397 research outputs found
Metal Rich Plasma at the Center Portion of the Cygnus Loop
We observed the center portion of the Cygnus Loop supernova remnant with the
ASCA observatory. The X-ray spectrum of the center portion was significantly
different from that obtained at the North-East (NE) limb. The emission lines
from Si and S were quite strong while those of O and the continuum emission
were similar to those obtained at the NE limb. Based on the spectral analysis,
Si and S emission lines originated from a high-kTe and low ionization plasma
whereas O and most of the continuum emission arose from a low-kTe and high
ionization plasma. We suppose that Si and S emitting gas are present at the
interior of the Loop while O lines and continuum emission mainly arise from the
shell region. Therefore, we subtracted the spectrum of the NE limb from that of
the center. Obtained abundances of Si, S, and Fe were 4 1, 6 2, and
times higher than those of the cosmic abundances,
respectively, and are 40 times richer than those obtained at the NE limb.
These facts strongly support that some of the crude ejecta must be left at the
center portion of the Cygnus Loop. The low abundance of Fe relative to Si and S
suggests a type II SN with a massive progenitor star as the origin of the
Cygnus Loop.Comment: Accepted for Publications of the Astronomical Society of Japan, 40
pages, 12 Postscript figures, uses PASJ95.sty, PASJadd.sty, and psbox.st
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
Reflection Shocked Gas in the Cygnus Loop Supernova Remnant
We performed spectroscopic X-ray observations of the eastern and northern
regions of the Cygnus Loop with the ASCA observatory. The
X-ray surface brightness of these regions shows a complex structure in the
ROSAT all-sky survey image. We carried out a spatially-resolved analysis for
both regions and found that did not increase toward the center
region, but showed inhomogeneous structures. Such variation cannot be explained
by a blast wave model propagating into a homogeneous interstellar medium. We
thus investigated the interaction between a blast wave and an interstellar
cloud. Two major emission mechanisms are plausible: a cloud evaporation model
and a reflection shock model. In both regions, only a reflection shock model
qualitatively explains our results. Our results suggest the existence of a
large-scale interstellar cloud. We suppose that such a large-scale structure
would be produced by a precursor.Comment: 27 pages, 15 figures. Accepted for publication of ApJ. High
resolution and color figures are available at
http://wwwxray.ess.sci.osaka-u.ac.jp/~miyata/paper/cygloop_reflection.pd
Spatially Resolved X-ray Spectroscopy of Vela Shrapnel A
We present the detailed X-ray spectroscopy of Vela shrapnel A with the
XMM-Newton satellite. Vela shrapnel A is one of several protrusions identified
as bullets from Vela supernova explosion. The XMM-Newton image shows that
shrapnel A consists of a bright knot and a faint trailing wake. We extracted
spectra from various regions, finding a prominent Si Ly emission line
in all the spectra. All the spectra are well represented by the non-equilibrium
ionization (NEI) model. The abundances are estimated to be O0.3,
Ne0.9, Mg0.8, Si3, Fe0.8 times their solar values. The
non-solar abundance ratio between O and Si indicates that shrapnel A originates
from a deep layer of a progenitor star. We found that the relative abundances
between heavy elements are almost uniform in shrapnel A, which suggests that
the ejecta from supernova explosion are well mixed with swept-up interstellar
medium.Comment: 11 pages, 10 figures, ApJ 10 May 2006, v642 2 issu
Scattering and Iron Fluorescence Revealed During Absorption Dips in Circinus X-1
We show that dramatic spectral evolution associated with dips occurring near
phase zero in RXTE observations of Cir X-1 is well-fit by variable and at times
heavy absorption (N_H > 10^24 cm^-2) of a bright component, plus an underlying
faint component which is not attenuated by the variable column and whose flux
is ~10% of that of the unabsorbed bright component. A prominent Fe emission
line at ~6.5 keV is evident during the dips. The absolute line flux outside the
dips is similar to that during the dips, indicating that the line is associated
with the faint component. These results are consistent with a model in which
the bright component is radiation received directly from a compact source while
the faint component may be attributed to scattered radiation. Our results are
also generally consistent with those of Brandt et al., who found that a
partial- covering model could explain ASCA spectra of a low-to-high transition
in Cir X-1. The relative brightness of the two components in our model requires
a column density of ~2*10^23 cm^-2 if the faint component is due to Thomson
scattering in material that mostly surrounds the source. We find that
illumination of such a scattering cloud by the observed direct component would
produce an Fe K-alpha fluorescence flux that is in rough agreement with the
flux of the observed emission line. We also conclude that if the scattering
medium is not highly ionized, our line of sight to the compact source does not
pass through it. Finally, we discuss simple pictures of the absorbers
responsible for the dips themselves.Comment: Accepted for publication in The Astrophysical Journal (23 pages,
including 11 figures
Wide band X-ray Imager (WXI) and Soft Gamma-ray Detector (SGD) for the NeXT Mission
The NeXT mission has been proposed to study high-energy non-thermal phenomena
in the universe. The high-energy response of the super mirror will enable us to
perform the first sensitive imaging observations up to 80 keV. The focal plane
detector, which combines a fully depleted X-ray CCD and a pixellated CdTe
detector, will provide spectra and images in the wide energy range from 0.5 keV
to 80 keV. In the soft gamma-ray band up to ~1 MeV, a narrow field-of-view
Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe
detector will provide precise spectra with much higher sensitivity than present
instruments. The continuum sensitivity will reach several times 10^(-8)
photons/s/keV/cm^(2) in the hard X-ray region and a few times10^(-7)
photons/s/keV/cm^(2) in the soft gamma-ray region.Comment: 12 pages, 13 figures, to be published in the SPIE proceedings 5488,
typo corrected in sec.
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
Performance of the Charge Injection Capability of Suzaku XIS
A charge injection technique is applied to the X-ray CCD camera, XIS (X-ray
Imaging Spectrometer) onboard Suzaku. The charge transfer inefficiency (CTI) in
each CCD column (vertical transfer channel) is measured by the injection of
charge packets into a transfer channel and subsequent readout. This paper
reports the performances of the charge injection capability based on the ground
experiments using a radiation damaged device, and in-orbit measurements of the
XIS. The ground experiments show that charges are stably injected with the
dispersion of 91eV in FWHM in a specific column for the charges equivalent to
the X-ray energy of 5.1keV. This dispersion width is significantly smaller than
that of the X-ray events of 113eV (FWHM) at approximately the same energy. The
amount of charge loss during transfer in a specific column, which is measured
with the charge injection capability, is consistent with that measured with the
calibration source. These results indicate that the charge injection technique
can accurately measure column-dependent charge losses rather than the
calibration sources. The column-to-column CTI correction to the calibration
source spectra significantly reduces the line widths compared to those with a
column-averaged CTI correction (from 193eV to 173eV in FWHM on an average at
the time of one year after the launch). In addition, this method significantly
reduces the low energy tail in the line profile of the calibration source
spectrum.Comment: Paper contains 18 figures and 15 tables. Accepted for publication in
PAS
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