63 research outputs found
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
Influence of the Earth on the background and the sensitivity of the GRM and ECLAIRs instruments aboard the Chinese-French mission SVOM
SVOM (Space-based multi-band astronomical Variable Object Monitor) is a
future Chinese-French satellite mission which is dedicated to Gamma-Ray Burst
(GRB) studies. Its anti-solar pointing strategy makes the Earth cross the field
of view of its payload every orbit. In this paper, we present the variations of
the gamma-ray background of the two high energy instruments aboard SVOM, the
Gamma-Ray Monitor (GRM) and ECLAIRs, as a function of the Earth position. We
conclude with an estimate of the Earth influence on their sensitivity and their
GRB detection capability.Comment: 24 pages, 15 figures, accepted for publication in Experimental
Astronom
Large-Mass Ultra-Low Noise Germanium Detectors: Performance and Applications in Neutrino and Astroparticle Physics
A new type of radiation detector, a p-type modified electrode germanium
diode, is presented. The prototype displays, for the first time, a combination
of features (mass, energy threshold and background expectation) required for a
measurement of coherent neutrino-nucleus scattering in a nuclear reactor
experiment. The device hybridizes the mass and energy resolution of a
conventional HPGe coaxial gamma spectrometer with the low electronic noise and
threshold of a small x-ray semiconductor detector, also displaying an intrinsic
ability to distinguish multiple from single-site particle interactions. The
present performance of the prototype and possible further improvements are
discussed, as well as other applications for this new type of device in
neutrino and astroparticle physics (double-beta decay, neutrino magnetic moment
and WIMP searches).Comment: submitted to Phys. Rev.
SPI/INTEGRAL observation of the Cygnus region
We present the analysis of the first observations of the Cygnus region by the
SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing
600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375
were clearly detected. Our data illustrate the temporal variability of Cyg X-1
in the energy range from 20 keV to 300 keV. The spectral analysis shows a
remarkable stability of the Cyg X-1 spectra when averaged over one day
timescale. The other goal of these observations is SPI inflight calibration and
performance verification. The latest objective has been achieved as
demonstrated by the results presented in this paper.Comment: 6 pages, 10 figures, accepted for publication in A&A (special
INTEGRAL volume
SIGMA Observations of the Bursting Pulsar GRO J1744-28
We present the results of the GRANAT/SIGMA hard X-/soft gamma-ray long-term
monitoring of the Galactic Center (GC) region concerning the source GRO
J1744-28, discovered on 1995 Dec. 2 by CGRO/BATSE. SIGMA observed the region
containing the source in 14 opportunities between 1990 and 1997. In two of
these observing sessions, corresponding to March 1996 and March 1997, GRO
J1744-28 was detected with a confidence level greater than 5(sigma) in the
35-75 keV energy band without detection in the 75-150 keV energy band. For the
other sessions, upper limits of the flux are indicated. The particular imaging
capabilities of the SIGMA telescope allow us to identify, specifically, the
source position in the very crowded GC region, giving us a mean flux of (73.1
+/- 5.5)E-11 and (44.7 +/- 6.4)E-11 ergs cm^-2 s^-1 in the 35-75 keV energy
band, for the March 1996 and March 1997 observing sessions, respectively.
Combining the March 1997 SIGMA and BATSE observations, we found evidence
pointing to the type-II nature of the source bursts for this period. For the
same observing campaigns, spectra were obtained in the 35 to 150 keV energy
band. The best fit corresponds to an optically thin thermal Bremsstrahlung with
F(50 keV)=(3.6 +/- 0.6)E-4 phot cm^-2 s^-1 keV^-1 and kT(Bremss)=28 +/- 7 keV,
for the first campaign, and F(50 keV)=(2.3 +/- 0.7)E-4 phot cm^-2 s^-1 keV^-1
and kT(Bremss)=18 (+12/-7) keV, for the second. This kind of soft spectrum is
typical of binary sources containing a neutron star as the compact object, in
contrast to the harder spectra typical of systems containing a black hole
candidateComment: Accepted for publication in the Astrophysical Journal, 4 pages, 4
figure
The INTEGRAL Galactic bulge monitoring program: the first 1.5 years
The Galactic bulge region is a rich host of variable high-energy point
sources. Since 2005, February 17 we are monitoring the source activity in this
region about every three days with INTEGRAL. Thanks to the large field of view,
the imaging capabilities and the sensitivity at hard X-rays, we are able to
present for the first time a detailed homogeneous (hard) X-ray view of a sample
of 76 sources in the Galactic bulge region. We describe the successful
monitoring program and show the first results for a period of about one and a
half year. We focus on the short (hour), medium (month) and long-term (year)
variability in the 20-60 keV and 60-150 keV bands. When available, we discuss
the simultaneous observations in the 3-10 keV and 10-25 keV bands. Per
visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources
in the 60-150 keV band. On average, we find per visibility season one active
bright (>~100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three
active weaker (<~25 mCrab, 20-60 keV) neutron star X-ray transients. Most of
the time a clear anti-correlation can be seen between the soft and hard X-ray
emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray
bursters, which have a duration of the order of weeks, are accompanied by soft
X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft
X-ray flares/outbursts. We found a number of new sources, IGR J17354-3255, IGR
17453-2853, IGR J17454-2703, IGR J17456-2901b, IGR J17536-2339, and IGR
J17541-2252. We report here on some of the high-energy properties of these
sources. The high-energy light curves of all the sources in the field of view,
and the high-energy images of the region, are made available through the WWW at
http://isdc.unige.ch/Science/BULGE/.Comment: 27 pages, 42 figures, accepted for publication in A&A. Abstract
abridged. Tables 3,4,6,7 appear at the end. Images have been compressed and
are reduced in quality; original PostScript images can be retrieved from
http://isdc.unige.ch/~kuulkers/bulge
Hard X-ray sky survey with the SIGMA telescope aboard GRANAT observatory
During the lifetime of GRANAT orbital observatory the SIGMA telescope
collected X-ray images of more than 1/4 of the whole sky. Among these regions
the Galactic Center had largest exposure time (~9 million sec). In the present
work we review all observations of the SIGMA telescope and present
sensitivities achieved with it at different sky regionsComment: 6 pages, 5 figures. Accepted for publication in Astronomy Letter
Hard X-ray emission from the Galactic ridge
We present results of a study of the Galactic ridge X-ray emission (GRXE) in
hard X-rays performed with the IBIS telescope aboard INTEGRAL. The imaging
capabilities of this coding aperture telescope make it possible to account for
the flux from bright Galactic point sources whereas the wide field of view
permits to collect large flux from the underlying GRXE. Extensive study of the
IBIS/ISGRI detector background allowed us to construct a model that predicts
the detector count rate with % accuracy in the energy band 17-60 keV.
The derived longitude and latitude profiles of the ridge emission are in good
agreement with the Galactic distribution of stars obtained from infrared
observations. This, along with the measured hard X-ray spectrum of the Galactic
ridge emission strongly indicates its stellar origin. The derived unit stellar
mass emissivity of the ridge in the energy band 17-60 keV, \lummass (assuming a bulge mass of )
agrees with that of local (in the Solar neigborhood) accreting magnetic white
dwarf binaries - dominant contributors to the GRXE at these energies. In
addition, the shape of the obtained GRXE spectrum can be used to determine the
average mass of white dwarfs in such systems in the Galaxy as \sim0.5
M_{\sun}. The total hard X-ray luminosity of the GRXE is \lum in the 17--60 keV band. At energies 70--200 keV
no additional contribution to the total emission of the Galaxy apart from the
detected point sources is seen.Comment: 13 pages, 19 figures, submitted to Astronomy and Astrophysic
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