223 research outputs found
Monte-Carlo simulations of the background of the coded-mask camera for X- and Gamma-rays on-board the Chinese-French GRB mission SVOM
For several decades now, wide-field coded mask cameras have been used with
success to localise Gamma-ray bursts (GRBs). In these instruments, the event
count rate is dominated by the photon background due to their large field of
view and large effective area. It is therefore essential to estimate the
instrument background expected in orbit during the early phases of the
instrument design in order to optimise the scientific performances of the
mission. We present here a detailed study of the instrument background and
sensitivity of the coded-mask camera for X- and Gamma-rays (CXG) to be used in
the detection and localisation of high-redshift GRBs on-board the international
GRB mission SVOM. To compute the background spectrum, a Monte-Carlo approach
was used to simulate the primary and secondary interactions between particles
from the main components of the space environment that SVOM will encounter
along its Low Earth Orbit (LEO) (with an altitude of 600 km and an inclination
of ~ 30 deg) and the body of the CXG. We consider the detailed mass model of
the CXG in its latest design. According to our results, i) the design of the
passive shield of the camera ensures that in the 4-50 keV imaging band the
cosmic X-Gamma-ray background is dominant whilst the internal background should
start to become dominant above 70-90 keV; ii) the current camera design ensures
that the CXG camera will be more sensitive to high-redshift GRBs than the Swift
Burst Alert Telescope thanks to a low-energy threshold of 4 keV.Comment: 16 pages, 10 figures (1 colour), accepted for publication in Nuclear
Instruments and Methods in Physics Research: Section
Continuum gamma-ray emission from light dark matter positrons and electrons
The annihilation of light dark matter was recently advocated as a possible
explanation of the large positron injection rate at the Galactic center deduced
from observations by the SPI spectrometer aboard INTEGRAL. The modelling of
internal Bremsstrahlung and in-flight annihilation radiations associated to
this process drastically reduced the mass range of this light dark matter
particle. We estimate critically the various energy losses and radiations
involved in the propagation of the positron before its annihilation --in-
flight or at rest.
Using a simple model with mono-energetic positrons injected and confined to
the Galactic bulge, we compute energy losses and gamma-ray radiations caused by
ionization, Bremsstrahlung interactions as well as in-flight and at rest
annihilation and compare these predictions to the available observations, for
various injection energies.
Confronting the predictions with observations by the CGRO/EGRET,
CGRO/COMPTEL, INTEGRAL/SPI and INTEGRAL/IBIS/ISGRI instruments, we deduce a
mass upper bound of 3 to 7.5 MeV/c^2 for the hypothetical light dark matter
particle. The most restrictive limit is in agreement with the value previously
found by Beacom and Yuksel and was obtained under similar assumptions, while
the 7.5 MeV/c^2 value corresponds to more conservative choices and to a
partially ionized propagation medium. We stress how the limit depends on the
degree of ionization of the propagation medium and how its precision could be
improved by a better appraisal of data uncertainties.Comment: Revision of the section dedicated to the observational
interpretation. 11 pages, 8 figures, 1 table. Accepted for publication in
Phys. Rev.
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
INTEGRAL broadband spectroscopy of Vela X-1
The wind-accreting X-ray binary pulsar and cyclotron line source Vela X-1 has
been observed extensively during INTEGRAL Core Program observations of the Vela
region in June-July and November-December 2003. In the latter set of
observations the source showed intense flaring -- see also Staubert et al.
(2004), these proceedings.
We present early results on time averaged and time resolved spectra, of both
epochs of observations. A cyclotron line feature at ~53 keV is clearly detected
in the INTEGRAL spectra and its broad shape is resolved in SPI spectra. The
remaining issues in the calibration of the instruments do not allow to resolve
the question of the disputed line feature at 20-25 keV.
During the first main flare the average luminosity increases by a factor of
\~10, but the spectral shape remains very similar, except for a moderate
softening.Comment: Accepted for proceedings of 5th INTEGRAL Worksho
The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM
The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low
Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based
multi-band astronomical Variable Objects Monitor), a French-Chinese mission
with Italian contribution. Observations are expected to start in 2013. It has
been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent
sources of the sky, thanks to its wide field of view (about 2 sr) and its
remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging
sensitivity in the 4-70 keV energy band. These characteristics are well suited
to detect highly redshifted GRBs, and consequently to provide fast and accurate
triggers to other onboard or ground-based instruments able to follow-up the
detected events in a very short time from the optical wavelength bands up to
the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008,
Nanjing, Chin
A Hard X-ray View on Scorpius X-1 with INTEGRAL: non-Thermal Emission ?
We present here simultaneous INTEGRAL/RXTE observations of Sco X-1, and in
particular a study of the hard X-ray emission of the source and its correlation
with the position in the Z-track of the X-ray color-color diagram. We find that
the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a
power-law component with a photon index of ~3. The flux in the power-law
component slightly decreases when the source moves in the color-color diagram
in the sense of increasing inferred mass accretion rate from the horizontal
branch to the normal branch/flaring branch vertex. It becomes not significantly
detectable in the flaring branch, where its flux has decreased by about an
order of magnitude. These results present close analogies to the behavior of GX
17+2, one of so-called Sco-like Z sources. Finally, the hard power law in the
spectrum of Sco X-1 does not show any evidence of a high energy cutoff up to
100 - 200 keV, strongly suggesting a non-thermal origin of this component.Comment: 5 pages including 3 figures. Accepted for publication by ApJ Letter
Fault-controlled and stratabound dolostones in the Late Aptian-earliest Albian Benassal Formation (Maestrat Basin, E Spain) : petrology and geochemistry constrains
This study was developed under the ExxonMobil FC2 Alliance (Fundamental Controls on Flow in Carbonates). The authors wish to thank ExxonMobil Production Company and ExxonMobil Upstream Research Company for providing funding. The views in this article by Sherry L. Stafford are her own and not necessarily those of ExxonMobil. This research was supported by the Sedimentary Geology Research Group of the Generalitat de Catalunya (2014SGR251). We would like to thank Andrea Ceriani and Paola Ronchi for their critical and valuable reviews, and Associated Editor Piero Gianolla for the editorial work.Peer reviewedPostprin
Measurement of 1.7 to 74 MeV polarised gamma rays with the HARPO TPC
Current {\gamma}-ray telescopes based on photon conversions to
electron-positron pairs, such as Fermi, use tungsten converters. They suffer of
limited angular resolution at low energies, and their sensitivity drops below 1
GeV. The low multiple scattering in a gaseous detector gives access to higher
angular resolution in the MeV-GeV range, and to the linear polarisation of the
photons through the azimuthal angle of the electron-positron pair.
HARPO is an R&D program to characterise the operation of a TPC (Time
Projection Chamber) as a high angular-resolution and sensitivity telescope and
polarimeter for {\gamma} rays from cosmic sources. It represents a first step
towards a future space instrument. A 30 cm cubic TPC demonstrator was built,
and filled with 2 bar argon-based gas. It was put in a polarised {\gamma}-ray
beam at the NewSUBARU accelerator in Japan in November 2014. Data were taken at
different photon energies from 1.7 MeV to 74 MeV, and with different
polarisation configurations. The electronics setup is described, with an
emphasis on the trigger system. The event reconstruction algorithm is quickly
described, and preliminary measurements of the polarisation of 11 MeVphotons
are shown.Comment: Proceedings VCI201
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