385 research outputs found
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Extragalactic Point Source Search in Five-year WMAP 41, 61 and 94 GHz Maps
We present the results of an extragalactic point source search using the
five-year WMAP 41, 61 and 94 GHz (Q-, V- and W-band) temperature maps. This
work is an extension of our point source search in the WMAP maps applying a
CMB-free technique. An internal linear combination (ILC) map has been formed
from the three-band maps, with the weights chosen to remove the CMB anisotropy
signal as well as to favor a selection of flat-spectrum sources. We find 381
sources at the > 5 sigma level outside the WMAP point source detection mask in
the ILC map, among which 89 are "new" (i.e., not present in the WMAP catalog).
Source fluxes have been calculated and corrected for the Eddington bias. We
have solidly identified 367 (96.3%) of our sources. The 1 sigma positional
uncertainty is estimated to be 2'. The 14 unidentified sources could be either
extended radio structure or obscured by Galactic emission. We have also applied
the same detection process on simulated maps and found 364+/-21 detections on
average. The recovered source distribution N(>S) agrees well with the
simulation input, which proves the reliability of this method.Comment: 28 pages, 9 figures, 2 tables, accepted by Ap
The FRII Broad Line Seyfert 1 Galaxy: PKSJ 1037-2705
In this article, we demonstrate that PKSJ 1037-2705 has a weak accretion flow
luminosity, well below the Seyfert1/QSO dividing line, weak broad emission
lines (BELs) and moderately powerful FRII extended radio emission. It is one of
the few documented examples of a broad-line object in which the time averaged
jet kinetic luminosity, , is larger than the total thermal luminosity
(IR to X-ray) of the accretion flow, . The blazar nucleus dominates
the optical and near ultraviolet emission and is a strong source of hard
X-rays. The strong blazar emission indicates that the relativistic radio jet is
presently active. The implication is that even weakly accreting AGN can create
powerful jets. Kinetically dominated () broad-line objects
provide important constraints on the relationship between the accretion flow
and the jet production mechanism.Comment: To appear in ApJ November 1, 2008, v687n1 issu
Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope
A survey of the North Celestial Pole region using the RATAN-600 radio
telescope at five frequencies in the range 2.3 to 21.7 GHz is described.
Sources were chosen from the NVSS catalogue. The flux densities of 171 sources
in the Declination range +75 to +88 are presented; typical flux density errors
are 5-10 percent including calibration errors. About 20 percent of the sources
have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics
(without last figure with the spectra of the observed sources
A synchrotron self-Compton model with low energy electron cut-off for the blazar S5 0716+714
Rapid inverse Compton cooling sets in when the brightness temperature (T_B)
of a self-absorbed synchrotron source with power-law electrons reaches ~10^{12}
K. However, T_B inferred from observations of intra-day variable sources (IDV)
are well above the "Compton catastrophe" limit. This can be understood if the
underlying electron distribution cuts off at low energy. We approximate a
low-energy cut-off with monoenergetic electrons. We compute the synchrotron
self-Compton (SSC) spectrum of such distribution, and using the IDV source
S5~0716+714 as an example, we compare it to the observed SED of S5~0716+714.
The hard radio spectrum is well-fitted by this model, and the optical data can
be accommodated by a power-law extension to the electron spectrum. We therefore
examine the scenario of an injection of electrons that is a double power law in
energy with a hard low-energy component that does not contribute to the
synchrotron opacity. We show that the double power-law injection model is in
good agreement with the observed SED of S5~0716+714. For intrinsic variability,
we find that a Doppler factor of D\geq30 can explain the observed SED provided
that low-frequency (<32 GHz) emission originates from a larger region than the
higher-frequency emission. To fit the entire spectrum, D\geq65 is needed. We
find the constraint imposed by induced Compton scattering at high T_B is
insignificant in our model. We confirm that electron distribution with a
low-energy cut-off can explain the high T_B in compact radio sources. We show
that synchrotron spectrum from such distributions naturally accounts for the
observed hard radio continuum with a softer optical component, without the need
for an inhomogeneous source.Comment: 13 pages, 5 figures, 1 table, to appear in A&A; refereces removed
from caption of Fig.3, added acknowledgemen
Multi-frequency polarization properties of ten quasars on deca-parsec scales at z > 3
Global VLBI (EVN+VLBA) polarization observations at 5 and 8.4 GHz of ten high
redshift (z > 3) quasars are presented. The core and jet brightness
temperatures are found through modelling the self-calibrated uv-data with
Gaussian components, which provide reliable estimates of the flux density and
size of individual components. The observed high core brightness temperatures
(median K) are consistent with Doppler
boosted emission from a relativistic jet orientated close to the line-of-sight.
This can also explain the dramatic jet bends observed for some of our sources
since small intrinsic bends can be significantly amplified due to projection
effects in a highly beamed relativistic jet. We also model-fit the polarized
emission and, by taking the minimum angle separation between the model-fitted
polarization angles at 5 and 8.4 GHz, we calculate the minimum inferred Faraday
rotation measure (RM) for each component. We also calculate the
minimum intrinsic RM in the rest frame of the AGN (RM =
RM), first subtracting the integrated (presumed foreground)
RM in those cases where we felt we could do this reliably. The resulting mean
core RM is 5580 rad m, with a standard
deviation of 3390 rad m, for four high-z quasars for which we believe we
could reliably remove the foreground RM. We find relatively steep core and jet
spectral index values, with a median core spectral index of -0.3 and a median
jet spectral index of -1.0. Comparing our results with RM observations of more
nearby Active Galactic Nuclei at similar emitted frequencies does not provide
any significant evidence for dependence of the quasar nuclear environment with
redshift.Comment: Published in MNRAS. 18 pages, 7 figures, 5 table
ATPMN: accurate positions and flux densities at 5 and 8 GHz for 8,385 sources from the PMN survey
We present a source catalogue of 9,040 radio sources resulting from
high-resolution observations of 8,385 PMN sources with the Australia Telescope
Compact Array. The catalogue lists flux density and structural measurements at
4.8 and 8.6 GHz, derived from observations of all PMN sources in the
declination range -87 deg < delta < -38.5 deg (exclusive of galactic latitudes
|b| 70 mJy (50 mJy south of delta = -73
deg). We assess the quality of the data, which was gathered in 1992-1994,
describe the population of catalogued sources, and compare it to samples from
complementary catalogues. In particular we find 127 radio sources with probable
association with gamma-ray sources observed by the orbiting Fermi Large Area
Telescope.Comment: 20 pages, 21 figure
Polarization of the WMAP Point Sources
The detection of polarized sources in the WMAP 5-year data is a very
difficult task. The maps are dominated by instrumental noise and only a handful
of sources show up as clear peaks in the Q and U maps. Optimal linear filters
applied at the position of known bright sources detect with a high level of
significance a polarized flux P from many more sources, but estimates of P are
liable to biases. Using a new technique, named the "filtered fusion technique",
we have detected in polarization, with a significance level greater than 99.99%
in at least one WMAP channel, 22 objects, 5 of which, however, do not have a
plausible low radio frequency counterpart and are therefore doubtful. Estimated
polarized fluxes P < 400 mJy at 23 GHz were found to be severely affected by
the Eddington bias. The corresponding polarized flux limit for Planck/LFI at 30
GHz, obtained via realistic simulations, is 300 mJy. We have also obtained
statistical estimates of, or upper limits to the mean polarization degrees of
bright WMAP sources at 23, 33, 41, and 61 GHz, finding that they are of a few
percent.Comment: 10 pages, 6 figures. Accepted for publication in Ap
Giant radio galaxy 0503-286
Discovery of a giant radio galaxy 0503-286 is reported, based on an ongoing search for such objects using the Ooty-Synthesis Radio Telescope at 327 MHz. Maps are also presented of the source made at 1.4 and 2.7 GHz using the 100-meter Effelsberg Radio Telescope. The source is identified with a 15-mag elliptical at a redshift z = 0.038 and has a classical double radio structure extending over 40 arcmin which corresponds to a linear size of 2.5 Mpc (q0 = 0, H0 = 50 km/s-1 Mpc-1). The pronounced asymmetry of its double structure is probably related to the asymmetric environmental conditions that seem to prevail around the parent galaxy. Some properties related to the radio structure of other known giant radio galaxies are also summarized and discussed
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