40 research outputs found
Broad band spectral properties of Seyfert 1 galaxies observed with BeppoSAX
We will present some results on the broad--band observations of BeppoSAX of
the bright Seyfert galaxies NGC 4151 and NGC 5548.Comment: 5 pages, 4 figures, Proc. of the 32 COSPAR Ass., Session E1.1 "Broad
Band X-Ray Spectra of Cosmic Sources, ed.s K. Makishima, L. Piro, T.
Takahashi, Advances in Space Research, in pres
BeppoSAX Observations of the Radio Galaxy Centaurus A
We present preliminary results from two observations of the radio galaxy
Centaurus A performed by the BeppoSAX satellite. We did not detect any spectral
variation of the nuclear continuum in spite of the long-term flux change (by a
factor 1.3) between the two observations. At both epochs, the nuclear
point-like emission was well fitted with a strongly absorbed power law with an
exponential cutoff at high energies (E_cutoff>200 keV). We also observed a
significant flux variation of the iron line between the two observations. The
flux of the line and of the continuum changed in the opposite sense. The line
is more intense at the first epoch, when the nuclear source was at the lower
intensity level. The implied delay between the continuum and line variations
strongly suggests that the cold material responsible for the iron line
production is not located very near to the primary X-ray source. There is also
evidence that the line profile changed between the two epochs, being broader
and slightly blueshifted when the source was fainter. It is possible that the
emission feature is a blend of cold and ionized iron lines produced in separate
regions surrounding the nuclear source.Comment: 4 pages, 4 figures, accepted for publication in Advances in Space
Research, proceedings of 32nd COSPAR Symposium (1998
The BeppoSAX view of the hard X-ray background
First results on a medium-deep X-ray survey in the "new" 5-10 keV band
carried out with the MECS detectors onboard BeppoSAX are presented. The High
Energy Llarge Area Survey (HELLAS) is aimed to directly explore a band where
the energy density of the X-ray background is more than twice than that in the
soft (0.5-2.0 keV) band. The optical identification follow-up of the first ten
HELLAS hard X-ray sources indicate that Active Galactic Nuclei are the dominant
population at 5-10 keV fluxes of the order of 10e-13 cgs. We discuss the
implications of these findings for the AGN synthesis models for the XRB.Comment: 6 pages, 4 figures, uses psfig.sty. Accepted for publication in
Advances in Space Research, Proceedings of the 32nd Scientific Assembly of
COSPA
Prospects in space-based Gamma-Ray Astronomy
With the unequalled INTEGRAL observatory, ESA has provided a unique tool to
the astronomical community that has made Europe the world leader in the field
of gamma-ray astronomy. INTEGRAL provides an unprecedented survey of the soft
gamma-ray sky, revealing hundreds of sources of different kinds, new classes of
objects, extraordinary views of antimatter annihilation in our Galaxy, and
fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the
longly awaited global overview over the soft gamma-ray sky, there is a growing
need to perform deeper, more focused investigations of gamma-ray sources,
comparable to the step that has been taken in X-rays by going from the ROSAT
survey satellite to the more focused XMM-Newton observatory. Technological
advances in the past years in the domain of gamma-ray focusing using Laue
diffraction techniques have paved the way towards a future European gamma-ray
mission, that will outreach past missions by large factors in sensitivity and
angular resolution. Such a future Gamma-Ray Imager will allow to study particle
acceleration processes and explosion physics in unprecedented depth, providing
essential clues on the intimate nature of the most violent and most energetic
processes in the Universe.Comment: 8 pages, 7 figures, to be published in the Proceedings of the 39th
ESLAB Symposiu
Progress on the development of the Stellar X-ray Polarimeter on board of the Spectrum-X-Gamma Satellite
We present the status of the Stellar X-ray Polarimeter at November’94 devoted to measure linear polarisation from cosmic X-ray sources between 2 keV and 15 keV which will be flown on the Spectrum-X-Gamma Satellite. In particular, we
focus on the performances of the engineering model after the calibrations at Lawrence Livermore Laboratories and on the improvements which have been introduced on the four flight model imaging proportional counters which are key
parts of the experiment
On the nature of X-ray absorption in Seyfert 2 galaxies
We have studied the correlation among X-ray absorption, optical reddening and
nuclear dust morphology in Seyfert 2 galaxies. Two main conclusions emerge: a)
the Balmer decrement and the amount of X-ray absorption are anticorrelated on a
wide range of column density: 10^{21} < N_H < 10^{24} atoms/cm/cm. The
correlation does no longer apply to Compton-thick objects (N_H < 10^{24}
atoms/cm/cm), although they span a comparable range in Balmer decrement; b)
Compton-thin Seyfert 2s seem to prefer nuclear environments, which are rich of
dust on scales of the hundreds parsecs. On the other hand, Compton-thick
Seyferts exhibit indifferently ``dust-poor'' and ``dust-rich'' environments.
These results support an extension of the Seyfert unification scenario (as
recently proposed by Matt, 2000), where Compton-thick Seyfert 2s are observed
through compact ``torii'', whereas Compton-thin ones are obscured by dust on
much larger scalesComment: 7 Latex pages, 6 figures, Accepted for publication in Monthly Notices
of the Royal Astonomical Societ
FTO genetic variants, dietary intake and body mass index: insights from 177,330 individuals.
FTO is the strongest known genetic susceptibility locus for obesity. Experimental studies in animals suggest the potential roles of FTO in regulating food intake. The interactive relation among FTO variants, dietary intake and body mass index (BMI) is complex and results from previous often small-scale studies in humans are highly inconsistent. We performed large-scale analyses based on data from 177,330 adults (154 439 Whites, 5776 African Americans and 17 115 Asians) from 40 studies to examine: (i) the association between the FTO-rs9939609 variant (or a proxy single-nucleotide polymorphism) and total energy and macronutrient intake and (ii) the interaction between the FTO variant and dietary intake on BMI. The minor allele (A-allele) of the FTO-rs9939609 variant was associated with higher BMI in Whites (effect per allele = 0.34 [0.31, 0.37] kg/m(2), P = 1.9 × 10(-105)), and all participants (0.30 [0.30, 0.35] kg/m(2), P = 3.6 × 10(-107)). The BMI-increasing allele of the FTO variant showed a significant association with higher dietary protein intake (effect per allele = 0.08 [0.06, 0.10] %, P = 2.4 × 10(-16)), and relative weak associations with lower total energy intake (-6.4 [-10.1, -2.6] kcal/day, P = 0.001) and lower dietary carbohydrate intake (-0.07 [-0.11, -0.02] %, P = 0.004). The associations with protein (P = 7.5 × 10(-9)) and total energy (P = 0.002) were attenuated but remained significant after adjustment for BMI. We did not find significant interactions between the FTO variant and dietary intake of total energy, protein, carbohydrate or fat on BMI. Our findings suggest a positive association between the BMI-increasing allele of FTO variant and higher dietary protein intake and offer insight into potential link between FTO, dietary protein intake and adiposity
A Westerbork survey of rich clusters of galaxies. II - The luminosity function of bright cluster galaxies at 1415 MHz
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
A Westerbork survey of clusters of galaxies. I - 21 CM observations of A1656, A2147, A2151, A2197 and A2199 - Radio data and identifications
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe