318 research outputs found
Low-energy gamma rays from Cygnus X-1
The Cyg X-1 was observed by the balloonborne telescope OPALE, in June 1976. The high energy spectrum of the source, which was in its superlow state, was seen to extend well beyond 1 MeV. The observed low energy gamma ray component of Cyg X-1 is compared with the predictions of recent models involving accretion onto a stellar black hole, and including a possible contribution from the pair annihilation 511 keV gamma ray line
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
Le 27 juin 1995
Je m'étais rendue, sans grand enthousiasme, je l'avoue, à la discrète cérémonie du 27 juin 1995 qui devait marquer la cession des papiers personnels de mon mari, le professeur Robert Mandrou, aux Archives nationales, par l'intermédiaire du Centre de recherches historiques de l'École des hautes études en sciences sociales, manifestation tout à fait représentative, par sa modestie et son atmosphère chaleureuse, des rapports qu'entretenait l'École avec Robert Mandrou. Et un doute persistant, qua..
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