388 research outputs found
Hyper-velocity impact test and simulation of a double-wall shield concept for the Wide Field Monitor aboard LOFT
The space mission LOFT (Large Observatory For X-ray Timing) was selected in
2011 by ESA as one of the candidates for the M3 launch opportunity. LOFT is
equipped with two instruments, the Large Area Detector (LAD) and the Wide Field
Monitor (WFM), based on Silicon Drift Detectors (SDDs). In orbit, they would be
exposed to hyper-velocity impacts by environmental dust particles, which might
alter the surface properties of the SDDs. In order to assess the risk posed by
these events, we performed simulations in ESABASE2 and laboratory tests. Tests
on SDD prototypes aimed at verifying to what extent the structural damages
produced by impacts affect the SDD functionality have been performed at the Van
de Graaff dust accelerator at the Max Planck Institute for Nuclear Physics
(MPIK) in Heidelberg. For the WFM, where we expect a rate of risky impacts
notably higher than for the LAD, we designed, simulated and successfully tested
at the plasma accelerator at the Technical University in Munich (TUM) a
double-wall shielding configuration based on thin foils of Kapton and
Polypropylene. In this paper we summarize all the assessment, focussing on the
experimental test campaign at TUM.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
Simulations of the X-ray imaging capabilities of the Silicon Drift Detectors (SDD) for the LOFT Wide Field Monitor
The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the
four Cosmic Vision M3 candidate missions to undergo an assessment phase, will
revolutionize the study of compact objects in our galaxy and of the brightest
supermassive black holes in active galactic nuclei. The Large Area Detector
(LAD), carrying an unprecedented effective area of 10 m^2, is complemented by a
coded-mask Wide Field Monitor, in charge of monitoring a large fraction of the
sky potentially accessible to the LAD, to provide the history and context for
the sources observed by LAD and to trigger its observations on their most
interesting and extreme states. In this paper we present detailed simulations
of the imaging capabilities of the Silicon Drift Detectors developed for the
LOFT Wide Field Monitor detection plane. The simulations explore a large
parameter space for both the detector design and the environmental conditions,
allowing us to optimize the detector characteristics and demonstrating the
X-ray imaging performance of the large-area SDDs in the 2-50 keV energy band.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-210, 201
A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL
In this Letter we present results from INTEGRAL and RXTE observations of the
spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its
August/September 2005 normal (type I) outburst with an average flux
F(5-100keV)~400mCrab. The search for cyclotron resonance scattering features
(fundamental and harmonic) is one major focus of the paper. Our analysis is
based on data from INTEGRAL and RXTE Target of Opportunity Observations
performed during the outburst. The pulse period is determined. X-ray pulse
profiles in different energy ranges are analyzed. The broad band INTEGRAL and
RXTE pulse phase averaged X-ray spectra are studied. The evolution of the
fundamental cyclotron line at different luminosities is analyzed. The pulse
period P is measured to be 103.39315(5)s at MJD 53614.5137. Two absorption
features are detected in the phase averaged spectra at E_1~45keV and
E_2~100keV. These can be interpreted as the fundamental cyclotron resonance
scattering feature and its first harmonic and therefore the magnetic field can
be estimated to be B~4x10^12G.Comment: 4 pages, 5 figures, accepted for publication in A&A Letter
Combined iPLEX and TaqMan assays to screen for 45 common mutations in Lynch syndrome and FAP patients
Detection of Active Caspase-3 in Mouse Models of Stroke and Alzheimer\u27s Disease with a Novel Dual Positron Emission Tomography/Fluorescent Tracer [68Ga]Ga-TC3-OGDOTA.
Apoptosis is a feature of stroke and Alzheimer\u27s disease (AD), yet there is no accepted method to detect or follow apoptosis in the brain in vivo. We developed a bifunctional tracer [Ga-68]Ga-TC3-OGDOTA containing a cell-penetrating peptide separated from fluorescent Oregon Green and Ga-68-bound labels by the caspase-3 recognition peptide DEVD. We hypothesized that this design would allow [Ga-68]Ga-TC3-OGDOTA to accumulate in apoptotic cells. In vitro, Ga-TC3-OGDOTA labeled apoptotic neurons following exposure to camptothecin, oxygen-glucose deprivation, and -amyloid oligomers. In vivo, PET showed accumulation of [Ga-68]Ga-TC3-OGDOTA in the brain of mouse models of stroke or AD. Optical clearing revealed colocalization of [Ga-68]Ga-TC3-OGDOTA and cleaved caspase-3 in brain cells. In stroke, [Ga-68]Ga-TC3-OGDOTA accumulated in neurons in the penumbra area, whereas in AD mice [Ga-68]Ga-TC3-OGDOTA was found in single cells in the forebrain and diffusely around amyloid plaques. In summary, this bifunctional tracer is selectively associated with apoptotic cells in vitro and in vivo in brain disease models and represents a novel tool for apoptosis detection that can be used in neurodegenerative diseases
Spectro-timing analysis of Cygnus X-1 during a fast state transition
We present the analysis of two long, quasi-uninterrupted RXTE observations of
Cygnus X-1 that span several days within a 10 d interval. The spectral
characteristics during this observation cover the region where previous
observations have shown the source to be most dynamic. Despite that the source
behavior on time scales of hours and days is remarkably similar to that on year
time scales. This includes a variety of spectral/temporal correlations that
previously had only been observed over Cyg X-1's long-term evolution.
Furthermore, we observe a full transition from a hard to a soft spectral state
that occurs within less than 2.5 hours - shorter than previously reported for
any other similar Cyg X-1 transition. We describe the spectra with a
phenomenological model dominated by a broken power law, and we fit the X-ray
variability power spectra with a combination of a cutoff power law and
Lorentzian components. The spectral and timing properties are correlated: the
power spectrum Lorentzian components have an energy-dependent amplitude, and
their peak frequencies increase with photon spectral index. Averaged over
3.2-10 Hz, the time lag between the variability in the 4.5-5.7 keV and 9.5-15
keV bands increases with decreasing hardness when the variability is dominated
by the Lorentzian components during the hard state. The lag is small when there
is a large power law noise contribution, shortly after the transition to the
soft state. Interestingly, the soft state not only shows the shortest lags, but
also the longest lags when the spectrum is at its softest and faintest. We
discuss our results in terms of emission models for black hole binaries.Comment: 13 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Detection of active caspase-3 in mouse models of stroke and Alzheimer\u27s disease with a novel dual positron emission tomography/fluorescent tracer [ \u3csup\u3e68\u3c/sup\u3e Ga]Ga-TC3-OGDOTA
© 2019 Valeriy G. Ostapchenko et al. Apoptosis is a feature of stroke and Alzheimer\u27s disease (AD), yet there is no accepted method to detect or follow apoptosis in the brain in vivo. We developed a bifunctional tracer [ 68 Ga]Ga-TC3-OGDOTA containing a cell-penetrating peptide separated from fluorescent Oregon Green and 68 Ga-bound labels by the caspase-3 recognition peptide DEVD. We hypothesized that this design would allow [ 68 Ga]Ga-TC3-OGDOTA to accumulate in apoptotic cells. In vitro, Ga-TC3-OGDOTA labeled apoptotic neurons following exposure to camptothecin, oxygen-glucose deprivation, and β-amyloid oligomers. In vivo, PET showed accumulation of [ 68 Ga]Ga-TC3-OGDOTA in the brain of mouse models of stroke or AD. Optical clearing revealed colocalization of [ 68 Ga]Ga-TC3-OGDOTA and cleaved caspase-3 in brain cells. In stroke, [ 68 Ga]Ga-TC3-OGDOTA accumulated in neurons in the penumbra area, whereas in AD mice [ 68 Ga]Ga-TC3-OGDOTA was found in single cells in the forebrain and diffusely around amyloid plaques. In summary, this bifunctional tracer is selectively associated with apoptotic cells in vitro and in vivo in brain disease models and represents a novel tool for apoptosis detection that can be used in neurodegenerative diseases
The relative and absolute timing accuracy of the EPIC-pn camera on XMM-Newton, from X-ray pulsations of the Crab and other pulsars
Reliable timing calibration is essential for the accurate comparison of
XMM-Newton light curves with those from other observatories, to ultimately use
them to derive precise physical quantities. The XMM-Newton timing calibration
is based on pulsar analysis. However, as pulsars show both timing noise and
glitches, it is essential to monitor these calibration sources regularly. To
this end, the XMM-Newton observatory performs observations twice a year of the
Crab pulsar to monitor the absolute timing accuracy of the EPIC-pn camera in
the fast Timing and Burst modes. We present the results of this monitoring
campaign, comparing XMM-Newton data from the Crab pulsar (PSR B0531+21) with
radio measurements. In addition, we use five pulsars (PSR J0537-69, PSR
B0540-69, PSR B0833-45, PSR B1509-58 and PSR B1055-52) with periods ranging
from 16 ms to 197 ms to verify the relative timing accuracy. We analysed 38
XMM-Newton observations (0.2-12.0 keV) of the Crab taken over the first ten
years of the mission and 13 observations from the five complementary pulsars.
All the data were processed with the SAS, the XMM-Newton Scientific Analysis
Software, version 9.0. Epoch folding techniques coupled with \chi^{2} tests
were used to derive relative timing accuracies. The absolute timing accuracy
was determined using the Crab data and comparing the time shift between the
main X-ray and radio peaks in the phase folded light curves. The relative
timing accuracy of XMM-Newton is found to be better than 10^{-8}. The strongest
X-ray pulse peak precedes the corresponding radio peak by 306\pm9 \mus, which
is in agreement with other high energy observatories such as Chandra, INTEGRAL
and RXTE. The derived absolute timing accuracy from our analysis is \pm48 \mus.Comment: 16 pages, 9 figures. Accepted for publication on A&
Pulse phase resolved analysis of the HMXB Cen X-3 over two binary orbits
We present a detailed analysis of observations of the high mass X-ray binary
Cen X-3 spanning two consecutive binary orbits performed with the RXTE
satellite in early March 1997. The PCA and HEXTE light curves both show a clear
reduction in count rate after mid-orbit for both binary revolutions. We
therefore analyze two broad band spectra for each orbit, before and after
mid-orbit. Consistent with earlier observations these four joint PCA and HEXTE
spectra can be well described using a phenomenological pulsar continuum model,
including an iron emission line and a cyclotron resonance scattering feature.
While no strong spectral variations were detected, the second half of orbit 2
shows a tendency toward being softer and more strongly absorbed. In order to
follow the orbital phase-dependent evolution of the spectrum in greater detail,
we model spectra for shorter exposures, confirming that most spectral
parameters show either a gradual or sudden change for the second half of the
second orbit. A comparison with a simple wind model indicates the existence of
an accretion wake in this system. We also present and discuss high resolution
pulse profiles for several different energy bands, as well as their hardness
ratios. PCA and HEXTE spectra were created for 24 phase bins and fitted using
the same model as in the phase averaged case. Systematic pulse phase-dependent
variations of several continuum and cyclotron line parameters were detected,
most notably a significant increase of the cyclotron line energy during the
early rise of the main peak, followed by a gradual decrease. We show that
applying a simple dipole model for the magnetic field is not sufficient to
describe our data.Comment: 12 pages, 9 figures, accepted for publication in Ap
A Suzaku View of Cyclotron Line Sources and Candidates
Seventeen accreting neutron star pulsars, mostly high mass X-ray binaries
with half of them Be-type transients, are known to exhibit Cyclotron Resonance
Scattering Features (CRSFs) in their X-ray spectra, with characteristic line
energies from 10 to 60 keV. To date about two thirds of them, plus a few
similar systems without known CRSFs, have been observed with Suzaku. We present
an overview of results from these observations, including the discovery of a
CRSF in the transient 1A 1118-61 and pulse phase resolved spectroscopy of GX
301-2. These observations allow for the determination of cyclotron line
parameters to an unprecedented degree of accuracy within a moderate amount of
observing time. This is important since these parameters vary - e.g., with
orbital phase, pulse phase, or luminosity - depending on the geometry of the
magnetic field of the pulsar and the properties of the accretion column at the
magnetic poles. We briefly introduce a spectral model for CRSFs that is
currently being developed and that for the first time is based on these
physical properties. In addition to cyclotron line measurements, selected
highlights from the Suzaku analyses include dip and flare studies, e.g., of 4U
1907+09 and Vela X-1, which show clumpy wind effects (like partial absorption
and/or a decrease in the mass accretion rate supplied by the wind) and may also
display magnetospheric gating effects.Comment: 8 pages, 5 figures, 1 table, to appear in the proceedings of the
conference "Suzaku 2011 Exploring the X-ray Universe: Suzaku and Beyond"
which will be published electronically by AI
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