323 research outputs found
The digital data processing concepts of the LOFT mission
The Large Observatory for X-ray Timing (LOFT) is one of the five mission
candidates that were considered by ESA for an M3 mission (with a launch
opportunity in 2022 - 2024). LOFT features two instruments: the Large Area
Detector (LAD) and the Wide Field Monitor (WFM). The LAD is a 10 m 2 -class
instrument with approximately 15 times the collecting area of the largest
timing mission so far (RXTE) for the first time combined with CCD-class
spectral resolution. The WFM will continuously monitor the sky and recognise
changes in source states, detect transient and bursting phenomena and will
allow the mission to respond to this. Observing the brightest X-ray sources
with the effective area of the LAD leads to enormous data rates that need to be
processed on several levels, filtered and compressed in real-time already on
board. The WFM data processing on the other hand puts rather low constraints on
the data rate but requires algorithms to find the photon interaction location
on the detector and then to deconvolve the detector image in order to obtain
the sky coordinates of observed transient sources. In the following, we want to
give an overview of the data handling concepts that were developed during the
study phase.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
Peculiar outburst of A 0535+26 observed with INTEGRAL, RXTE and Suzaku
A normal outburst of the Be/X-ray binary system A0535+26 has taken place in
August 2009. It is the fourth in a series of normal outbursts that have occured
around the periastron passage of the source, but is unusual by starting at an
earlier orbital phase and by presenting a peculiar double-peaked light curve. A
first "flare" (lasting about 9 days from MJD 55043 on) reached a flux of 440
mCrab. The flux then decreased to less than 220 mCrab, and increased again
reaching 440 mCrab around the periastron at MJD 55057. Target of Opportunity
observations have been performed with INTEGRAL, RXTE and Suzaku. First results
of these observations are presented, with special emphasis on the cyclotron
lines present in the X-ray spectrum of the source, as well as in the pulse
period and energy dependent pulse profiles of the source.Comment: 6 pages, Accepted for publication on PoS, Proceedings of "The Extreme
sky: Sampling the Universe above 10 keV", held in Otranto (Italy) in October
200
RXTE Discovery of Multiple Cyclotron Lines during the 2004 December Outburst of V0332+53
We present an analysis of the 2-150 keV spectrum of the transient X-ray
pulsar V0332+53 taken with the Rossi X-Ray Timing Explorer (RXTE) in 2004
December. We report on the detection of three cyclotron resonance features at
27, 51, and 74 keV in the phase-averaged data, corresponding to a polar
magnetic field of 2.7 x 10^12 G. After 4U0115+63, this makes V0332+53 the
second accreting neutron star in which more than two cyclotron lines have been
detected; this has now also been confirmed by INTEGRAL. Pulse-phase
spectroscopy reveals remarkably little variability of the cyclotron line
through the 4.4 s X-ray pulse.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
A Double-peaked Outburst of A 0535+26 Observed with INTEGRAL, RXTE, and Suzaku
The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in 2009 August. It is the fourth in a series of normal outbursts associated with the periastron, but is unusual because it presented a double-peaked light curve. The two peaks reached a flux of ~450 mCrab in the 15-50 keV range. We present results of the timing and spectral analysis of INTEGRAL, RXTE, and Suzaku observations of the outburst. The energy-dependent pulse profiles and their evolution during the outburst are studied. No significant differences with respect to other normal outbursts are observed. The centroid energy of the fundamental cyclotron line shows no significant variation during the outburst. A spectral hardening with increasing luminosity is observed. We conclude that the source is accreting in the sub-critical regime. We discuss possible explanations for the double-peaked outburst
Possible Detection of an Emission Cyclotron Resonance Scattering Feature from the Accretion-powered Pulsar 4U 1626-67
We present analysis of 4U 1626-67, a 7.7 s pulsar in a low-mass X-ray binary
system, observed with the hard X-ray detector of the Japanese X-ray satellite
Suzaku in March 2006 for a net exposure of \sim88 ks. The source was detected
at an average 10-60 keV flux of \sim4 x10^-10 erg cm^-2 s^-1. The
phase-averaged spectrum is reproduced well by combining a negative and positive
power-law times exponential cutoff (NPEX) model modified at \sim 37 keV by a
cyclotron resonance scattering feature (CRSF). The phase-resolved analysis
shows that the spectra at the bright phases are well fit by the NPEX with CRSF
model. On the other hand, the spectrum in the dim phase lacks the NPEX
high-energy cutoff component, and the CRSF can be reproduced by either an
emission or an absorption profile. When fitting the dim phase spectrum with the
NPEX plus Gaussian model, we find that the feature is better described in terms
of an emission rather than an absorption profile. The statistical significance
of this result, evaluated by means of an F-test, is between 2.91 x 10^-3 and
1.53 x 10^-5, taking into account the systematic errors in the background
evaluation of HXD-PIN. We find that, the emission profile is more feasible than
the absorption one for comparing the physical parameters in other phases.
Therefore, we have possibly detected an emission line at the cyclotron
resonance energy in the dim phase.Comment: Accepted for publication in ApJ on March 16, 2012. 12 pages, 14
figure
The Be/X-ray binary A0535+26 during its recent 2009/2010 outbursts
The Be/X-ray binary A0535+26 showed a giant outburst in December 2009 that
reached ~5.14 Crab in the 15-50 keV range. Unfortunately, due to Sun
constraints it could not be observed by most X-ray satellites. The outburst was
preceded by four weaker outbursts associated with the periastron passage of the
neutron star. The fourth of them, in August 2009, presented a peculiar
double-peaked light curve, with a first peak lasting about 9 days that reached
a (15-50 keV) flux of 440 mCrab. The flux then decreased to less than 220
mCrab, and increased again reaching 440 Crab around the periastron. The
outburst was monitored with INTEGRAL, RXTE, and Suzaku TOO observations. One
orbital period (~111 days) after the 2009 giant outburst, a new and
unexpectedly bright outburst took place (~1.4Crab in the 15-50 keV range). It
was monitored with TOO obs ervations with INTEGRAL, RXTE, Suzaku, and Swift.
First results of the spectral and timing analysis of these observations are
presented, with a specific focus on the cyclotron lines present in the system
and its variation with the mass accretion rate.Comment: Accepted for publication in Proceedings of Science, 8th INTEGRAL
Workshop, The Restless Gamma-ray Universe, 27-30 September 2010, Dublin,
Irelan
Optimisation of the design for the LOFT Large Area Detector Module
LOFT (Large Observatory for X-ray Timing) is an X-ray timing observatory
that, with four other candidates, was considered by ESA as an M3 mission (with
launch in 2022-2024) and has been studied during an extensive assessment phase.
Its pointed instrument is the Large Area Detector (LAD), a 10 m 2 -class
instrument operating in the 2-30 keV range, which is designed to perform X-ray
timing of compact objects with unprecedented resolution down to millisecond
time scales. Although LOFT was not downselected for launch, during the
assessment most of the trade-offs have been closed, leading to a robust and
well documented design that will be reproposed in future ESA calls. The
building block of the LAD instrument is the Module, and in this paper we
summarize the rationale for the module concept, the characteristics of the
module and the trade-offs/optimisations which have led to the current design.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
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
Inflammatory response gene polymorphisms and their relationship with colorectal cancer risk
<p>Abstract</p> <p>Backgroud</p> <p>Patients with chronic inflammatory bowel disease (IBD) are at an increased risk of colorectal cancer (CRC) and it is estimated that one in six persons diagnosed with IBD will develop CRC. This fact suggests that genetic variations in inflammatory response genes may act as CRC disease risk modifiers.</p> <p>Methods</p> <p>In order to test this hypothesis we investigated a series of polymorphisms in 6 genes (NOD2, DLG5, OCTN1, OCTN2, IL4, TNFα) associated with the inflammatory response on a group of 607 consecutive newly diagnosed colorectal cancer patients and compared the results to controls (350 consecutive newborns and 607 age, sex and geographically matched controls).</p> <p>Results</p> <p>Of the six genes only one polymorphism in TNFα(-1031T/T) showed any tendency to be associated with disease risk (64.9% for controls and 71.4% for CRC) which we further characterized on a larger cohort of CRC patients and found a more profound relationship between the TNFα -1031T/T genotype and disease (64.5% for controls vs 74.7% for CRC cases above 70 yrs). Then, we investigated this result and identified a suggestive tendency, linking the TNFα -1031T/T genotype and a previously identified change in the CARD15/NOD2 gene (OR = 1.87; p = 0,02 for CRC cases above 60 yrs).</p> <p>Conclusion</p> <p>The association of polymorphisms in genes involved in the inflammatory response and CRC onset suggest that there are genetic changes capable of influencing disease risk in older persons.</p
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