1,013 research outputs found
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
Structure-Guided Recombination Creates an Artificial Family of Cytochromes P450
Creating artificial protein families affords new opportunities to explore the determinants of structure and biological function free from many of the constraints of natural selection. We have created an artificial family comprising ~3,000 P450 heme proteins that correctly fold and incorporate a heme cofactor by recombining three cytochromes P450 at seven crossover locations chosen to minimize structural disruption. Members of this protein family differ from any known sequence at an average of 72 and by as many as 109 amino acids. Most (>73%) of the properly folded chimeric P450 heme proteins are catalytically active peroxygenases; some are more thermostable than the parent proteins. A multiple sequence alignment of 955 chimeras, including both folded and not, is a valuable resource for sequence-structure-function studies. Logistic regression analysis of the multiple sequence alignment identifies key structural contributions to cytochrome P450 heme incorporation and peroxygenase activity and suggests possible structural differences between parents CYP102A1 and CYP102A2
Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays
A galactic supernova remnant (SNR) Vela Jr. (RX J0852.04622, G266.61.2)
shows sharp filamentary structure on the north-western edge of the remnant in
the hard X-ray band. The filaments are so smooth and located on the most outer
side of the remnant. We measured the averaged scale width of the filaments
( and ) with excellent spatial resolution of {\it Chandra}, which are
in the order of the size of the point spread function of {\it Chandra} on the
upstream side and 49.5 (36.0--88.8) arcsec on the downstream side,
respectively. The spectra of the filaments are very hard and have no line-like
structure, and were well reproduced with an absorbed power-law model with
2.67 (2.55--2.77), or a {\tt SRCUT} model with = 4.3
(3.4--5.3) Hz under the assumption of . These results
imply that the hard X-rays are synchrotron radiation emitted by accelerated
electrons, as mentioned previously. Using a correlation between a function
and the SNR age, we estimated the
distance and the age of Vela Jr.: the estimated distance and age are 0.33
(0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are
consistent with previous reports, implying that --age relation may be
a useful tool to estimate the distance and the age of synchrotron X-ray
emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres
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
Discovery of Strong Radiative Recombination Continua from The Supernova Remnant IC 443 with Suzaku
We present the Suzaku spectroscopic study of the Galactic middle-aged
supernova remnant (SNR) IC 443. The X-ray spectrum in the 1.75-6.0 keV band is
described by an optically-thin thermal plasma with the electron temperature of
0.6 keV and several additional Lyman lines. We robustly detect, for the first
time, strong radiative recombination continua (RRC) of H-like Si and S around
at 2.7 and 3.5 keV. The ionization temperatures of Si and S determined from the
intensity ratios of the RRC to He-like K-alpha line are 1.0 keV and 1.2 keV,
respectively. We thus find firm evidence for an extremely-overionized
(recombining) plasma. As the origin of the overionization, a thermal conduction
scenario argued in previous work is not favored in our new results. We propose
that the highly-ionized gas were made at the initial phase of the SNR evolution
in dense regions around a massive progenitor, and the low electron temperature
is due to a rapid cooling by an adiabatic expansion.Comment: 5 pages, 5 figures, accepted by ApJ Lette
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