1,446 research outputs found
Analysis of the Spectral Energy Distributions of Fermi bright blazars
Blazars are a small fraction of all extragalactic sources but, unlike other
objects, they are strong emitters across the entire electromagnetic spectrum.
In this study we have conducted a detailed investigation of the broad-band
spectral properties of the gamma-ray selected blazars of the Fermi-LAT Bright
AGN Sample (LBAS). By combining the accurately estimated Fermi gamma-ray
spectra with Swift, radio, NIR-Optical and hard-X/gamma-ray data, collected
within three months of the LBAS data taking period, we were able to assemble
high-quality and quasi-simultaneous Spectral Energy Distributions (SED) for 48
LBAS blazars.Comment: 6 pages, 8 figures, "2009 Fermi Symposium", "eConf Proceedings
C091122
Study of microwave/gamma-ray properties for Fermi-LAT bright AGNs
Blazars are a small fraction of all extragalactic sources but, unlike other
objects, they are strong emitters across the entire electromagnetic spectrum.
Recent data in the microwave region of the electromagnetic spectrum have become
available to allow for systematic studies of blazars over large cosmological
volumes. This frequency band is indeed particularly suited for the selection of
blazars since at these frequencies the contamination from radio extended
components with steep spectra is no longer present and the emission from the
accretion process is negligible. During the first 3 months of scientific
operations Fermi-LAT detected 106 bright, high-galactic latitude (| b |> 10
deg) AGNs with high significance. In this study we investigate the possible
relations between the microwave and the gamma-ray emissions for Fermi-LAT
detected AGNs belonging to WMAP 5th year bright source catalog.Comment: 3 pages, 3 ps figures, "2009 Fermi Symposium", "eConf Proceedings
C091122
Blazar surveys with WMAP and Swift
We present the preliminary results from two new surveys of blazars that have
direct implications on the GLAST detection of extragalactic sources from two
different perspectives: microwave selection and a combined deep X-ray/radio
selection. The first one is a 41 GHz flux-limited sample extracted from the
WMAP 3-yr catalog of microwave point sources. This is a statistically well
defined sample of about 200 blazars and radio galaxies, most of which are
expected to be detected by GLAST. The second one is a new deep survey of
Blazars selected among the radio sources that are spatially coincident with
serendipitous sources detected in deep X-ray images (0.3-10 keV) centered on
the Gamma Ray Bursts (GRB) discovered by the Swift satellite. This sample is
particularly interesting from a statistical viewpoint since a) it is unbiased
as GRBs explode at random positions in the sky, b) it is very deep in the X-ray
band (\fx \simgt \ergs) with a position accuracy of a few
arc-seconds, c) it will cover a fairly large (20-30 square deg.) area of sky,
d) it includes all blazars with radio flux (1.4 GHz) larger than 10 mJy, making
it approximately two orders of magnitude deeper than the WMAP sample and about
one order of magnitude deeper than the deepest existing complete samples of
radio selected blazars, and e) it can be used to estimate the amount of
unresolved GLAST high latitude gamma-ray background and its anisotropy
spectrum.Comment: 3 pages, 3 figures, to appear in Proc. of the 1st GLAST Symposium,
Feb 5-8, 2007, Stanford, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meega
Dynamic of a lacustrine sedimentary system during late rifting at the Cretaceous‐Palaeocene transition: Example of the Yacoraite Formation, Salta Basin, Argentina
The architecture of lacustrine systems is the result of the complex interaction between tectonics, climate and environmental parameters, and constitute the main forcing parameters on the lake dynamics. Field analogue studies have been performed to better assess such interactions, and their impact on the facies distribution and the stratigraphic architecture of lacustrine systems. The Yacoraite Formation (Late Cretaceous/Early Palaeocene), deposited during the sag phase of the Salta rift basin in Argentina, is exposed in world-class outcrops that allowed the dynamics of this lacustrine system to be studied through facies analysis and stratigraphic evolution. On the scale of the Alemania-Met\ue1n-El Rey Basin, the Yacoraite Formation is organized with a siliciclastic-dominated margin to the west, and a carbonate-dominated margin to the east. The Yacoraite can be subdivided into four main \u2018mid-term\u2019 sequences and further subdivided into \u2018short-term\u2019 sequences recording high frequency climate fluctuations. Furthermore, the depositional profiles and identified system tracts have been grouped into two end-members at basin scale: (a) a balanced \u2018perennial\u2019 depositional system for the lower part of the Yacoraite Formation and (b) a highly alternating \u2018ephemeral\u2019 depositional system for the upper part of the Yacoraite Formation. The transition from a perennial system to an ephemeral system indicates a change in the sedimentary dynamics of the basin, which was probably linked with the Cretaceous/Tertiary boundary that induced a temporary shutdown of carbonate production and an increase in siliciclastic supply
High-redshift blazars through nustar eyes
The most powerful sources among the blazar family are MeV blazars. Often
detected at , they usually display high X- and \gm-ray luminosities,
larger-than-average jet powers and black hole masses .
In the present work we perform a multiwavelength study of three high redshift
blazars: 3FGL J0325.5+2223 (), 3FGL J0449.0+1121 (), and 3FGL
J0453.22808 (), analysing quasi simultaneous data from GROND,
\swift-UVOT and XRT, \nustar, and \fermi-LAT. Our main focus is on the hard
X-ray band recently unveiled by \nustar~(379 keV) where these objects show a
hard spectrum which enables us to constrain the inverse Compton peak and the
jet power. We found that all three targets resemble the most powerful blazars,
with the synchrotron peak located in the sub-millimeter range and the inverse
Compton peak in the MeV range, and therefore belong to the MeV blazar class.
Using a simple one zone leptonic emission model to reproduce the spectral
energy distributions, we conclude that a simple combination of synchrotron and
accretion disk emission reproduces the infrared-optical spectra while the X-ray
to \gm-ray part is well reproduced by the inverse Compton scattering of low
energy photons supplied by the broad line region. The black hole masses for
each of the three sources are calculated to be . The three studied sources have jet power at the level of, or
beyond, the accretion luminosity.Comment: 4 figures, 3 tables, accepted for publication in Ap
Impact of diagenesis on the spatial and temporal distribution of reservoir quality in the Jurassic Arab D and C members, offshore Abu Dhabi oilfield, United Arab Emirates
This study is based on petrographic examination (optical, scanning electron microscope, cathodo-luminescence, backscattered electron imaging, and fluorescence) of 1, 350 thin sections as well as isotopic compositions of carbonates (172 carbon and oxygen and 118 strontium isotopes), microprobe analyses, and fluid inclusion microthermometry of cored Jurassic Arab D and C members from 16 wells in a field from offshore Abu Dhabi, United Arab Emirates. The formation was deposited in a ramp with barrier islands and distal slope setting. Petrographic, stable isotopic and fluid-inclusion analyses have unraveled the impact of diagenesis on reservoir quality of Arab D and C within the framework of depositional facies, sequence stratigraphy, and burial history. Diagenetic processes include cementation by grain rim cement and syntaxial calcite overgrowths, formation of moldic porosity by dissolution of allochems, dolomitization and dolomite cementation, cementation by gypsum and anhydrite, and stylolitization. Partial eogenetic calcite and dolomite cementation has prevented porosity loss in grainstones during burial diagenesis. Dolomitization and sulphate cementation of peritidal mud are suggested to have occurred in an evaporative sabkha setting, whereas dolomitization of subtidal packstones and grainstones was driven by seepage reflux of lagoon brines formed during major falls in relative sea level. Recrystallization of dolomite occurred by hot saline waters (Th 85-100\ub0C; and salinity 14-18 wt% NaCl). Anhydrite and gypsum cements (Th 95-105\ub0C; fluid salinity 16-20 wt% NaCl), were subjected to extensive dissolution, presumably caused by thermal sulfate reduction followed by a major phase of oil emplacement. The last cement recorded was a second phase of anhydrite and gypsum (Th 95-120\ub0C; 16-22 wt% NaCl), which fills fractures associated with faults
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