229 research outputs found
The Advanced Compton Telescope
The Advanced Compton Telescope (ACT), the next major step in gamma-ray astronomy, will probe the fires where chemical elements are formed by enabling high-resolution spectroscopy of nuclear emission from supernova explosions. During the past two years, our collaboration has been undertaking a NASA mission concept study for ACT. This study was designed to (1) transform the key scientific objectives into specific instrument requirements, (2) to identify the most promising technologies to meet those requirements, and (3) to design a viable mission concept for this instrument. We present the results of this study, including scientific goals and expected performance, mission design, and technology recommendations
SPI/INTEGRAL observation of the Cygnus region
We present the analysis of the first observations of the Cygnus region by the
SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing
600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375
were clearly detected. Our data illustrate the temporal variability of Cyg X-1
in the energy range from 20 keV to 300 keV. The spectral analysis shows a
remarkable stability of the Cyg X-1 spectra when averaged over one day
timescale. The other goal of these observations is SPI inflight calibration and
performance verification. The latest objective has been achieved as
demonstrated by the results presented in this paper.Comment: 6 pages, 10 figures, accepted for publication in A&A (special
INTEGRAL volume
Recommended from our members
HDAC9 is implicated in atherosclerotic aortic calcification and affects vascular smooth muscle cell phenotype.
Aortic calcification is an important independent predictor of future cardiovascular events. We performed a genome-wide association meta-analysis to determine SNPs associated with the extent of abdominal aortic calcification (n = 9,417) or descending thoracic aortic calcification (n = 8,422). Two genetic loci, HDAC9 and RAP1GAP, were associated with abdominal aortic calcification at a genome-wide level (P < 5.0 × 10-8). No SNPs were associated with thoracic aortic calcification at the genome-wide threshold. Increased expression of HDAC9 in human aortic smooth muscle cells promoted calcification and reduced contractility, while inhibition of HDAC9 in human aortic smooth muscle cells inhibited calcification and enhanced cell contractility. In matrix Gla protein-deficient mice, a model of human vascular calcification, mice lacking HDAC9 had a 40% reduction in aortic calcification and improved survival. This translational genomic study identifies the first genetic risk locus associated with calcification of the abdominal aorta and describes a previously unknown role for HDAC9 in the development of vascular calcification
SPI/INTEGRAL in-flight performance
The SPI instrument has been launched on-board the INTEGRAL observatory on
October 17, 2002. SPI is a spectrometer devoted to the sky observation in the
20 keV-8 MeV energy range using 19 germanium detectors. The performance of the
cryogenic system is nominal and allows to cool the 19 kg of germanium down to
85 K with a comfortable margin. The energy resolution of the whole camera is
2.5 keV at 1.1 MeV. This resolution degrades with time due to particle
irradiation in space. We show that the annealing process allows the recovery of
the initial performance. The anticoincidence shield works as expected, with a
low threshold at 75 keV, reducing the GeD background by a factor of 20. The
digital front-end electronics system allows the perfect alignement in time of
all the signals as well as the optimisation of the dead time (12%). We
demonstrate that SPI is able to map regions as complex as the galactic plane.
The obtained spectrum of the Crab nebula validates the present version of our
response matrix. The 3 sensitivity of the instrument at 1 MeV is 8
10phcmskeV for the continuum and 3
10phcms for narrow lines.Comment: 10 pages, 18 figures, accepted for publication in A&A (special
INTEGRAL volume
Calibration of the Spectrometer aboard the INTEGRAL satellite
SPI, the Spectrometer on board the ESA INTEGRAL satellite, to be launched in
October 2002, will study the gamma-ray sky in the 20 keV to 8 MeV energy band
with a spectral resolution of 2 keV for photons of 1 MeV, thanks to its 19
germanium detectors spanning an active area of 500 cm2. A coded mask imaging
technique provides a 2 deg angular resolution. The 16 deg field of view is
defined by an active BGO veto shield, furthermore used for background
rejection. In April 2001 the flight model of SPI underwent a one-month
calibration campaign at CEA in Bruy\`eres le Ch\^atel using low intensity
radioactive sources and the CEA accelerator for homogeneity measurements and
high intensity radioactive sources for imaging performance measurements. After
integration of all scientific payloads (the spectrometer SPI, the imager IBIS
and the monitors JEM-X and OMC) on the INTEGRAL satellite, a cross-calibration
campaign has been performed at the ESA center in Noordwijk. A set of sources
has been placed in the field of view of the different instruments in order to
compare their performances and determine their mutual influence. Some of those
sources had already been used in Bruy\`eres during the SPI standalone test. For
the lowest energy band calibration an X-ray generator has been used. We report
on the scientific goals of this calibration activity, and present the
measurements performed as well as some preliminary results.Comment: 12 pages, 19 figures, Published in Proceedings of SPIE conference,
24-28 August 2002, Waikoloa, Hawaii, US
INTEGRAL/SPI ground calibration
Three calibration campaigns of the spectrometer SPI have been performed
before launch in order to determine the instrument characteristics, such as the
effective detection area, the spectral resolution and the angular resolution.
Absolute determination of the effective area has been obtained from simulations
and measurements. At 1 MeV, the effective area is 65 cm^2 for a point source on
the optical axis, the spectral resolution ~2.3 keV. The angular resolution is
better than 2.5 deg and the source separation capability about 1 deg. Some
temperature dependant parameters will require permanent in-flight calibration.Comment: 9 pages, 12 figures, 2 tables. Accepted for publication in A&AL
(INTEGRAL Special issue
Single-shot diffraction data from the Mimivirus particle using an X-ray free-electron laser
Citation: Ekeberg, T., Svenda, M., Seibert, M. M., Abergel, C., Maia, F. R. N. C., Seltzer, V., . . . Hajdu, J. (2016). Single-shot diffraction data from the Mimivirus particle using an X-ray free-electron laser. Scientific Data, 3. doi:10.1038/sdata.2016.60Free-electron lasers (FEL) hold the potential to revolutionize structural biology by producing X-ray pules short enough to outrun radiation damage, thus allowing imaging of biological samples without the limitation from radiation damage. Thus, a major part of the scientific case for the first FELs was three-dimensional (3D) reconstruction of non-crystalline biological objects. In a recent publication we demonstrated the first 3D reconstruction of a biological object from an X-ray FEL using this technique. The sample was the giant Mimivirus, which is one of the largest known viruses with a diameter of 450 nm. Here we present the dataset used for this successful reconstruction. Data-analysis methods for single-particle imaging at FELs are undergoing heavy development but data collection relies on very limited time available through a highly competitive proposal process. This dataset provides experimental data to the entire community and could boost algorithm development and provide a benchmark dataset for new algorithms
- …