87 research outputs found
Recommended from our members
The impact of low energy proton damage on the operational characteristics of EPIC-MOS CCDs
The University of Tübingen 3.5 MeV Van de Graaf accelerator facility was used to investigate the effect of low energy protons on the performance of the European Photon Imaging Camera (EPIC), metal–oxide semiconductor (MOS), charge coupled devices (CCDs). Two CCDs were irradiated in different parts of their detecting areas using different proton spectra and dose rates. Iron-55 was the calibration source in all cases and was used to measure any increases in charge transfer inefficiency (CTI) and spectral resolution of the CCDs. Additional changes in the CCD bright pixel table and changes in the low X-ray energy response of the device were examined.
The Monte Carlo code Stopping Range of Ions in Matter (SRIM) was used to model the effect of a 10 MeV equivalent fluence of protons interacting with the CCD. Since the non-ionising energy loss (NIEL) function could not be applied effectively at such low proton energies. From the 10 MeV values, the expected CTI degradation could be calculated and then compared to the measured CTI changes
An XMM-Newton observation of the extreme Narrow Line Seyfert 1 Galaxy, Mrk 359
We present XMM-Newton observations of Mrk 359, the first Narrow Line Seyfert
1 galaxy discovered. Even among NLS1s, Mrk 359 is an extreme case with
extraordinarily narrow optical emission lines. The XMM-Newton data show that
Mrk 359 has a significant soft X-ray excess which displays only weak absorption
and emission features. The (2-10) keV continuum, including reflection, is
flatter than the typical NLS1, with Gamma approximately 1.84. A strong emission
line of equivalent width approximately 200 eV is also observed, centred near
6.4 keV. We fit this emission with two line components of approximately equal
strength: a broad iron-line from an accretion disc and a narrow, unresolved
core. The unresolved line core has an equivalent width of approximately 120 eV
and is consistent with fluorescence from neutral iron in distant reprocessing
gas, possibly in the form of a `molecular torus'. Comparison of the narrow-line
strengths in Mrk 359 and other low-moderate luminosity Seyfert 1 galaxies with
those in QSOs suggests that the solid angle subtended by the distant
reprocessing gas decreases with increasing AGN luminosity.Comment: Accepted for publication in MNRA
An X-ray polarimeter for hard X-ray optics
Development of multi-layer optics makes feasible the use of X-ray telescope
at energy up to 60-80 keV: in this paper we discuss the extension of
photoelectric polarimeter based on Micro Pattern Gas Chamber to high energy
X-rays. We calculated the sensitivity with Neon and Argon based mixtures at
high pressure with thick absorption gap: placing the MPGC at focus of a next
generation multi-layer optics, galatic and extragalactic X-ray polarimetry can
be done up till 30 keV.Comment: 12 pages, 7 figure
X-ray polarimetry on-board HXMT
The development of micropixel gas detectors, capable to image tracks produced
in a gas by photoelectrons, makes possible to perform polarimetry of X-ray
celestial sources in the focus of grazing incidence X-ray telescopes. HXMT is a
mission by the Chinese Space Agency aimed to survey the Hard X-ray Sky with
Phoswich detectors, by exploitation of the direct demodulation technique. Since
a fraction of the HXMT time will be spent on dedicated pointing of particular
sources, it could host, with moderate additional resources a pair of X-ray
telescopes, each with a photoelectric X-ray polarimeter (EXP2, Efficient X-ray
Photoelectric Polarimeter) in the focal plane. We present the design of the
telescopes and the focal plane instrumentation and discuss the performance of
this instrument to detect the degree and angle of linear polarization of some
representative sources. Notwithstanding the limited resources, the proposed
instrument can represent a breakthrough in X-ray Polarimetry.Comment: 10 pages, 7 figure
Early anthropogenic transformation of the Danube-Black Sea system
© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 2 (2012): 582, doi:10.1038/srep00582.Over the last century humans have altered the export of fluvial materials leading to significant changes in morphology, chemistry, and biology of the coastal ocean. Here we present sedimentary, paleoenvironmental and paleogenetic evidence to show that the Black Sea, a nearly enclosed marine basin, was affected by land use long before the changes of the Industrial Era. Although watershed hydroclimate was spatially and temporally variable over the last ~3000 years, surface salinity dropped systematically in the Black Sea. Sediment loads delivered by Danube River, the main tributary of the Black Sea, significantly increased as land use intensified in the last two millennia, which led to a rapid expansion of its delta. Lastly, proliferation of diatoms and dinoflagellates over the last five to six centuries, when intensive deforestation occurred in Eastern Europe, points to an anthropogenic pulse of river-borne nutrients that radically transformed the food web structure in the Black Sea.This study was supported by grants OISE 0637108, EAR
0952146, OCE 0602423 and OCE 0825020 from the National Science Foundation and
grants from the Woods Hole Oceanographic Institution
A photoelectric polarimeter for XEUS: a new window in x-ray sky
XEUS is a large area telescope aiming to rise X-ray Astronomy to the level of
Optical Astronomy in terms of collecting areas. It will be based on two
satellites, locked on a formation flight, one with the optics, one with the
focal plane. The present design of the focal plane foresees, as an auxiliary
instrument, the inclusion of a Polarimeter based on a Micropattern Chamber. We
show how such a device is capable to solve open problems on many classes of
High Energy Astrophysics objects and to use X-ray sources as a laboratory for a
substantial progress on Fundamental Physics.Comment: 12 pages, 7 figure
A prospective cohort study of surgical treatment for back pain with degenerated discs; study protocol
BACKGROUND: The diagnosis of discogenic back pain often leads to spinal fusion surgery and may partly explain the recent rapid increase in lumbar fusion operations in the United States. Little is known about how patients undergoing lumbar fusion compare in preoperative physical and psychological function to patients who have degenerative discs, but receive only non-surgical care. METHODS: Our group is implementing a multi-center prospective cohort study to compare patients with presumed discogenic pain who undergo lumbar fusion with those who have non-surgical care. We identify patients with predominant low back pain lasting at least six months, one or two-level disc degeneration confirmed by imaging, and a normal neurological exam. Patients are classified as surgical or non-surgical based on the treatment they receive during the six months following study enrollment. RESULTS: Three hundred patients discogenic low back pain will be followed in a prospective cohort study for two years. The primary outcome measure is the Modified Roland-Morris Disability Questionnaire at 24-months. We also evaluate several other dimensions of outcome, including pain, functional status, psychological distress, general well-being, and role disability. CONCLUSION: The primary aim of this prospective cohort study is to better define the outcomes of lumbar fusion for discogenic back pain as it is practiced in the United States. We additionally aim to identify characteristics that result in better patient selection for surgery. Potential predictors include demographics, work and disability compensation status, initial symptom severity and duration, imaging results, functional status, and psychological distress
The XMM-Newton serendipitous survey - II. First results from the AXIS high galactic latitude medium sensitivity survey
We present the first results on the identifications of a medium sensitivity survey (X-ray flux limit 2 x 10(-14) erg cm(-2) s(-1) in the 0.5-4.5 keV band) at high galactic latitude (\b\ > 20degrees) carried out with the XMM-Newton X-ray observatory within the AXIS observing programme. This study is being conducted as part of the XMM-Newton Survey Science Centre activities towards the identification of the sources in the X-ray serendipitous sky survey. The sample contains 29 X-ray sources in a solid angle of 0.26 deg(2) (source density 113 +/- 21 sources deg(-2)), out of which 27 (93%) have been identified. The majority of the sources are broad-line AGN (19), followed by narrow emission line X-ray emitting galaxies (6, all of which turn out to be AGN), 1 nearby non-emission line galaxy (NGC 4291) and 1 active coronal star. Among the identified sources we find 2 broad-absorption line QSOs (z similar to 1.8 and z similar to 1.9), which constitute similar to10% of the AGN population at this flux level, similar to optically selected samples. Identifications of a further 10 X-ray sources fainter than our survey limit are also presented
POLARIX: a small mission of x-ray polarimetry
X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber
in the focus of a telescope. It requires large area optics for most important
scientific targets. But since the technique is additive a dedicated mission
with a cluster of small telescopes can perform many important measurements and
bridge the 40 year gap between OSO-8 data and future big telescopes such as
XEUS. POLARIX has been conceived as such a pathfinder. It is a Small Satellite
based on the optics of JET-X. Two telescopes are available in flight
configuration and three more can be easily produced starting from the available
superpolished mandrels. We show the capabilities of such a cluster of
telescopes each equipped with a focal plane photoelectric polarimeter and
discuss a few alternative solutions.Comment: 9 pages, 5 figure
Gravitationally redshifted absorption lines in the X-ray burst spectra of a neutron star
The fundamental properties of neutron stars provide a direct test of the
equation of state of cold nuclear matter, a relationship between pressure and
density that is determined by the physics of the strong interactions between
the particles that constitute the star. The most straightforward method of
determining these properties is by measuring the gravitational redshift of
spectral lines produced in the neutron star photosphere. The equation of state
implies a mass-radius relation, while a measurement of the gravitational
redshift at the surface of a neutron star provides a direct constraint on the
mass-to-radius ratio. Here we report the discovery of signficant absorption
lines in the spectra of 28 bursts of the low-mass X-ray binary EXO 0748-676. We
identify the most signficant features with the Fe XXVI and XXV n=2-3 and O VIII
n=1-2 transitions, all with a redshift of z=0.35, identical within small
uncertainties for the respective transitions. For an astrophysically plausible
range of masses (M ~ 1.3-2.0 M_solar), this value is completely consistent with
models of neutron stars composed of normal nuclear matter, while it excludes
some models in which the neutron stars are made of more exotic matter.Comment: Published in Nature (Nov 7, 2002
- …