199 research outputs found
MGGPOD: a Monte Carlo Suite for Modeling Instrumental Line and Continuum Backgrounds in Gamma-Ray Astronomy
Intense and complex instrumental backgrounds, against which the much smaller
signals from celestial sources have to be discerned, are a notorious problem
for low and intermediate energy gamma-ray astronomy (~50 keV - 10 MeV).
Therefore a detailed qualitative and quantitative understanding of instrumental
line and continuum backgrounds is crucial for most stages of gamma-ray
astronomy missions, ranging from the design and development of new
instrumentation through performance prediction to data reduction. We have
developed MGGPOD, a user-friendly suite of Monte Carlo codes built around the
widely used GEANT (Version 3.21) package, to simulate ab initio the physical
processes relevant for the production of instrumental backgrounds. These
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. The MGGPOD package and documentation are publicly available for
download from http://sigma-2.cesr.fr/spi/MGGPOD/.
We demonstrate the capabilities of the MGGPOD suite by modeling high
resolution gamma-ray spectra recorded by the Transient Gamma-Ray Spectrometer
(TGRS) on board Wind during 1995. The TGRS is a Ge spectrometer operating in
the 40 keV to 8 MeV range. Due to its fine energy resolution, these spectra
reveal the complex instrumental background in formidable detail, particularly
the many prompt and delayed gamma-ray lines. We evaluate the successes and
failures of the MGGPOD package in reproducing TGRS data, and provide
identifications for the numerous instrumental lines.Comment: 60 pages, 13 figures, 7 tables, accepted for publication in ApJ
Integral results on GRB030320: a long gamma-ray burst detected at the edge of the field of view
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
Imaging and burst location with the EXIST high-energy telescope
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
The faint 2005 hard state outburst of Aquila X-1 seen by INTEGRAL and RXTE
We report on the spectral analysis of RXTE and INTEGRAL data of the 2005
April outburst of the transient Atoll source Aql X-1. Although this outburst is
one of the faintest ever detected for this source in the soft X-rays
(RXTE/ASM), one of our INTEGRAL observations, taken close to the soft X-ray
peak, shows that the source flux was quite high, with a 20-200 keV flux of 2.05
x 10^-9 erg cm^-2 s^-1. On this occasion we detect the source up to 150 keV for
the first time. We compare and discuss the similarity of the source behavior
with that of black hole transients especially XTE J1550-564.Comment: 4 pages 2 figures, Accepted for publication in A&A as a RESEARCH NOT
Hard X-ray Emission Clumps in the gamma-Cygni Supernova Remnant: an INTEGRAL-ISGRI View
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 Letter
A Bow Shock Nebula Around a Compact X-Ray Source in the Supernova Remnant IC443
We present spectra and high resolution images of the hard X-ray feature along
the southern edge of the supernova remnant IC443. Data from the Chandra X-ray
Observatory reveal a comet-shaped nebula of hard emission, which contains a
softer point source at its apex. We also present 20cm, 6cm, and 3.5cm images
from the Very Large Array that clearly show the cometary nebula. Based on the
radio and X-ray morphology and spectrum, and the radio polarization properties,
we argue that this object is a synchrotron nebula powered by the compact source
that is physically associated with IC443. The spectrum of the soft point source
is adequately but not uniquely fit by a black body model (kT=0.71 +/- 0.08 keV,
L=(6.5 +/- 0.9) * 10^31 erg/s). The cometary morphology of the nebula is the
result of the supersonic motion of the neutron star (V_NS=250 +/- 50 km/s),
which causes the relativistic wind of the pulsar to terminate in a bow shock
and trail behind as a synchrotron tail. This velocity is consistent with an age
of 30,000 years for the SNR and its associated neutron star.Comment: 9 pages, 5 figures, accepted for publication in the ApJ Letter
The INTEGRAL/SPI response and the Crab observations
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.Comment: 4 pages, 4 figures, Proc. of the 5th INTEGRAL Workshop (Feb. 16-20
2004), to be published by ES
SPI Measurements of Galactic 26Al
The precision measurement of the 1809 keV gamma-ray line from Galactic
Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge
detector camera. We aim for determination of the detailed shape of this
gamma-ray line, and its variation for different source regions along the plane
of the Galaxy. Data from the first part of the core program observations of the
first mission year have been inspected. A clear detection of the \Al line at
about 5--7 significance demonstrates that SPI will deepen \Al studies.
The line intensity is consistent with expectations from previous experiments,
and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more
consistent with RHESSI's recent value. Only preliminary statements can be made
at this time, however, due to the multi-component background underlying the
signal at \about 40 times higher intensity than the signal from Galactic
Al.Comment: 5 pages, 8 figures; accepted for publication in A&A (special INTEGRAL
volume
XTE J1550-564: INTEGRAL Observations of a Failed Outburst
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
outbursts 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 instablility. In that
context, we apply model fitting to derive the timescale for viscous propagation
in the disk, and infer some physical characteristics.Comment: 22 pages, 8 figures, to be published in The Astrophysical Journa
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