113 research outputs found
X-ray tracing using Geant4
We describe an extension to the Geant4 software package that allows it to be
used as a general purpose X-ray tracing package. We demonstrate its use by
building a model of the X-ray optics of the XMM-Newton, calculating its
effective area, and comparing the results with the published calibration
curves.Comment: 9 pages, 5 figures, accepted for publication by NIMA, DOI know
Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes
Grazing incidence mirrors for X-ray astronomy are usually designed in the
parabola-hyperbola (Wolter I) configuration. This design allows for optimal
images on-axis, which however degrade rapidly with the off-axis angle. Mirror
surfaces described by polynomia (with terms higher than order two), have been
put forward to improve the performances over the field of view. Here we present
a refined procedure aimed at optimizing wide-field grazing incidence telescopes
for X-ray astronomy. We improve the angular resolution over existing
(wide-field) designs by ~ 20%. We further consider the corrections for the
different plate scale and focal plane curvature of the mirror shells, which
sharpen by another ~ 20% the image quality. This results in a factor of ~ 2
reduction in the observing time needed to achieve the same sensitivity over
existing wide-field designs and of ~ 5 over Wolter I telescopes. We demonstrate
that such wide-field X-ray telescopes are highly advantageous for deep surveys
of the X-ray sky.Comment: 8 pages 4 figures. Accepted for publication on A&A (macro included
Image analysis of the AXAF VETA-I x ray mirror
Initial core scan data of the VETA-I x-ray mirror proved disappointing, showing considerable unpredicted image structure and poor measured FWHM. 2-D core scans were performed, providing important insight into the nature of the distortion. Image deconvolutions using a ray traced model PSF was performed successfully to reinforce our conclusion regarding the origin of the astigmatism. A mechanical correction was made to the optical structure, and the mirror was tested successfully (FWHM 0.22 arcsec) as a result
Research study on stellar X-ray imaging experiment, volume 2
A review of the scientific objectives of an integrated X-ray orbiting telescope facility is presented. A set of observations to be conducted to achieve the objectives of the research are described. The techniques and equipment used in the experiment are defined. The configuration of the facility and the specifications of the test equipment are included
Chandra Temperature Maps for Galaxy Clusters with Radio Halos
We analyze Chandra temperature maps for a sample of clusters with high
quality radio halo data, to study the origin of the radio halos. The sample
includes A520, A665, A754, A773, A1914, A2163, A2218, A2319, and 1E0657-56. We
present new temperature maps for all but two of them (A520 and A754). All these
clusters exhibit distorted X-ray morphology and strong gas temperature
variations indicating ongoing mergers. Some clusters, e.g., A520, A665,
1E0657-56, exhibit the previously reported spatial correlation between the
radio halo brightness and the hot gas regions. However, it is not a general
feature. While most mergers are too messy to allow us to disentangle the
projection effects, we find clear counterexamples (e.g., A754 and A773) where
the hottest gas regions do not exhibit radio emission at the present
sensitivity level. This cannot be explained by projection effects, and
therefore argues against merger shocks -- at least those relatively weak ones
responsible for the observed temperature structure in most clusters -- as the
main mechanism for the halo generation. This leaves merger-generated turbulence
as a more likely mechanism. The two clusters with the clearest radio brightness
- temperature correlation, A520 and 1E0657-56, are both mergers in which a
small dense subcluster has just passed through the main cluster, very likely
generating turbulence in its wake. The maximum radio brightness and the hot gas
are both seen in these wake regions. On the other hand, the halos in 1E0657-56
and A665 (both high-velocity mergers) extend into the shock regions in front of
the subclusters, where no strong turbulence is expected. Thus, in high-velocity
(M=2-3) mergers, both shock and turbulence acceleration mechanisms may be
significant.Comment: 17 pages, 9 color figures, uses emulateapj. Version with better
resolution figures at http://hea-www.harvard.edu/~maxim/papers/rhalos_tmaps/
. ApJ in pres
The x ray reflectivity of the AXAF VETA-I optics
The x-ray reflectivity of the VETA-I optic, the outermost shell of the AXAF x-ray telescope, with a bare Zerodur surface, is measured and compared with theoretical predictions. Measurements made at energies of 0.28, 0.9, 1.5, 2.1, and 2.3 keV are compared with predictions based on ray trace calculations. The data were obtained at the x-ray calibrations facility at Marshall Space Flight Center with an electron impact x-ray source located 528 m from the grazing incidence mirror. The source used photoelectric absorption filters to eliminate bremsstrahlung continuum. The mirror has a diameter of 1.2 m and a focal length of 10 m. The incident and reflected x-ray flux are detected using two proportional counters, one located in the incident beam of x-rays at the entrance aperture of the VETA-I, and the other in the focal plane behind an aperture of variable size. Results on the variation of the reflectivity with energy as well as the absolute value of the reflectivity are presented. We also present a synchrotron reflectivity measurement with high energy resolution over the range 0.26 to 1.8 keV on a flat Zerodur sample, done at NSLS. We present evidence for contamination of the flat by a thin layer of carbon on the surface, and the possibility of alteration of the surface composition of the VETA-I mirror perhaps by the polishing technique. The overall agreement between the measured and calculated effective area of VETA-I is between 2.6 percent and 10 percent, depending on which model for the surface composition is adopted. Measurements at individual energies deviate from the best-fitting calculation to 0.3 to 0.8 percent, averaging 0.6 percent at energies below the high energy cutoff of the mirror reflectivity, and are as high as 20.7 percent at the cutoff. We also discuss the approach to the final preflight calibration of the full AXAF flight mirror
Evolution of the cluster X-ray scaling relations since z>0.4
We derive correlations between X-ray temperature, luminosity, and gas mass
for a sample of 22 distant, z>0.4, galaxy clusters observed with Chandra. We
detect evolution in all three correlations between z>0.4 and the present epoch.
In particular, in the Omega=0.3, Lambda=0.7 cosmology, the luminosity
corresponding to a fixed temperature scales approximately as (1+z)**(1.5+-0.3);
the gas mass for a fixed luminosity scales as (1+z)**(-1.8+-0.4); and the gas
mass for a fixed temperature scales as (1+z)**(-0.5+-0.4) (all uncertainties
are 90% confidence). We briefly discuss the implication of these results for
cluster evolution models.Comment: submitted to ApJ Letter
Advanced X-ray Astrophysics Facility (AXAF): An overview
The Advanced X-ray Astrophysics Facility (AXAF) is the x-ray component of NASA's Great Observatories. To be launched in late 1998, AXAF will provide unprecedented capabilities for high-resolution imaging, spectrometric imaging, and high-resolution disperse spectroscopy, over the x-ray band from about 0.1 keV to 10 keV. With these capabilities, AXAF observations will address many of the outstanding questions in astronomy, astrophysics, and cosmology
Configuring a Graphical User Interface for Managing Local HYSPLIT Model Runs Through AWIPS
Responding to incidents involving the release of harmful airborne pollutants is a continual challenge for Weather Forecast Offices in the National Weather Service. When such incidents occur, current protocol recommends forecaster-initiated requests of NOAA's Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model output through the National Centers of Environmental Prediction to obtain critical dispersion guidance. Individual requests are submitted manually through a secured web site, with desired multiple requests submitted in sequence, for the purpose of obtaining useful trajectory and concentration forecasts associated with the significant release of harmful chemical gases, radiation, wildfire smoke, etc., into local the atmosphere. To help manage the local HYSPLIT for both routine and emergency use, a graphical user interface was designed for operational efficiency. The interface allows forecasters to quickly determine the current HYSPLIT configuration for the list of predefined sites (e.g., fixed sites and floating sites), and to make any necessary adjustments to key parameters such as Input Model. Number of Forecast Hours, etc. When using the interface, forecasters will obtain desired output more confidently and without the danger of corrupting essential configuration files
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