96 research outputs found
A versatile facility for the calibration of X-ray polarimeters with polarized and unpolarized controlled beams
We devised and built a versatile facility for the calibration of the next
generation X-ray polarimeters with unpolarized and polarized radiation. The
former is produced at 5.9 keV by means of a Fe55 radioactive source or by X-ray
tubes, while the latter is obtained by Bragg diffraction at nearly 45 degrees.
Crystals tuned with the emission lines of X-ray tubes with molybdenum, rhodium,
calcium and titanium anodes are employed for the efficient production of highly
polarized photons at 2.29, 2.69, 3.69 and 4.51 keV respectively. Moreover the
continuum emission is exploited for the production of polarized photons at 1.65
keV and 2.04 keV and at energies corresponding to the higher orders of
diffraction. The photons are collimated by means of interchangeable capillary
plates and diaphragms, allowing a trade-off between collimation and high
fluxes. The direction of the beam is accurately arranged by means of high
precision motorized stages, controlled via computer so that long and automatic
measurements can be done. Selecting the direction of polarization and the
incidence point we can map the response of imaging devices to both polarized
and unpolarized radiation. Changing the inclination of the beam we can study
the systematic effects due to the focusing of grazing incidence optics and the
feasibility of instruments with large field of view.Comment: 12 pages, 11 figure
Measurement of the position resolution of the Gas Pixel Detector
The Gas Pixel Detector was designed and built as a focal plane instrument for
X-ray polarimetry of celestial sources, the last unexplored subtopics of X-ray
astronomy. It promises to perform detailed and sensitive measurements resolving
extended sources and detecting polarization in faint sources in crowded fields
at the focus of telescopes of good angular resolution. Its polarimetric and
spectral capability were already studied in earlier works. Here we investigate
for the first time, with both laboratory measurements and Monte Carlo
simulations, its imaging properties to confirm its unique capability to carry
out imaging spectral-polarimetry in future X-ray missions.Comment: Submitted to Nuclear Instruments and Methods in Physics Research
Section A; 15 figures, 3 table
IXPE Mission System Concept and Development Status
The Goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mi SMEX), is to expand understanding of high-energy astrophysical processes and sources, in support of NASAs first science objective in Astrophysics: Discover how the universe works. IXPE, an international collaboration, will conduct X-ray imaging polarimetry for multiple categories of cosmic X-ray sources such as neutron stars, stellar-mass black holes, supernova remnants and active galactic nuclei. The Observatory uses a single science operational mode capturing the X-ray data from the targets. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three X-ray telescopes each consisting of a polarization-sensitive, gas pixel X-ray detector, paired with its corresponding grazing incidence mirror module assembly (MMA). A deployable boom provides the correct separation (focal length) between the detector units (DU) and MMAs. These payload elements are supported by the IXPE spacecraft which is derived from the BCP-small spacecraft architecture. This paper summarizes the IXPE mission science objectives, updates the Observatory implementation concept including the payload and spacecraft ts and summarizes the mission status since last years conference
LAMP: a micro-satellite based soft X-ray polarimeter for astrophysics
The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite
mission concept dedicated for astronomical X-ray polarimetry and is currently
under early phase study. It consists of segmented paraboloidal multilayer
mirrors with a collecting area of about 1300 cm^2 to reflect and focus 250 eV
X-rays, which will be detected by position sensitive detectors at the focal
plane. The primary targets of LAMP include the thermal emission from the
surface of pulsars and synchrotron emission produced by relativistic jets in
blazars. With the expected sensitivity, it will allow us to detect polarization
or place a tight upper limit for about 10 pulsars and 20 blazars. In addition
to measuring magnetic structures in these objects, LAMP will also enable us to
discover bare quark stars if they exist, whose thermal emission is expected to
be zero polarized, while the thermal emission from neutron stars is believed to
be highly polarized due to plasma polarization and the quantum electrodynamics
(QED) effect. Here we present an overview of the mission concept, its science
objectives and simulated observational results
Re-testing the JET-X Flight Module No. 2 at the PANTER facility
The Joint European X-ray Telescope (JET-X) was the core instrument of the
Russian Spectrum-X-gamma space observatory. It consisted of two identical soft
X-ray (0.3 - 10 keV) telescopes with focusing optical modules having a measured
angular resolution of nearly 15 arcsec. Soon after the payload completion, the
mission was cancelled and the two optical flight modules (FM) were brought to
the Brera Astronomical Observatory where they had been manufactured. After 16
years of storage, we have utilized the JET-X FM2 to test at the PANTER X-ray
facility a prototype of a novel X-ray polarimetric telescope, using a Gas Pixel
Detector (GPD) with polarimetric capabilities in the focal plane of the FM2.
The GPD was developed by a collaboration between INFN-Pisa and INAF-IAPS. In
the first phase of the test campaign, we have re-tested the FM2 at PANTER to
have an up-to-date characterization in terms of angular resolution and
effective area, while in the second part of the test the GPD has been placed in
the focal plane of the FM2. In this paper we report the results of the tests of
the sole FM2, using an unpolarized X-ray source, comparing the results with the
calibration done in 1996.Comment: Author's accepted manuscript posted to arXiv.org as permitted by
Springer's Self-Archiving Policy. The final publication is available at
http://rd.springer.com/article/10.1007%2Fs10686-013-9365-
The Gas Pixel Detector as an X-ray photoelectric polarimeter with a large field of view
The Gas Pixel Detector (GPD) is a new generation device which, thanks to its
50 um pixels, is capable of imaging the photoelectrons tracks produced by
photoelectric absorption in a gas. Since the direction of emission of the
photoelectrons is strongly correlated with the direction of polarization of the
absorbed photons, this device has been proposed as a polarimeter for the study
of astrophysical sources, with a sensitivity far higher than the instruments
flown to date. The GPD has been always regarded as a focal plane instrument and
then it has been proposed to be included on the next generation space-borne
missions together with a grazing incidence optics. Instead in this paper we
explore the feasibility of a new kind of application of the GPD and of the
photoelectric polarimeters in general, i.e. an instrument with a large field of
view. By means of an analytical treatment and measurements, we verify if it is
possible to preserve the sensitivity to the polarization for inclined beams,
opening the way for the measurement of X-ray polarization for transient
astrophysical sources. While severe systematic effects arise for inclination
greater than about 20 degrees, methods and algorithms to control them are
discussed.Comment: 11 pages, 8 figure
PolarLight: a CubeSat X-ray Polarimeter based on the Gas Pixel Detector
The gas pixel detector (GPD) is designed and developed for high-sensitivity
astronomical X-ray polarimetry, which is a new window about to open in a few
years. Due to the small mass, low power, and compact geometry of the GPD, we
propose a CubeSat mission Polarimeter Light (PolarLight) to demonstrate and
test the technology directly in space. There is no optics but a collimator to
constrain the field of view to 2.3 degrees. Filled with pure dimethyl ether
(DME) at 0.8 atm and sealed by a beryllium window of 100 micron thick, with a
sensitive area of about 1.4 mm by 1.4 mm, PolarLight allows us to observe the
brightest X-ray sources on the sky, with a count rate of, e.g., ~0.2 counts/s
from the Crab nebula. The PolarLight is 1U in size and mounted in a 6U CubeSat,
which was launched into a low Earth Sun-synchronous orbit on October 29, 2018,
and is currently under test. More launches with improved designs are planned in
2019. These tests will help increase the technology readiness for future
missions such as the enhanced X-ray Timing and Polarimetry (eXTP), better
understand the orbital background, and may help constrain the physics with
observations of the brightest objects.Comment: Accepted for publication in Experimental Astronom
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
Enalapril reduces proliferation and hyaluronic acid release in orbital fibroblasts
BACKGROUND:
Orbital fibroblast proliferation and hyaluronic acid (HA) release are responsible for some of the clinical features of Graves' ophthalmopathy (GO). Thus, inhibition of these processes may be a possible therapeutic approach to this syndrome. Enalapril, a widely used antihypertensive drug, was found to have some inhibitory actions on fibroblast proliferation in cheloid scars in vivo, based on which we investigated its effects in primary cultures of orbital fibroblasts from GO patients and control subjects.
METHODS:
Primary cultures of GO and control fibroblasts were treated with enalapril or with a control compound (lisinopril). Cell proliferation assays, lactate dehydrogenase release assays (as a measure of cell necrosis), apoptosis assays, and measurement of HA in the cell media were performed.
RESULTS:
Enalapril significantly reduced cell proliferation in both GO and control fibroblasts. Because enalapril did not affect cell necrosis and apoptosis, we concluded that its effects on proliferation reflected an inhibition of cell growth and/or a delay in cell cycle. Enalapril significantly reduced HA concentrations in the media from both GO and control fibroblasts.
CONCLUSIONS:
Enalapril has antiproliferative and HA suppressing actions in both GO and control fibroblasts. Clinical studies are needed to investigate whether enalapril has any effects in vivo in patients with GO
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