 pages, 8 figures, Accepted for publication in ApJS, also found in
http://www.star.le.ac.uk/~mas/research/paper/#Sakano2001apj
Raman and Infrared-Active Phonons in Hexagonal HoMnO Single Crystals: Magnetic Ordering Effects
Polarized Raman scattering and infrared reflection spectra of hexagonal
HoMnO single crystals in the temperature range 10-300 K are reported.
Group-theoretical analysis is performed and scattering selection rules for the
second order scattering processes are presented. Based on the results of
lattice dynamics calculations, performed within the shell model, the observed
lines in the spectra are assigned to definite lattice vibrations. The magnetic
ordering of Mn ions, which occurs below T=76 K, is shown to effect both
Raman- and infrared-active phonons, which modulate Mn-O-Mn bonds and,
consequently, Mn exchange interaction.Comment: 8 pages, 6 figure
OH (1720 MHz) Masers and Mixed-Morphology Supernova Remnants
Radio surveys of supernova remnants (SNRs) in the Galaxy have uncovered 19
SNRs accompanied by OH maser emission at 1720 MHz. This unusual class of maser
sources is suggested to be produced behind a shock front from the expansion of
a supernova remnant running into a molecular cloud. An important ingredient of
this model is that X-ray emission from the remnant enhances the production of
OH molecule. The role of X-ray emission from maser emitting (ME) SNRs is
investigated by comparing the X-ray induced ionization rate with theory. One
aspect of this model is verified: there is a strong association between maser
emitting and mixed-morphology (MM) or thermal composite SNRs --center-filled
thermal X-ray emission surrounded by shell-like radio morphology. We also
present ROSAT and ASCA observations of two maser emitting SNRs: G21.8--0.6 (Kes
69) and G357.7--0.1 (Tornado).Comment: 13 pages, 2 tables, 1 figure, ApJ (in press
Further studies of 1E 1740.7-2942 with ASCA
We report the ASCA results of the Great Annihilator 1E 1740.7-2942 obtained
with five pointing observations in a time span of 3.5 years. The X-ray spectrum
for each period is well fitted with a single power-law absorbed by a high
column of gas. The X-ray flux changes by a factor of 2 from period to period,
but the other spectral parameters show no significant change. The photon index
is flat with \Gamma = 0.9--1.3. The column densities of hydrogen N_H is
1.0 x 10^{23} H cm^{-2} and that of iron N_{Fe} is 10^{19} Fe cm^{-2}.
These large column densities indicate that 1E 1740.7-2942 is near at the
Galactic Center. The column density ratio leads the iron abundance to be 2
times larger than the other elements in a unit of the solar ratio. The
equivalent width of the K\alpha-line from a neutral iron is less than 15 eV in
90% confidence. This indicates that the iron column density within several
parsecs from 1E 1740.7-2942 is less than 5 x 10^{17} Fe cm^{-2}. In addition,
the derived hydrogen column density is about 1/6 of that of giant molecular
clouds in the line of sight. All these facts support that 1E 1740.7-2942 is not
in a molecular cloud, but possibly in front of it; the X-rays are not powered
by accretion from a molecular cloud, but from a companion star like ordinary
X-ray binaries.Comment: To appear in ApJ July 20, 1999 issue, Vol. 520 #1, 23 pages LaTeX
files, uses aasms4.sty and psfig.sty, also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/sakano/work/paper/index-e.htm
Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe
We investigate the surface electronic structures of polar 1T'-MoTe2, the Weyl
semimetal candidate realized through the nonpolar-polar structural phase
transition, by utilizing the laser angle-resolved photoemission spectroscopy
(ARPES) combined with first-principles calculations. Two kinds of domains with
different surface band dispersions are observed from a single-crystalline
sample. The spin-resolved measurements further reveal that the spin
polarizations of the surface and the bulk-derived states show the different
domain-dependences, indicating the opposite bulk polarity. For both domains,
some segment-like band features resembling the Fermi arcs are clearly observed.
The patterns of the arcs present the marked contrast between the two domains,
respectively agreeing well with the slab calculation of (0 0 1) and (0 0 -1)
surfaces. The present result strongly suggests that the Fermi arc connects the
identical pair of Weyl nodes on one side of the polar crystal surface, whereas
it connects between the different pairs of Weyl nodes on the other side.Comment: 13 pages, 4 figure
Optical Identification of the ASCA Large Sky Survey
We present results of optical identification of the X-ray sources detected in
the ASCA Large Sky Survey. Optical spectroscopic observations were done for 34
X-ray sources which were detected with the SIS in the 2-7 keV band above 3.5
sigma. The sources are identified with 30 AGNs, 2 clusters of galaxies, and 1
galactic star. Only 1 source is still unidentified. The flux limit of the
sample corresponds to 1 x 10^{-13} erg s^{-1} cm^{-2} in the 2-10 keV band.
Based on the sample, the paper discusses optical and X-ray spectral
properties of the AGNs, contribution of the sources to the Cosmic X-ray
Background, and redshift and luminosity distributions of the AGNs. An
interesting result is that the redshift distribution of the AGNs suggests a
deficiency of high-redshift (0.5 10^{44}
erg s^{-1}) absorbed narrow-line AGNs (so called type 2 QSOs).Comment: Accepted for publication in ApJ. 57 pages with 13 figures, 9 JPG
plates, 5 additional PS tables. Original EPS plates (gzipped format
~1Mbyte/plate) and TeX tables are available from
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/akiyama/0001289
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