467 research outputs found
Simulations of the X-ray imaging capabilities of the Silicon Drift Detectors (SDD) for the LOFT Wide Field Monitor
The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the
four Cosmic Vision M3 candidate missions to undergo an assessment phase, will
revolutionize the study of compact objects in our galaxy and of the brightest
supermassive black holes in active galactic nuclei. The Large Area Detector
(LAD), carrying an unprecedented effective area of 10 m^2, is complemented by a
coded-mask Wide Field Monitor, in charge of monitoring a large fraction of the
sky potentially accessible to the LAD, to provide the history and context for
the sources observed by LAD and to trigger its observations on their most
interesting and extreme states. In this paper we present detailed simulations
of the imaging capabilities of the Silicon Drift Detectors developed for the
LOFT Wide Field Monitor detection plane. The simulations explore a large
parameter space for both the detector design and the environmental conditions,
allowing us to optimize the detector characteristics and demonstrating the
X-ray imaging performance of the large-area SDDs in the 2-50 keV energy band.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-210, 201
Gamma-ray blazars: the view from AGILE
During the first 3 years of operation the Gamma-Ray Imaging Detector onboard
the AGILE satellite detected several blazars in a high gamma-ray activity: 3C
279, 3C 454.3, PKS 1510-089, S5 0716+714, 3C 273, W Comae, Mrk 421, PKS
0537-441 and 4C +21.35. Thanks to the rapid dissemination of our alerts, we
were able to obtain multiwavelength data from other observatories such as
Spitzer, Swift, RXTE, Suzaku, INTEGRAL, MAGIC, VERITAS, and ARGO as well as
radio-to-optical coverage by means of the GASP Project of the WEBT and the REM
Telescope. This large multifrequency coverage gave us the opportunity to study
the variability correlations between the emission at different frequencies and
to obtain simultaneous spectral energy distributions of these sources from
radio to gamma-ray energy bands, investigating the different mechanisms
responsible for their emission and uncovering in some cases a more complex
behaviour with respect to the standard models. We present a review of the most
interesting AGILE results on these gamma-ray blazars and their multifrequency
data.Comment: 25 pages, 10 figures, accepted for publication on Advances in Space
Research. Talk presented at the 38th COSPAR Scientific Assembly (Bremen,
Germany; July 18-25, 2010
Multiproxy bioarchaeological data reveals interplay between growth, diet and population dynamics across the transition to farming in the central Mediterranean
The transition to farming brought on a series of important changes in human society, lifestyle, diet and health. The human bioarchaeology of the agricultural transition has received much attention, however, relatively few studies have directly tested the interrelationship between individual lifestyle factors and their implications for understanding life history changes among the first farmers. We investigate the interplay between skeletal growth, diet, physical activity and population size across 30,000 years in the central Mediterranean through a ‘big data’ cross-analysis of osteological data related to stature (n = 361), body mass (n = 334) and long bone biomechanics (n = 481), carbon (δ 13C) and nitrogen (δ 15N) stable isotopes (n = 1986 human, n = 475 animal) and radiocarbon dates (n = 5263). We present the observed trends on a continuous timescale in order to avoid grouping our data into assigned ‘time periods’, thus achieving greater resolution and chronological control over our analysis. The results identify important changes in human life history strategies associated with the first farmers, but also highlight the long-term nature of these trends in the millennia either side of the agricultural transition. The integration of these different data is an important step towards disentangling the complex relationship between demography, diet and health, and reconstruct life history changes within a southern European context. We believe the methodological approach adopted here has broader global implications for bioarchaeological studies of human adaptation more generally
The extraordinary gamma-ray flare of the blazar 3C 454.3
We present the gamma-ray data of the extraordinary flaring activity above 100
MeV from the flat spectrum radio quasar 3C 454.3 detected by AGILE during the
month of December 2009. 3C 454.3, that has been among the most active blazars
of the FSRQ type since 2007, was detected in the gamma-ray range with a
progressively rising flux since November 10, 2009. The gamma-ray flux reached a
value comparable with that of the Vela pulsar on December 2, 2009. Remarkably,
between December 2 and 3, 2009 the source more than doubled its gamma-ray
emission and became the brightest gamma-ray source in the sky with a peak flux
of F_{\gamma,p} = (2000 \pm 400) x 10^-8 ph cm^-2 s^-1 for a 1-day integration
above 100 MeV. The gamma-ray intensity decreased in the following days with the
source flux remaining at large values near F \simeq (1000 \pm 200) x 10^-8 ph
cm^-2 s^-1 for more than a week. This exceptional gamma-ray flare dissipated
among the largest ever detected intrinsic radiated power in gamma-rays above
100 MeV (L_{\gamma, source, peak} \simeq 3 x 10^46 erg s^-1, for a relativistic
Doppler factor of {\delta} \simeq 30). The total isotropic irradiated energy of
the month-long episode in the range 100 MeV - 3 GeV is E_{\gamma,iso} \simeq
10^56 erg. We report the intensity and spectral evolution of the gamma-ray
emission across the flaring episode. We briefly discuss the important
theoretical implications of our detection.Comment: 17 pages, 3 figures, ApJ accepte
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