739 research outputs found
The Fermi blazars' divide based on the diagnostic of the SEDs peak frequencies
We have studied the quasi-simultaneous Spectral Energy Distributions (SED) of
48 LBAS blazars, detected within the three months of the LAT Bright AGN Sample
(LBAS) data taking period, combining Fermi and Swift data with radio
NIR-Optical and hard-X/gamma-ray data. Using these quasi-simultaneous SEDs,
sampling both the low and the high energy peak of the blazars broad band
emission, we were able to apply a diagnostic tool based on the estimate of the
peak frequencies of the synchrotron (S) and Inverse Compton (IC) components.
Our analysis shows a Fermi blazars' divide based on the peak frequencies of the
SED. The robust result is that the Synchrotron Self Compton (SSC) region
divides in two the plane were we plot the peak frequency of the synchrotron SED
vs the typical Lorentz factor of the electrons most contributing to the
synchrotron emission and to the inverse Compton process. Objects within or
below this region, radiating likely via the SSC process, are
high-frequency-peaked BL Lac object (HBL), or low/intermediate-frequency peaked
BL Lac object (LBL/IBL). All of the IBLs/LBLs within or below the SSC region
are not Compton dominated. The objects lying above the SSC region, radiating
likely via the External radiation Compton (ERC) process, are Flat Spectrum
Radio Quasars and IBLs/LBLs. All of the IBLs/LBLs in the ERC region show a
significant Compton dominance.Comment: Contribution to the Workshop SciNeGHe 2009/Gamma-ray Physics in the
LHC era (Assisi - Italy, Oct. 7-9 2009
Systematic search for gamma-ray periodicity in active galactic nuclei detected by the Fermi Large Area Telescope
We use nine years of gamma-ray data provided by the Fermi Large Area
Telescope (LAT) to systematically study the light curves of more than two
thousand active galactic nuclei (AGN) included in recent Fermi-LAT catalogs.
Ten different techniques are used, which are organized in an automatic
periodicity-search pipeline, in order to search for evidence of periodic
emission in gamma rays. Understanding the processes behind this puzzling
phenomenon will provide a better view about the astrophysical nature of these
extragalactic sources. However, the observation of temporal patterns in
gamma-ray light curves of AGN is still challenging. Despite the fact that there
have been efforts on characterizing the temporal emission of some individual
sources, a systematic search for periodicities by means of a full likelihood
analysis applied to large samples of sources was missing. Our analysis finds 11
AGN, of which 9 are identified for the first time, showing periodicity at more
than 4sigma in at least four algorithms. These findings will help in solving
questions related to the astrophysical origin of this periodic behavior.Comment: 16 pages, 5 figures, 4 tables. Accepted by Ap
Non-Newtonian and flow pulsatility effects in simulation models of a stented intracranial aneurysm
Permission to redistribute provided by publishers.Three models of different stent designs implanted in a cerebral aneurysm, originating from the Virtual Intracranial Stenting Challenge'07, are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software in order to investigate the effects of non-Newtonian viscosity and pulsatile flow. Conventional mass inflow and wall shear stress (WSS) output are used as a means of comparing the cfd simulations. In addition, a WSS distribution is presented, which clearly discriminates in favour of the stent design identified by other groups. It is concluded that non-Newtonian and pulsatile effects are important to include in order to avoid underestimating wss, to understand dynamic flow effects, and to discriminate more effectively between stent designs. © Authors 2011
Towards a new osteometric method for sexing ancient cremated human remains. Analysis of Late Bronze Age and Iron Age samples from Italy with gendered grave goods
Sex estimation of human remains is one of the most important research steps for physical anthropologists and archaeologists dealing with funerary contexts and trying to reconstruct the demographic structure of ancient societies. However, it is well known that in the case of cremations sex assessment might be complicated by the destructive/transformative effect of the fire on bones. Osteometric standards built on unburned human remains and contemporary cremated series are often inadequate for the analysis of ancient cremations, and frequently result in a significant number of misclassifications. This work is an attempt to overcome the scarcity of methods that could be applied to pre-proto-historic Italy and serve as methodological comparison for other European contexts. A set of 24 anatomical traits were measured on 124 Bronze Age and Iron Age cremated individuals with clearly engendered grave goods. Assuming gender largely correlated to sex, male and female distributions of each individual trait measured were compared to evaluate sexual dimorphism through inferential statistics and Chaktaborty and Majumder\u2019s index. The discriminatory power of each variable was evaluated by cross-validation tests. Eight variables yielded an accuracy equal to or greater than 80%. Four of these variables also show a similar degree of precision for both sexes. The most diagnostic measurements are from radius, patella, mandible, talus, femur, first metatarsal, lunate and humerus. Overall, the degree of sexual dimorphism and the reliability of estimates obtained from our series are similar to those of a modern cremated sample recorded by Gon\ue7alves and collaborators. Nevertheless, mean values of the male and female distributions in our case study are lower, and the application of the cut-off point calculated from the modern sample to our ancient individuals produces a considerable number of misclassifications. This result confirms the need to build population-specific methods for sexing the cremated remains of ancient individuals
Gamma-ray Spectral Evolution of NGC1275 Observed with Fermi-LAT
We report on a detailed investigation of the high-energy gamma-ray emission
from NGC\,1275, a well-known radio galaxy hosted by a giant elliptical located
at the center of the nearby Perseus cluster. With the increased photon
statistics, the center of the gamma-ray emitting region is now measured to be
separated by only 0.46' from the nucleus of NGC1275, well within the 95%
confidence error circle with radius ~1.5'. Early Fermi-LAT observations
revealed a significant decade-timescale brightening of NGC1275 at GeV photon
energies, with a flux about seven times higher than the one implied by the
upper limit from previous EGRET observations. With the accumulation of one-year
of Fermi-LAT all-sky-survey exposure, we now detect flux and spectral
variations of this source on month timescales, as reported in this paper. The
average >100 MeV gamma-ray spectrum of NGC1275 shows a possible deviation from
a simple power-law shape, indicating a spectral cut-off around an observed
photon energy of E = 42.2+-19.6 GeV, with an average flux of F = (2.31+-0.13) X
10^{-7} ph/cm^2/s and a power-law photon index, Gamma = 2.13+-0.02. The largest
gamma-ray flaring event was observed in April--May 2009 and was accompanied by
significant spectral variability above E > 1-2 GeV. The gamma-ray activity of
NGC1275 during this flare can be described by a hysteresis behavior in the flux
versus photon index plane. The highest energy photon associated with the
gamma-ray source was detected at the very end of the observation, with the
observed energy of E = 67.4GeV and an angular separation of about 2.4' from the
nucleus. In this paper we present the details of the Fermi-LAT data analysis,
and briefly discuss the implications of the observed gamma-ray spectral
evolution of NGC1275 in the context of gamma-ray blazar sources in general.Comment: 20 pages, 6 figures, accepted for publication in the Ap
A strontium isoscape of Italy for provenance studies
We present a novel database of biological and geological 87Sr/86Sr values (n = 1920) from Italy, using literature data and newly analysed samples, for provenance purposes. We collected both bioavailable and non-bioavailable (i.e. rocks and bulk soils) data to attain a broader view of the Sr isotope variability of the Italian territory. These data were used to build isotope variability maps, namely isoscapes, through Kriging interpolations. We employed two different Kriging models, namely Ordinary Kriging and Universal Kriging, with a geolithological map of Italy categorized in isotope classes as external predictor. Model performances were evaluated through a 10-fold cross validation, yielding accurate 87Sr/86Sr predictions with root mean squared errors (RMSE) ranging between 0.0020 and 0.0024, dependent on the Kriging model and the sample class. Overall, the produced maps highlight a heterogeneous distribution of the 87Sr/86Sr across Italy, with the highest radiogenic values (>0.71) mainly localized in three areas, namely the Alps (Northern Italy), the Tuscany/Latium (Central Italy) and Calabria/Sicily (Southern Italy) magmatic/metamorphic terrains. The rest of the peninsula is characterized by values ranging between 0.707 and 0.710, mostly linked to sedimentary geological units of mixed nature. Finally, we took advantage of the case study of Fratta Polesine, to underscore the importance of choosing appropriate samples when building the local isoscape and of exploring different end-members when interpreting the local Sr isotope variability in mobility and provenance studies. Our user-friendly maps and database are freely accessible through the Geonode platform and will be updated over time to offer a state-of-the-art reference in mobility and provenance studies across the Italian landscape
Flows of people in villages and large centres in Bronze Age Italy through strontium and oxygen isotopes
This study investigates to what extent Bronze Age societies in Northern Italy were permeable accepting and integrating non-local individuals, as well as importing a wide range of raw materials, commodities, and ideas from networks spanning continental Europe and the Mediterranean. During the second millennium BC, the communities of Northern Italy engaged in a progressive stabilization of settlements, culminating in the large polities of the end of the Middle/beginning of the Late Bronze Age pivoted around large defended centres (the Terramare). Although a wide range of exotic archaeological materials indicates that the inhabitants of the Po plain increasingly took part in the networks of Continental European and the Eastern Mediterranean, we should not overlook the fact that the dynamics of interaction were also extremely active on local and regional levels. Mobility patterns have been explored for three key-sites, spanning the Early to Late Bronze Age (1900–1100 BC), namely Sant’Eurosia, Casinalbo and Fondo Paviani, through strontium and oxygen isotope analysis on a large sample size (more than 100 individuals). The results, integrated with osteological and archaeological data, document for the first time in this area that movements of people occurred mostly within a territorial radius of 50 km, but also that larger nodes in the settlement system (such as Fondo Paviani) included individuals from more distant areas. This suggests that, from a demographic perspective, the process towards a more complex socio-political system in Bronze Age Northern Italy was triggered by a largely, but not completely, internal process, stemming from the dynamics of intra-polity networks and local/regional power relationships
The LOFT Ground Segment
LOFT, the Large Observatory For X-ray Timing, was one of the ESA M3 mission
candidates that completed their assessment phase at the end of 2013. LOFT is
equipped with two instruments, the Large Area Detector (LAD) and the Wide Field
Monitor (WFM). The LAD performs pointed observations of several targets per
orbit (~90 minutes), providing roughly ~80 GB of proprietary data per day (the
proprietary period will be 12 months). The WFM continuously monitors about 1/3
of the sky at a time and provides data for about ~100 sources a day, resulting
in a total of ~20 GB of additional telemetry. The LOFT Burst alert System
additionally identifies on-board bright impulsive events (e.g., Gamma-ray
Bursts, GRBs) and broadcasts the corresponding position and trigger time to the
ground using a dedicated system of ~15 VHF receivers. All WFM data are planned
to be made public immediately. In this contribution we summarize the planned
organization of the LOFT ground segment (GS), as established in the mission
Yellow Book 1 . We describe the expected GS contributions from ESA and the LOFT
consortium. A review is provided of the planned LOFT data products and the
details of the data flow, archiving and distribution. Despite LOFT was not
selected for launch within the M3 call, its long assessment phase (> 2 years)
led to a very solid mission design and an efficient planning of its ground
operations.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
High Momentum Probes of Nuclear Matter
We discuss how the chemical composition of QCD jets is altered by final state
interactions in surrounding nuclear matter. We describe this process through
conversions of leading jet particles. We find that conversions lead to an
enhancement of kaons at high transverse momentum in Au+Au collisions at RHIC,
while their azimuthal asymmetry v_2 is suppressed.Comment: Contribution to the 4th international workshop High-pT physics at LHC
09, Prague; 6 pages, 6 figure
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