1,772 research outputs found
Polarized Gamma-ray Emission from the Galactic Black Hole Cygnus X-1
Because of their inherently high flux allowing the detection of clear
signals, black hole X-ray binaries are interesting candidates for polarization
studies, even if no polarization signals have been observed from them before.
Such measurements would provide further detailed insight into these sources'
emission mechanisms. We measured the polarization of the gamma-ray emission
from the black hole binary system Cygnus X-1 with the INTEGRAL/IBIS telescope.
Spectral modeling of the data reveals two emission mechanisms: The 250-400 keV
data are consistent with emission dominated by Compton scattering on thermal
electrons and are weakly polarized. The second spectral component seen in the
400keV-2MeV band is by contrast strongly polarized, revealing that the MeV
emission is probably related to the jet first detected in the radio band.Comment: 11 pages, 3 figures, to be published in Science in April 22nd 2011,
available on Science Express Web site (March 24th edition
Optical-to-optical interface device
An investigation was conducted to develop an optical-to-optical interface device capable of performing real-time incoherent-to-incoherent optical image conversion. The photoactivated liquid crystal light valve developed earlier represented a prototype liquid crystal light valve device capable of performing these functions. A device was developed which had high performance and extended lifetime
Variability in high-mass X-ray binaries
Strongly magnetized, accreting neutron stars show periodic and aperiodic
variability over a wide range of time scales. By obtaining spectral and timing
information on these different time scales, we can have a closer look into the
physics of accretion close to the neutron star and the properties of the
accreted material. One of the most prominent time scales is the strong
pulsation, i.e., the rotation period of the neutron star itself. Over one
rotation, our view of the accretion column and the X-ray producing region
changes significantly. This allows us to sample different physical conditions
within the column but at the same time requires that we have
viewing-angle-resolved models to properly describe them. In wind-fed high-mass
X-ray binaries, the main source of aperiodic variability is the clumpy stellar
wind, which leads to changes in the accretion rate (i.e., luminosity) as well
as absorption column. This variability allows us to study the behavior of the
accretion column as a function of luminosity, as well as to investigate the
structure and physical properties of the wind, which we can compare to winds in
isolated stars.Comment: 6 pages, 4 figures, accepted for publication in Astronomische
Nachrichten (proceedings of the XMM-Newton Workshop 2019
Spectral state dependence of the 0.4-2 MeV polarized emission in Cygnus X-1 seen with INTEGRAL/IBIS, and links with the AMI radio data
Polarization of the >~400 keV hard tail of the microquasar Cygnus X-1 has
been independently reported by INTEGRAL/IBIS, and INTEGRAL/SPI and interpreted
as emission from a compact jet. These conclusions were, however, based on the
accumulation of all INTEGRAL data regardless of the spectral state. We utilize
additional INTEGRAL exposure accumulated until December 2012, and include the
AMI/Ryle (15 GHz) radio data in our study. We separate the observations into
hard, soft, and intermediate/transitional states and detect radio emission from
a compact jet in hard and intermediate states, but not in the soft. The 10-400
keV INTEGRAL (JEM-X and IBIS) state resolved spectra are well modeled with
thermal Comptonization and reflection components. We detect a hard tail in the
0.4-2 MeV range for the hard state only. We extract the state dependent
polarigrams of Cyg X-1, which all are compatible to no or undetectable level of
polarization except in 400-2000 keV range in the hard state where the
polarization fraction is 7532 % and the polarization angle 40.0 +-14 deg.
An upper limit on the 0.4-2 MeV soft state polarization fraction is 70%. Due to
the short exposure, we obtain no meaningful constraint for the intermediate
state. The likely detection of a >400 keV polarized tail in the hard state,
together with the simultaneous presence of a radio jet, reinforce the notion of
a compact jet origin of the 400 keV emission.Comment: 13 pages, 5 figures, accepted for publication in Ap
The SMC SNR 1E0102.2-7219 as a Calibration Standard for X-ray Astronomy in the 0.3-2.5 keV Bandpass
The flight calibration of the spectral response of CCD instruments below 1.5
keV is difficult in general because of the lack of strong lines in the on-board
calibration sources typically available. We have been using 1E 0102.2-7219, the
brightest supernova remnant in the Small Magellanic Cloud, to evaluate the
response models of the ACIS CCDs on the Chandra X-ray Observatory (CXO), the
EPIC CCDs on the XMM-Newton Observatory, the XIS CCDs on the Suzaku
Observatory, and the XRT CCD on the Swift Observatory. E0102 has strong lines
of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the
spectrum. The spectrum of E0102 has been well characterized using
high-resolution grating instruments, namely the XMM-Newton RGS and the CXO
HETG, through which a consistent spectral model has been developed that can
then be used to fit the lower-resolution CCD spectra. We have also used the
measured intensities of the lines to investigate the consistency of the
effective area models for the various instruments around the bright O (~570 eV
and 654 eV) and Ne (~910 eV and 1022 eV) lines. We find that the measured
fluxes of the O VII triplet, the O VIII Ly-alpha line, the Ne IX triplet, and
the Ne X Ly-alpha line generally agree to within +/-10 % for all instruments,
with 28 of our 32 fitted normalizations within +/-10% of the RGS-determined
value. The maximum discrepancies, computed as the percentage difference between
the lowest and highest normalization for any instrument pair, are 23% for the O
VII triplet, 24% for the O VIII Ly-alpha line, 13% for the Ne IX triplet, and
19% for the Ne X Ly-alpha line. If only the CXO and XMM are compared, the
maximum discrepancies are 22% for the O VII triplet, 16% for the O VIII
Ly-alpha line, 4% for the Ne IX triplet, and 12% for the Ne X Ly-alpha line.Comment: 16 pages, 11 figures, to be published in Proceedings of the SPIE
7011: Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray 200
L-Drawings of Directed Graphs
We introduce L-drawings, a novel paradigm for representing directed graphs
aiming at combining the readability features of orthogonal drawings with the
expressive power of matrix representations. In an L-drawing, vertices have
exclusive - and -coordinates and edges consist of two segments, one
exiting the source vertically and one entering the destination horizontally.
We study the problem of computing L-drawings using minimum ink. We prove its
NP-completeness and provide a heuristics based on a polynomial-time algorithm
that adds a vertex to a drawing using the minimum additional ink. We performed
an experimental analysis of the heuristics which confirms its effectiveness.Comment: 11 pages, 7 figure
Vela X-1 as a laboratory for accretion in High-Mass X-ray Binaries
Vela X-1 is an eclipsing high mass X-ray binary (HMXB) consisting of a 283s
accreting X-ray pulsar in a close orbit of 8.964 days around the B0.5Ib
supergiant HD77581 at a distance of just 2.4 kpc. The system is considered a
prototype of wind-accreting HMXB and it has been used as a baseline in
different theoretical or modelling studies.
We discuss the observational properties of the system and the use of the
observational data as laboratory to test recent developments in modelling the
accretion process in High-Mass X-ray Binaries (e.g., Sander et al. 2018; El
Mellah et al. 2018), which range from detailed descriptions of the wind
acceleration to modelling of the structure of the flow of matter close to the
neutron star and its variations.Comment: 4 pages, 2 figures, proceedings of the 12th INTEGRAL conference
"INTEGRAL looks AHEAD to Multimessenger astronomy" in Geneva (Switzerland) on
11-15 February 201
Mutations in the EXT1 and EXT2 genes in Spanish patients with multiple osteochondromas
Multiple osteochondromas is an autosomal dominant skeletal disorder characterized by the formation of multiple cartilage-capped tumours. Two causal genes have been identified, EXT1 and EXT2, which account for 65% and 30% of cases, respectively. We have undertaken a mutation analysis of the EXT1 and EXT2 genes in 39 unrelated Spanish patients, most of them with moderate phenotype, and looked for genotype-phenotype correlations. We found the mutant allele in 37 patients, 29 in EXT1 and 8 in EXT2. Five of the EXT1 mutations were deletions identified by MLPA. Two cases of mosaicism were documented. We detected a lower number of exostoses in patients with missense mutation versus other kinds of mutations. In conclusion, we found a mutation in EXT1 or in EXT2 in 95% of the Spanish patients. Eighteen of the mutations were novel.Fil: Sarrión, P.. Universidad de Barcelona; EspañaFil: Sangorrin, A.. Hospital Sant Joan de Déu; EspañaFil: Urreizti, R.. Universidad de Barcelona; EspañaFil: Delgado, María Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba; ArgentinaFil: Artuch, R.. Hospital Sant Joan de Déu; EspañaFil: Martorell, L.. Hospital Sant Joan de Déu; EspañaFil: Armstrong, J.. Hospital Sant Joan de Déu; EspañaFil: Anton, J.. Hospital Sant Joan de Déu; EspañaFil: Torner, F.. Hospital Sant Joan de Déu; EspañaFil: Vilaseca, M. A.. Hospital Sant Joan de Déu; EspañaFil: Nevado, J.. Hospital Universitario La Paz; EspañaFil: Lapunzina, P.. Hospital Universitario La Paz; EspañaFil: Asteggiano, Carla Gabriela. Universidad Nacional de Córdoba; Argentina. Universidad Católica de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Balcells, S.. Universidad de Barcelona; EspañaFil: Grinberg, D.. Universidad de Barcelona; Españ
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