405 research outputs found
Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board th e XMM/NEWTON satellite
We have used a mesh experiment in order to measure the sub-pixel structure of
the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40
m-square pixels which have an open electrode structure in order to improve
the detection efficiency for low-energy X-rays. We obtained restored pixel
images for various X-ray event grades (e.g. split-pixel events, single pixel
events, etc.) at various X-ray energies.
We confirmed that the open electrode structure results in a distorted
horizontal pixel boundary. The open electrode region generates both single
pixel events and vertically split events, but no horizontally split events.
Because the single pixel events usually show the best energy resolution, we
discuss a method of increasing the fraction of single pixel events from the
open electrode region. Furthermore, we have directly measured the thickness of
the electrodes and dead-layers by comparing spectra from the open electrode
region with those from the other regions: electrodes, electrode finger and
channel stop. We can say that EPIC MOS CCDs are more radiation hard than
front-illumination chips of ACIS on-board Chandra X-ray Observatory because of
their extra absorption thickness above the charge transfer channel. We
calcurated the mean pixel response and found that our estimation has a good
agreement with that of the ground calibration of EPIC MOS CCD.Comment: 20pages including 2 tables, 10 figures,Accepted for publication in :
Nuclear Instruments and Methods in Physics Research
Subpixel Spatial Resolution of the X-Ray Charge-Coupled Device Based on the Charge Cloud Shape
When an X-ray photon lands into a pixel (event pixel), the primary charge is
mainly collected into the event pixel. If the X-ray landing position is
sufficiently close to the pixel boundary, the primary charge spills over to the
adjacent pixel forming split events. We can easily understand that there are
three parameters coupled together; the X-ray landing position inside the pixel,
the X-ray event pattern and the primary charge cloud shape. We can determine
any one of them from the other two parameters. Since we know the charge cloud
shape using the multi-pitch mesh experiment, we can calculate the X-ray landing
position with subpixel resolution using the event pattern. We applied our
method to Ti-K X-rays for the charge-coupled device with m square
pixel. Once the primary charge splits into the adjacent pixel, we can determine
the X-ray landing position with subpixel resolution. Using three- or four-pixel
split events, we can determine the X-ray landing position with an accuracy of
less than m. For a two-pixel split event, we obtained a similar position
accuracy in the split direction with no improvement in the direction
perpendicular to it. We will discuss the type of CCD which can achieve the
subpixel resolution for the entire area of the CCD.Comment: 16pages, 5 figures. To appear in Jpn. J. Appl. Phys. March, 200
Spectroscopic Study of the Vela-Shrapnel
Several shrapnels have been detected in the vicinity of Vela SNR by the ROSAT
all-sky survey. We present here the spectral properties of shrapnel `A'
observed with the ASCA satellite. A prominent Si-K emission line with
relatively weak emission lines from other elements have been detected,
revealing that the relative abundance of Si is a few ten-times higher than
those of other elements. Combining with the ROSAT PSPC results, we obtained the
electron temperature, , to be keV. The total mass
of shrapnel `A' is estimated to be . If it is an ejecta of a
supernova explosion, the interstellar matter (ISM) would be swept up in the
leading edge while the ejecta material would be peeled off in the trailing
edge, which should be confirmed by future observations.Comment: 19pages, 5 figures, 1 table; Accepted for Publications of the
Astronomical Society of Japa
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
The Slow X-Ray Expansion of the Northwestern Rim of the Supernova Remnant RX J0852.0-4622
The detection of radioactive decay line of 44Ti provides a unique evidence
that the gamma-ray source is a young (< 1,000 yr) supernova remnant because of
its short lifetime of about 90 yr. Only two Galactic remnants, Cassiopeia A and
RX J0852.0-4622, are hitherto reported to be the 44Ti line emitter, although
the detection from the latter has been debated. Here we report on an expansion
measurement of the northwestern rim of RX J0852.0-4622 obtained with X-ray
observations separated by 6.5 yr. The expansion rate is derived to be
0.023+/-0.006% that is about five times lower than those of young historical
remnants. Such a slow expansion suggests that RX J0852.0-4622 is not a young
remnant as has been expected. We estimate the age of 1,700-4,300 yr of this
remnant depending on its evolutionary stage. Assuming a high shock speed of
about 3000 km/sec, which is suggested by the detection of non-thermal X-ray
radiation, the distance of about 750 pc to this remnant is also derived.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical
Journal Letter
First Detection of Ar-K Line Emission from the Cygnus Loop
We observed the Cygnus Loop with XMM-Newton (9 pointings) and Suzaku (32
pointings) between 2002 and 2008. The total effective exposure time is 670.2
ks. By using all of the available data, we intended to improve a
signal-to-noise ratio of the spectrum. Accordingly, the accumulated spectra
obtained by the XIS and the EPIC show some line features around 3 keV that are
attributed to the S He and Ar He lines, respectively. Since the
Cygnus Loop is an evolved (10,000 yr) supernova remnant whose temperature
is relatively low (1 keV) compared with other young remnants, its spectrum
is generally faint above 3.0 keV, no emission lines, such as the Ar-K line have
ever been detected. The detection of the Ar-K line is the first time and we
found that its abundance is significantly higher than that of the solar value;
9.0 and 8.4 (in units of solar), estimated from
the XIS and the EPIC spectra, respectively. We conclude that the Ar-K line
originated from the ejecta of the Cygnus Loop. Follow-up X-ray observations to
tightly constrain the abundances of Ar-rich ejecta will be useful to accurately
estimate the progenitor's mass.Comment: 12 pages, 9 figures, accepted for publication in PAS
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