134 research outputs found
Refining Chandra/ACIS Subpixel Event Repositioning Using a Backside Illuminated CCD Model
Subpixel event repositioning (SER) techniques have been demonstrated to
significantly improve the already unprecedented spatial resolution of Chandra
X-ray imaging with the Advanced CCD Imaging Spectrometer (ACIS). Chandra CCD
SER techniques are based on the premise that the impact position of events can
be refined, based on the distribution of charge among affected CCD pixels. ACIS
SER models proposed thus far are restricted to corner split (3- and 4-pixel)
events, and assume that such events take place at the split pixel corners. To
improve the event counting statistics, we modified the ACIS SER algorithms to
include 2-pixel split events and single pixel events, using refined estimates
for photon impact locations. Furthermore, simulations that make use of a
high-fidelity backside illuminated (BI) CCD model demonstrate that mean photon
impact positions for split events are energy dependent leading to further
modification of subpixel event locations according to event type and energy,
for BI ACIS devices. Testing on Chandra CCD X-ray observations of the Orion
Nebula Cluster indicates that these modified SER algorithms further improve the
spatial resolution of Chandra/ACIS, to the extent that the spreading in the
spatial distribution of photons is dominated by the High Resolution Mirror
Assembly, rather than by ACIS pixelization.Comment: 23 pages, 8 figures, 2nd version, submitted to Ap
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Application of Design of Experiments (DOE) on the Processing of Rapid Prototyped Samples
The purpose of this experiment was to improve the Fused Deposition Modeling Process by
examining the tensile strength of samples fabricated in a Stratasys FDM 1650 Machine utilizing
the methods of Design of Experiments. A two-level, four-factor, full factorial experiment was
conducted. The selected factors were temperature, air gap, slice thickness, and raster orientation.
A regression equation determined the level each factor should be set in order to optimize the
FDM machine settings. It was found that single factors - small air gap, small layer thickness
and low raster orientation, as well as the interaction between high temperature and small layer
thickness yielded the greatest effect the response.Mechanical Engineerin
Stationary quasivariational inequalities with gradient constraint and nonhomogeneous boundary conditions
Publicado em "From particle systems to partial differential equations. Part 2. (Springer proceedings in mathematics & statistics, vol. 75). ISBN 978-3-642-54270-1We study existence of solution of stationary uasivariational inequalities with gradient constraint and nonhomogeneous boundary condition of Neumann or Dirichlet type.
Through two different approaches, one making use of a fixed point theorem and the other using a process of regularization and penalization, we obtain different sufficient conditions for the existence of solution.(undefined
A Persistent Disk Wind in GRS 1915+105 with NICER
The bright, erratic black hole X-ray binary GRS 1915+105 has long been a
target for studies of disk instabilities, radio/infrared jets, and accretion
disk winds, with implications that often apply to sources that do not exhibit
its exotic X-ray variability. With the launch of NICER, we have a new
opportunity to study the disk wind in GRS 1915+105 and its variability on short
and long timescales. Here we present our analysis of 39 NICER observations of
GRS 1915+105 collected during five months of the mission data validation and
verification phase, focusing on Fe XXV and Fe XXVI absorption. We report the
detection of strong Fe XXVI in 32 (>80%) of these observations, with another
four marginal detections; Fe XXV is less common, but both likely arise in the
well-known disk wind. We explore how the properties of this wind depends on
broad characteristics of the X-ray lightcurve: mean count rate, hardness ratio,
and fractional RMS variability. The trends with count rate and RMS are
consistent with an average wind column density that is fairly steady between
observations but varies rapidly with the source on timescales of seconds. The
line dependence on spectral hardness echoes known behavior of disk winds in
outbursts of Galactic black holes; these results clearly indicate that NICER is
a powerful tool for studying black hole winds.Comment: Accepted for publication in ApJL. Comments welcom
Chandra/ACIS Subpixel Event Repositioning. II. Further Refinements and Comparison between Backside and Front-side Illuminated X-ray CCDs
We further investigate subpixel event repositioning (SER) algorithms in
application to Chandra X-ray Observatory (CXO) CCD imaging. SER algorithms have
been applied to backside illuminated (BI) Advanced CCD Imaging Spectrometer
(ACIS) devices, and demonstrate spatial resolution improvements in Chandra/ACIS
observations. Here a new SER algorithm that is charge split dependent is added
to the SER family. We describe the application of SER algorithms to frontside
illuminated (FI) ACIS devices. The results of SER for FI CCDs are compared with
those obtained from SER techniques applied to BI CCD event data. Both simulated
data and Chandra/ACIS observations of the Orion Nebular Cluster were used to
test and evaluate the achievement of the various SER techniques.Comment: 30 pages, 9 figures, submitted to Ap
Scientific, Back-Illuminated CCD Development for the Transiting Exoplanet Survey Satellite
We describe the development of the fully depleted, back illuminated charge coupled devices for the Transiting Exoplanet Survey Satellite, which includes a set of four wide angle telescopes, each having a 2x2 array of CCDs. The devices are fabricated on the newly upgraded 200-mm wafer line at Lincoln Laboratory. We discuss methods used to produce the devices and present early performance results from the 100- micron thick, 15x15-microns, 2k x 4k pixel frame transfer CCDs
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
HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component
An exceptionally intense gamma-ray burst, GRB030329, was detected and
localized by the instruments on board the High Energy Transient Explorer
satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two
\~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The
energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making
GRB030329 one of the brightest GRBs ever detected. Communication of a 2 arcmin
error box 73 minutes after the burst allowed the rapid detection of a
counterpart in the optical, X-ray, radio and the ensuing discovery of a
supernova with most unusual characteristics. Analyses of the burst lightcurves
reveal the presence of a distinct, bright, soft X-ray component underlying the
main GRB: the 2-10 keV fluence of this component is ~7e-6 erg/cm2. The main
pulses of GRB030329 were preceded by two soft, faint, non-thermal bumps. We
present details of the HETE observations of GRB030329.Comment: 22 pages, 5 figures, to be published in ApJ 617, no. 2 (10 December
2004). Referee comments have been incorporated; results of improved spectral
analysis are include
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