107 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
SPI Measurements of the Diffuse Galactic Hard X-ray Continuum
INTEGRAL Spectrometer SPI data from the first year of the Galactic Centre
Deep Exposure has been analysed for the diffuse continuum from the Galactic
ridge. A new catalogue of sources from the INTEGRAL Imager IBIS has been used
to account for their contribution to the celestial signal. Apparently diffuse
emission is detected at a level ~10% of the total source flux. A comparison of
the spectrum of diffuse emission with that from an analysis of IBIS data alone
shows that they are consistent. The question of the contribution of unresolved
sources to this ridge emission is still open.Comment: Proceedings of the 5th INTEGRAL Workshop, Munich 16-20 February 2004.
ESA SP-552. Reference to Terrier et al. (2004) updated to include astro-ph
versio
Early SPI/INTEGRAL contraints on the morphology of the 511 keV line emission in the 4th galactic quadrant
We provide first constraints on the morphology of the 511 keV line emission
from the galactic centre region on basis of data taken with the spectrometer
SPI on the INTEGRAL gamma-ray observatory. The data suggest an azimuthally
symmetric galactic bulge component with FWHM of ~9 deg with a 2 sigma
uncertainty range covering 6-18 deg. The 511 keV line flux in the bulge
component amounts to (9.9+4.7-2.1) 10e-4 ph cm-2 s-1. No evidence for a
galactic disk component has been found so far; upper 2 sigma flux limits in the
range (1.4-3.4) 10e-3 ph cm-2 s-1 have been obtained that depend on the assumed
disk morphology. These limits correspond to lower limits on the bulge-to-disk
ratio of 0.3-0.6.Comment: 5 pages, 3 figures, accepted for publication in A&
The Crab pulsar light curve in the soft gamma ray range: FIGARO II results
The FIGARO II experiment (a large area, balloon borne, crystal scintillator detector working from 0.15 to 4.3 MeV) observed the Crab pulsar on 1990 Jul. 9 for about seven hours. The study of the pulse profile confirms some structures detected with a low significance during the shorter observation of 1986, and adds new important elements to the picture. In particular, between the two main peaks, two secondary peaks appear centered at phase values 0.1 and 0.3, in the energy range 0.38 to 0.49 MeV; in the same energy range, a spectral feature at 0.44 MeV, interpreted as a redshifted positron annihilation line, was observed during the same balloon flight in the phase interval including the second main peak and the neighboring secondary peak. If the phase interval considered is extended to include also the other secondary peak, the significance of the spectral line appears to increase
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
Long-term Multi-wavelength Observations of GRS 1758-258 and the ADAF Model
We present a long-term multi-wavelength light curve of Galactic black hole
candidate GRS 1758-258 by combining previously published and archival data from
GRANAT, ROSAT, CGRO, RXTE, SAX, ASCA, EXOSAT, and the VLA. In addition we
include first spectral results from the balloon-borne Gamma-ray Arcminute
Telescope Imaging System (GRATIS). In light of divergent analyses of the
1991-1993 ROSAT observations, we have re-analyzed these data; we find the soft
X-rays track the hard X-rays, and that the fits require no black-body
component-- indicating that GRS 1758-258 did not go to the high state in 1993.
We offer an interpretation based on the ADAF model for a system with mdot
\ltsim mdot_crit. We find the 1990-1993 coeval hard and soft X-ray observations
support the ADAF predictions. We discuss a new way to constrain black-hole mass
with spectral data and the ADAF theory, and apply this technique to GRS
1758-258 to find M_1 \gtsim 8--9 M_sol at an assumed distance of 8.5 kpc.
Further investigations of the ADAF model allow us to evaluate the model
critically against the data and flux-flux diagram of Barret, McClintock &
Grindlay (1996) and to understand the limits of the latter's ``X-ray burster
box.''Comment: 32 pp., AASTEX, 8 ps figures, accepted to Ap
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