6,300 research outputs found
The Plasma Structure of the Cygnus Loop from the Northeastern Rim to the Southwestern Rim
The Cygnus Loop was observed from the northeast to the southwest with
XMM-Newton. We divided the observed region into two parts, the north path and
the south path, and studied the X-ray spectra along two paths. The spectra can
be well fitted either by a one-component non-equilibrium ionization (NEI) model
or by a two-component NEI model. The rim regions can be well fitted by a
one-component model with relatively low \kTe whose metal abundances are
sub-solar (0.1--0.2). The major part of the paths requires a two-component
model. Due to projection effects, we concluded that the low kTe (about 0.2 keV)
component surrounds the high kTe (about 0.6 keV) component, with the latter
having relatively high metal abundances (about 5 times solar). Since the Cygnus
Loop is thought to originate in a cavity explosion, the low-kTe component
originates from the cavity wall while the high-kTe component originates from
the ejecta. The flux of the cavity wall component shows a large variation along
our path. We found it to be very thin in the south-west region, suggesting a
blowout along our line of sight. The metal distribution inside the ejecta shows
non-uniformity, depending on the element. O, Ne and Mg are relatively more
abundant in the outer region while Si, S and Fe are concentrated in the inner
region, with all metals showing strong asymmetry. This observational evidence
implies an asymmetric explosion of the progenitor star. The abundance of the
ejecta also indicates the progenitor star to be about 15 M_sun.Comment: 24 pages, 9 figures, Astrophysical Journal in pres
On the Nature of AX J2049.6+2939 and AX J2050.0+2914
AX J2049.6+2939 is a compact X-ray source in the vicinity of the southern
blow-up region of the Cygnus Loop supernova remnant (Miyata et al. 1998a). This
source was the brightest X-ray source inside the
Cygnus Loop observed during the ASCA survey project. The X-ray spectrum was
well fitted by a power-law function with a photon index of . Short-term timing analysis was performed and no coherent pulsation
was found. Follow-up observations with ASCA have revealed a large variation in
X-ray intensity by a factor of 50, whereas the spectral shape did not
change within the statistical uncertainties. In the second ASCA observation, we
found another X-ray source, AX J2050.0+2941, at the north east of AX
J2049.6+2939. During the three ASCA observations, the X-ray intensity of AX
J2050.0+2941 varied by a factor of 4. No coherent pulsations could be
found for AX J2050.0+2941.
We have performed optical photometric and spectroscopic observations in the
vicinity of AX J2049.6+2939 at the Kitt Peak National Observatory
(KPNO). As a result, all objects brighter than -band magnitude of 22 in
the error box can be identified with normal stars. Combined with the
X-ray results and the fact that there are no radio counterparts, AX
J2049.6+2939 is not likely to be either an ordinary rotation-powered pulsar
or an AGN. The nature of AX J2049.6+2939 is still unclear and further
observations over a wide energy band are strongly required.
As to AX J2050.0+2941, the long-term X-ray variability and the radio
counterpart suggests that it is an AGN.Comment: 23 pages, 4 figures, Accepted for publication by Astrophysical
Journa
Turbulent boundary layer around a group of obstacles in the direction of flow
Results of an investigation of a boundary layer in a turbulent flow on the surface of a wall having a group of obstacles on the path of flow are presented with regard to the mean velocity field, velocity distribution of the two dimensional flow, wall surface shear stresses and Reynolds stresses measured in a downstream cross section where an interference of boundary layers takes place in a flow around adjacent obstacles arranged on the path of flow
Discovery of the compact X-ray source inside the Cygnus Loop
We detected an X-ray compact source inside the Cygnus Loop during the
observation project of the whole Cygnus Loop with the ASCA GIS. The source
intensity is 0.11 c s for GIS and 0.15 c s for SIS, which is the
strongest in the ASCA band. The X-ray spectra are well fitted by a power law
spectrum of a photon index of \error{-2.1}{0.1} with neutral H column of
(\error{3.1}{0.6}). Taking into account the
interstellar absorption feature, this source is X-ray bright mainly above 1 keV
suggesting either an AGN or a rotating neutron star. So far, we did not detect
intensity variation nor coherent pulsation mainly due to the limited
observation time. There are several optical bright stellar objects within the
error region of the X-ray image. We carried out the optical spectroscopy for
the brightest source (V=+12.6) and found it to be a G star. The follow up deep
observation both in optical and in X-ray wavelengths are strongly required.Comment: Accepted for Publications of the Astronomical Society of Japan 17
pages, 3 figur
Ionization States and Plasma Structures of Mixed-morphology SNRs Observed with ASCA
We present the results of a systematic study using ASCA of the ionization
state for six ``mixed-morphology'' supernova emnants (MMSNRs): IC 443, W49B,
W28, W44, 3C391, and Kes 27. MMSNRs show centrally filled thermal X-ray
emission, which contrasts to shell-like radio morphology, a set of
haracteristics at odds with the standard model of SNR evolution (e.g., the
Sedov model). We have therefore studied the evolution of the MMSNRs from the
ionization conditions inferred from the X-ray spectra, independent of X-ray
morphology. We find highly ionized plasmas approaching ionization equilibrium
in all the mmsnrs. The degree of ionization is systematically higher than the
plasma usually seen in shell-like SNRs. Radial temperature gradients are also
observed in five remnants, with cooler plasma toward the limb. In IC 443 and
W49B, we find a plasma structure consistent with shell-like SNRs, suggesting
that at least some MMSNRs have experienced similar evolution to shell-like
SNRs. In addition to the results above, we have discovered an ``overionized''
ionization state in W49B, in addition to that previously found in IC 443.
Thermal conduction can cause the hot interior plasma to become overionized by
reducing the temperature and density gradients, leading to an interior density
increase and temperature decrease. Therefore, we suggest that the
``center-filled'' X-ray morphology develops as the result of thermal
conduction, and should arise in all SNRs. This is consistent with the results
that MMSNRs are near collisional ionization equilibrium since the conduction
timescale is roughly similar to the ionization timescale. Hence, we conclude
that MMSNRs are those that have evolved over yr. We call this phase
as the ``conduction phase.''Comment: 34 pages, 20 figures, 9 tables, accepted for publication in The
Astrophysical Journa
Kiso observations for 20 GRBs in HETE-2 era
We have established a GRB follow-up observation system at Kiso observatory
(Japan) in 2001. Since the east Asian area had been blank for the GRB follow-up
observational network, this observational system is very important in studying
the temporal and spectral evolution of early afterglows. Using this system, we
have performed quick observations for optical afterglows from early phase based
on HETE-2 and INTEGRAL alerts. Thanks to the quick follow-up observation
system, we have been able to use the Kiso observatory in 20 events, and conduct
their follow-up observations in optical and near infrared wavelengths.Comment: 5 pages, 4 figure. Accepted for publication into "il nuovo cimento".
Proceeding of the 4th Rome GRB conference, eds. L. Piro, L. Amati, S. Covino,
B. Gendr
Physical Relation of Source I to IRc2 in the Orion KL Region
We present mid-infrared narrow-band images of the Orion BN/KL region, and
N-band low-resolution spectra of IRc2 and the nearby radio source "I." The
distributions of the silicate absorption strength and the color temperature
have been revealed with a sub-arcsecond resolution. The detailed structure of
the 7.8 micron/12.4 micron color temperature distribution was resolved in the
vicinity of IRc2. A mid-infrared counterpart to source I has been detected as a
large color temperature peak. The color temperature distribution shows an
increasing gradient from IRc2 toward source I, and no dominant temperature peak
is seen at IRc2. The spectral energy distribution of IRc2 could be fitted by a
two-temperature component model, and the "warmer component" of the infrared
emission from IRc2 could be reproduced by scattering of radiation from source
I. IRc2 itself is not self-luminous, but is illuminated and heated by an
embedded luminous young stellar object located at source I.Comment: 20 pages, 11 figures. Minor corrections had been done in the ver.2.
Accepted for publication in PAS
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