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ABSTRACT: The primary instrument of the proposed EXIST mission is a coded mask high energy telescope (the HET), that must have a wide field of view and extremely good sensitivity. It will be crucial to minimize systematic errors so that even for very long total integration times the imaging performance is close to the statistical photon limit. There is also a requirement to be able to reconstruct images on-board in near real time in order to detect and localize gamma-ray bursts. This must be done while the spacecraft is scanning the sky. The scanning provides all-sky coverage and is key to reducing systematic errors. The on-board computational problem is made even more challenging for EXIST by the very large number of detector pixels. Numerous alternative designs for the HET have been evaluated. The baseline concept adopted depends on a unique coded mask with two spatial scales. Monte Carlo simulations and analytic analysis techniques have been used to demonstrate the capabilities of the design and of the proposed two-step burst localization procedure.
02/2010;
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ABSTRACT: The baseline concept for the primary instrument of the EXIST mission,
the high energy telescope (HET), is a coded mask instrument with a wide
field of view and extremely good sensitivity (Hong et al., this
meeting). Achieving the performance goals requires an imaging capability
close to the statistical photon limit, minimizing systematic errors even
when the total integration time is very long. At the same time there is
a requirement to be able to reconstruct images on board in near real
time in order to detect and localize gamma-ray bursts. This must be done
while the spacecraft is scanning the sky with a motion designed to help
reduce systematic errors and to provide all-sky coverage. During the
2008 Advanced Mission Concept Study, the Exist Imaging Technical Working
Group has investigated and compared numerous alternative designs for the
HET. The selected baseline concept meets all of the scientific
requirements, while being compatible with spacecraft and launch
constraints and with those imposed by the Infra-Red Telescope that forms
the other key part of the mission. The approach adopted depends on a
unique annular coded mask with two spatial scales, offering good
resolution and low background at low energies, with a lower resolution
but enhanced sensitivity in the upper part of the energy band. Monte
Carlo simulations and analytic analysis techniques have been used to
demonstrate the capabilities of the proposed design.
12/2008; 41:349.
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ABSTRACT: We announce the forthcoming public release of Version 1.1 of MGGPOD, a user-friendly suite of Monte Carlo codes built around the widely used GEANT (Version 3.21) package. MGGPOD is capable of simulating ab initio the physical processes relevant for the production of instrumental backgrounds. These processes include the build-up and delayed decay of radioactive isotopes as well as the prompt de-excitation of excited nuclei, both of which give rise to a plethora of instrumental gamma-ray background lines in addition to continuum backgrounds. A detailed qualitative and quantitative understanding of instrumental backgrounds is crucial for most stages of high-energy astronomy missions. Improvements implemented in Version 1.1 of the proven MGGPOD Monte Carlo suite include: additional beam geometry options, the capability of modelling polarized photons, additional output formats suitable e.g. for event reconstruction algorithms, improved neutron interaction cross sections, and improved treatment of the radioactive decay of isomeric nuclear states. The MGGPOD package and documentation are publicly available for download from http://sigma-2.cesr.fr/spi/MGGPOD/.
03/2007;
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A. M. Bykov,
A. M. Krassilchtchikov,
Yu. A. Uvarov,
H. Bloemen,
R. A. Chevalier,
M. Yu. Gustov,
W. Hermsen,
F. Lebrun,
T. A. Lozinskaya,
G. Rauw,
T. V. Smirnova, S. J. Sturner,
J. -P. Swings,
R. Terrier,
I. N. Toptygin
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ABSTRACT: Spatially resolved images of the galactic supernova remnant G78.2+2.1 (gamma-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The images are dominated by localized clumps of about ten arcmin in size. The flux of the most prominent North-Western (NW) clump is (1.7 +/- 0.4) 10^{-11} erg/cm^2/s in the 25-40 keV band. The observed X-ray fluxes are in agreement with extrapolations of soft X-ray imaging observations of gamma-Cygni by ASCA GIS and spatially unresolved RXTE PCA data. The positions of the hard X-ray clumps correlate with bright patches of optical line emission, possibly indicating the presence of radiative shock waves in a shocked cloud. The observed spatial structure and spectra are consistent with model predictions of hard X-ray emission from nonthermal electrons accelerated by a radiative shock in a supernova interacting with an interstellar cloud, but the powerful stellar wind of the O9V star HD 193322 is a plausible candidate for the NW source as well. Comment: 5 pages, 5 figures, Astronomy and Astrophysics Letters
10/2004;
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P. Sizun,
C. R. Shrader,
D. Attie,
P. Dubath,
S. Schanne,
B. Cordier, S. J. Sturner,
L. Bouchet,
J. P. Roques,
G. K. Skinner,
P. Connell
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ABSTRACT: The Crab region was observed several times by INTEGRAL for calibration purposes. This paper aims at underlining the systematic interactions between (i) observations of this reference source, (ii) in-flight calibration of the instrumental response and (iii) the development and validation of the analysis tools of the SPI spectrometer. It first describes the way the response is produced and how studies of the Crab spectrum lead to improvements and corrections in the initial response. Then, we present the tools which were developed to extract spectra from the SPI observation data and finally a Crab spectrum obtained with one of these methods, to show the agreement with previous experiments. We conclude with the work still ahead to understand residual uncertainties in the response.
07/2004;
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ABSTRACT: We present the initial results from our study of the nonthermal continuum emission from the supernova remnants Cassiopeia A, MSB 11-61-4, a d CT-4 1. We used the INTEGRAL Core Program data to conduct this study. During the INTEGRAL mission a significant fraction of the total observing time (e.g. 35% in year one) is allocated to the Core Program and is analyzed under the auspices of the INTEGRAL Science Working Team. We report no statistically significant detections thus far but we will continue to analyze the data as more is taken. The results so far are consistent with previous measurements from e.g. RXTE and ASCA.
02/2004;
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ABSTRACT: The well known black-hole X-ray binary transient XTE J1550-564 underwent an outburst during the spring of 2003 which was substantially underluminous in comparison to previous periods of peak activity in that source. In addition, our analysis shows that it apparently remained in the hard spectral state over the duration of that outburst. This is again in sharp contrast to major out-bursts of that source in 1998/1999 during which it exhibited an irregular light curve, multiple state changes and collimated outflows. This leads us to classify it as a failed outburst. We present the results of our study of the spring 2003 event including light curves based on observations from both INTEGRAL and RXTE. In addition, we studied the evolution of the high-energy 3-300 keV continuum spectrum using data obtained with three main instruments on INTEGRAL. These spectra are consistent with typical low-hard-state thermal Comptonization emission. We also consider the 2003 event in the context of a multi-source, multi-event period-peak luminosity diagram in which it is a clear outlyer. We then consider the possibility that the 2003 event was due to a discrete accretion event rather than a limit-cycle instability. In that context, apply model fitting to derive the timescale for viscous propagation in the disk, and infer some physical characteristics.
02/2004;
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A. von Kienlin,
V. Beckmann,
S. Covino,
D. Goetz,
G. G. Lichti,
D. Malesani,
S. Mereghetti,
E Molinari,
A. Rau,
C. R. Shrader, S. J. Sturner,
F. Zerbi
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ABSTRACT: GRB030320 is the 5th Gamma-ray burst (GRB) detected by INTEGRAL in the field of view (FoV). It is so far the GRB with the largest off-axis angle with respect to the INTEGRAL pointing direction, near to the edge of the FoV of both main instruments, IBIS and SPI. Nevertheless, it was possible to determine its position and to extract spectra and fluxes. The GRB nature of the event was confirmed by an IPN triangulation. It is a ~ 60 s long GRB with two prominent peaks separated by ~ 35 s. The spectral shape of the GRB is best represented by a single power law with a photon index Gamma ~ 1.7. The peak flux in the 20 - 200 keV band is determined to ~ 5.7 photons cm-2 s-1 and the GRB fluence to 1.1 x 10-5 erg cm-2. Analysing the spectral evolution of the GRB, a ``hard-to-soft'' behaviour emerges. A search for an optical counterpart has been carried out, but none was found. Comment: 5 pages, 3 figures. Accepted for publication in A&AL (INTEGRAL issue)
08/2003;
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ABSTRACT: In this paper we discuss the methods developed for the production of the INTEGRAL/SPI instrument response. The response files were produced using a suite of Monte Carlo simulation software developed at NASA/GSFC based on the GEANT-3 package available from CERN. The production of the INTEGRAL/SPI instrument response also required the development of a detailed computer mass model for SPI. We discuss our extensive investigations into methods to reduce both the computation time and storage requirements for the SPI response. We also discuss corrections to the simulated response based on our comparison of ground and inflight calibration data with MGEANT simulation.
02/2003;
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ABSTRACT: MGEANT is a multi-purpose simulation package based on the CERN GEANT package and Program Library. This package allows for the rapid prototyping of a wide variety of gamma-ray detector systems. The two main advantages of this package over standard GEANT simulations are 1) the detector geometry and material data are supplied via input files instead of being hard coded and 2) MGEANT has several built in spectral and beam options including the ability to simulate observations with multiple pointings and diffuse sources. We are currently using MGEANT to produce detailed observation simulations and response matrices for INTEGRAL/SPI. We present a sample of the type of work that has been done at GSFC using MGEANT simulations. This software package is available from our website http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/integral/. © 2000 American Institute of Physics.
AIP Conference Proceedings. 04/2000; 510(1):814-818.
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ABSTRACT: The SPI gamma-ray spectrometer on INTEGRAL is a coded mask spectrometer
with 19 germanium detectors, which will offer high spectral resolution
together with the capability of imaging both point and extended sources.
To study the performance of the instrument, both a Monte Carlo model,
based on MGEANT developed at NASA/GSFC, and ray-tracing techniques,
developed at U. Birmingham, are being used to produce simulated data.
These data are processed with imaging software which is a prototype of
the software to be used in flight. The imaging procedures use a variety
of constrained matrix and spline techniques. We show preliminary results
for reconstructions of the diffuse Galactic 511 keV annihilation
radiation and the 1809 keV emission from the decay of (26) Al. We also
show a reconstruction of five bright point sources within +/-5 degrees
of the Galactic Center.
11/1997; 29:1300.
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A. von Kienlin,
V. Beckmann,
S. Covino,
D. Götz,
G. G. Lichti,
D. Malesani,
S. Mereghetti,
E Molinari,
A. Rau,
C. R. Shrader, S. J. Sturner,
F. Zerbi
Astronomy & Astrophysics, v.411, L321-L325 (2003).
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S. J. Sturner,
C. R. Shrader,
G. Weidenspointner,
B. J. Teegarden,
D. Attié,
B. Cordier,
R. Diehl,
C. Ferguson,
P. Jean,
A. von Kienlin,
Ph. Paul,
F Sánchez,
S. Schanne,
P. Sizun,
G. Skinner,
C. B. Wunderer
Astronomy & Astrophysics, v.411, L81-L84 (2003).
