226 research outputs found
VETA-I x ray test analysis
This interim report presents some definitive results from our analysis of the VETA-I x-ray testing data. It also provides a description of the hardware and software used in the conduct of the VETA-I x-ray test program performed at the MSFC x-ray Calibration Facility (XRCF). These test results also serve to supply data and information to include in the TRW final report required by DPD 692, DR XC04. To provide an authoritative compendium of results, we have taken nine papers as published in the SPIE Symposium, 'Grazing Incidence X-ray/EUV Optics for Astronomy and Projection Lithography' and have reproduced them as the content of this report
VETA-1 x ray detection system
The alignment and X-ray imaging performance of the Advanced X-ray Astrophysics Facility (AXAF) Verification Engineering Test Article-I (VETA-I) was measured by the VETA-I X-Ray Detection System (VXDS). The VXDS was based on the X-ray detection system utilized in the AXAF Technology Mirror Assembly (TMA) program, upgraded to meet the more stringent requirements of the VETA-I test program. The VXDS includes two types of X-ray detectors: (1) a High Resolution Imager (HRI) which provides X-ray imaging capabilities, and (2) sealed and flow proportional counters which, in conjunction with apertures of various types and precision translation stages, provide the most accurate measurement of VETA-I performance. Herein we give an overview of the VXDS hardware including X-ray detectors, translation stages, apertures, proportional counters and flow counter gas supply system and associated electronics. We also describe the installation of the VXDS into the Marshall Space Flight Center (MSFC) X-Ray Calibration Facility (XRCF). We discuss in detail the design and performance of those elements of the VXDS which have not been discussed elsewhere; translation systems, flow counter gas supply system, apertures and thermal monitoring system
Sphinx measurements of the 2009 solar minimum x-ray emission
The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured
soft X-ray emission in the 1-15 keV energy range during the deep solar minimum
of 2009 with a sensitivity much greater than GOES. Several intervals are
identified when the X-ray flux was exceptionally low, and the flux and solar
X-ray luminosity are estimated. Spectral fits to the emission at these times
give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3
and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode
X-ray Telescope, we deduce that most of the emission is from general coronal
structures rather than confined features like bright points. For one of 27
intervals of exceptionally low activity identified in the SphinX data, the
Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT
(0.1-2.4 keV) was less than most nearby K and M dwarfs.Comment: Astrophysical Journal, in press. 14 pp, 3 figure
X-raying hot plasma in solar active regions with the SphinX spectrometer
The detection of very hot plasma in the quiescent corona is important for
diagnosing heating mechanisms. The presence and the amount of such hot plasma
is currently debated. The SphinX instrument on-board CORONAS-PHOTON mission is
sensitive to X-ray emission well above 1 keV and provides the opportunity to
detect the hot plasma component. We analyzed the X-ray spectra of the solar
corona collected by the SphinX spectrometer in May 2009 (when two active
regions were present). We modelled the spectrum extracted from the whole Sun
over a time window of 17 days in the 1.34-7 keV energy band by adopting the
latest release of the APED database. The SphinX broadband spectrum cannot be
modelled by a single isothermal component of optically thin plasma and two
components are necessary. In particular, the high statistics and the accurate
calibration of the spectrometer allowed us to detect a very hot component at ~7
million K with an emission measure of ~2.7 x 10^44 cm^-3. The X-ray emission
from the hot plasma dominates the solar X-ray spectrum above 4 keV. We checked
that this hot component is invariably present both at high and low emission
regimes, i.e. even excluding resolvable microflares. We also present and
discuss a possible non-thermal origin (compatible with a weak contribution from
thick-target bremsstrahlung) for this hard emission component. Our results
support the nanoflare scenario and might confirm that a minor flaring activity
is ever-present in the quiescent corona, as also inferred for the coronae of
other stars.Comment: 6 pages, 5 figures. Accepted for publication in A&
Similarity solutions for unsteady shear-stress-driven flow of Newtonian and power-law fluids : slender rivulets and dry patches
Unsteady flow of a thin film of a Newtonian fluid or a non-Newtonian power-law fluid with power-law index N driven by a constant shear stress applied at the free surface, on a plane inclined at an angle α to the horizontal, is considered. Unsteady similarity solutions representing flow of slender rivulets and flow around slender dry patches are obtained. Specifically, solutions are obtained for converging sessile rivulets (0 < α < π/2) and converging dry patches in a pendent film (π/2 < α < π), as well as for diverging pendent rivulets and diverging dry patches in a sessile film. These solutions predict that at any time t, the rivulet and dry patch widen or narrow according to |x|3/2, and the film thickens or thins according to |x|, where x denotes distance down the plane, and that at any station x, the rivulet and dry patch widen or narrow like |t|−1, and the film thickens or thins like |t|−1, independent of N
High-resolution x-ray telescopes
High-energy astrophysics is a relatively young scientific field, made
possible by space-borne telescopes. During the half-century history of x-ray
astronomy, the sensitivity of focusing x-ray telescopes-through finer angular
resolution and increased effective area-has improved by a factor of a 100
million. This technological advance has enabled numerous exciting discoveries
and increasingly detailed study of the high-energy universe-including accreting
(stellar-mass and super-massive) black holes, accreting and isolated neutron
stars, pulsar-wind nebulae, shocked plasma in supernova remnants, and hot
thermal plasma in clusters of galaxies. As the largest structures in the
universe, galaxy clusters constitute a unique laboratory for measuring the
gravitational effects of dark matter and of dark energy. Here, we review the
history of high-resolution x-ray telescopes and highlight some of the
scientific results enabled by these telescopes. Next, we describe the planned
next-generation x-ray-astronomy facility-the International X-ray Observatory
(IXO). We conclude with an overview of a concept for the next next-generation
facility-Generation X. The scientific objectives of such a mission will require
very large areas (about 10000 m2) of highly-nested lightweight
grazing-incidence mirrors with exceptional (about 0.1-arcsecond) angular
resolution. Achieving this angular resolution with lightweight mirrors will
likely require on-orbit adjustment of alignment and figure.Comment: 19 pages, 11 figures, SPIE Conference 7803 "Adaptive X-ray Optics",
part of SPIE Optics+Photonics 2010, San Diego CA, 2010 August 2-
Active X-ray Optics for Generation-X, the Next High Resolution X-ray Observatory
X-rays provide one of the few bands through which we can study the epoch of
reionization, when the first galaxies, black holes and stars were born. To
reach the sensitivity required to image these first discrete objects in the
universe needs a major advance in X-ray optics. Generation-X (Gen-X) is
currently the only X-ray astronomy mission concept that addresses this goal.
Gen-X aims to improve substantially on the Chandra angular resolution and to do
so with substantially larger effective area. These two goals can only be met if
a mirror technology can be developed that yields high angular resolution at
much lower mass/unit area than the Chandra optics, matching that of
Constellation-X (Con-X). We describe an approach to this goal based on active
X-ray optics that correct the mid-frequency departures from an ideal Wolter
optic on-orbit. We concentrate on the problems of sensing figure errors,
calculating the corrections required, and applying those corrections. The time
needed to make this in-flight calibration is reasonable. A laboratory version
of these optics has already been developed by others and is successfully
operating at synchrotron light sources. With only a moderate investment in
these optics the goals of Gen-X resolution can be realized.Comment: Enhanced version of SPIE presentation. 11 pages, 5 figure
Wildfires lead to decreased carbon and increased nitrogen concentrations in upland arctic streams
The Central Siberian Plateau is undergoing rapid climate change that has resulted in increased frequency of forest fires and subsequent alteration of watershed carbon and nutrient dynamics. Across a watershed chronosequence (3 to \u3e100 years since wildfire) we quantified the effects of fire on quantity and composition of dissolved organic matter (DOM), stream water nutrient concentrations, as well as in-stream nutrient uptake. Wildfires increased concentrations of nitrate for a decade, while decreasing concentrations of dissolved organic carbon and nitrogen (DOC and DON) and aliphatic DOM contribution for five decades. These post-wildfire changes in stream DOM result in lower uptake efficiency of in-stream nitrate in recently burned watersheds. Nitrate uptake (as uptake velocity) is strongly dependent on DOM composition (e.g. polyphenolics), ambient dissolved inorganic nitrogen (DIN), and DOC to DIN ratios. Our observations and experiments suggest that a decade-long pulse of inorganic nitrogen and a reduction of DOC export occur following wildfires in streams draining the Central Siberian Plateau. Increased fire frequency in the region is thus likely to both decrease DOM and increase nitrate delivery to the main stem Yenisei River, and ultimately the Arctic Ocean, in the coming decades
- …