3,079 research outputs found
SSC radiation in BL Lac sources, the end of the tether
The synchrotron-self Compton (SSC) radiation process is widely held to
provide a close representation of the double peaked spectral energy
distributions from BL Lac Objects (BL Lacs), which are marked by non-thermal
beamed radiations, highly variable on timescales of days or less. Their
outbursts in the gamma ray relative to the optical/X rays might be surmised to
be enhanced in BL Lacs as these photons are upscattered via the inverse Compton
(IC) process. From the observed correlations among the spectral parameters
during optical/X-ray variations we aim at predicting corresponding correlations
in the gamma-ray band, and the actual relations between the gamma-ray and the
X-ray variability consistent with the SSC emission process. We start from the
homogeneous single-zone SSC source model, with log-parabolic energies
distributions of emitting electron as required by the X-ray data of many
sources. We find relations among spectral parameters of the IC radiation in
both the Thomson (for Low energy BL Lacs) and the Klein-Nishina regimes (mainly
for High energy BL Lacs) and we compute how variability is driven by a smooth
increase of key source parameters, primarily the root mean square electron
energy. The single component SSC source model in the Thomson regime turns out
to be adequate for many LBL sources. However, the simple model meets its limits
with the fast/strong flares recently reported for a few sources in the TeV
range; these require sudden accelerations of emitting electrons in a second
source component.Comment: 12 pages, 2 tables, 8 figure
New blazars from the cross-match of recent multi-frequency catalogs
Blazars are radio-loud active galactic nuclei well known for their non
thermal emission spanning a wide range of frequencies. The Roma-BZCAT is, to
date, the most comprehensive list of these sources. We performed the
cross-match of several catalogs obtained from recent surveys at different
frequencies to search for new blazars. We cross-matched the 1 Swift-XRT
Point Source catalog with the spectroscopic sample of the 9 Data Release
of the Sloan Digital Sky Survey. Then, we performed further cross-matches with
the catalogs corresponding to the Faint Images of the Radio Sky at Twenty cm
survey and to the AllWISE Data release, focusing on sources with infrared
colors similar to those of confirmed -ray blazars included in the
Second Fermi-LAT catalog. As a result, we obtained a preliminary list of
objects with all the elements needed for a proper blazar classification
according to the prescriptions of the Roma-BZCAT. We carefully investigated
additional properties such as their morphology and the slope of their spectral
energy distribution in the radio domain, the features shown in their optical
spectrum, and the luminosity in the soft X rays to exclude generic active
galactic nuclei and focus on authentic blazar-like sources. At the end of our
screening we obtained a list of 15 objects with firmly established blazar
properties.Comment: 8 pages, 3 figures, 1 table. Accepted for publication in Astrophysics
and Space Science on 2015 April 25. Corrected typo in Section
WATCAT: a tale of wide-angle tailed radio galaxies
We present a catalog of 47 wide-angle tailed radio galaxies (WATs), the
WATCAT; these galaxies were selected by combining observations from the
National Radio Astronomy Observatory/Very Large Array Sky Survey (NVSS), the
Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), and the Sloan
Digital Sky Survey (SDSS), and mainly built including a radio morphological
classification. We included in the catalog only radio sources showing two-sided
jets with two clear "warmspots" (i.e., jet knots as bright as 20% of the
nucleus) lying on the opposite side of the radio core, and having classical
extended emission resembling a plume beyond them. The catalog is limited to
redshifts z 0.15, and lists only sources with radio emission extended
beyond 30 kpc from the host galaxy. We found that host galaxies of WATCAT
sources are all luminous (-20.5 Mr -23.7), red early-type
galaxies with black hole masses in the range M M. The spectroscopic classification indicates that they
are all low-excitation galaxies (LEGs). Comparing WAT multifrequency properties
with those of FRI and FRII radio galaxies at the same redshifts, we conclude
that WATs show multifrequency properties remarkably similar to FRI radio
galaxies, having radio power of typical FRIIs
Swift XRT and UVOT deep observations of the high energy peaked BL Lac object PKS 0548-322 close to its brightest state
We present the results of a spectral analysis of 5 Swift XRT and UVOT
observations of the BL Lac object PKS 0548-322 carried out over the period
April-June 2005. The X-ray flux of this high energy peaked BL Lac (HBL) source
was found to be approximately constant at a level of F(2-10 keV) ~ 4x10^-11 erg
cm^-2 s^-1, a factor of 2 brighter than when observed by BeppoSAX in 1999 and
close to the maximum intensity reported in the Einstein Slew Survey. The very
good statistics obtained in the 0.3-10 keV Swift X-ray spectrum allowed us to
detect highly significant deviations from a simple power law spectral
distribution. A log-parabolic model describes well the X-ray data and gives a
best fit curvature parameter of 0.18 and peak energy in the Spectral Energy
Distribution of about 2 keV. The UV spectral data from Swift UVOT join well
with a power law extrapolation of the soft X-ray data points suggesting that
the same component is responsible for the observed emission in the two bands.
The combination of synchrotron peak in the X-ray band and high intensity state
confirms PKS 0548-322 as a prime target for TeV observations. X-ray monitoring
and coordinated TeV campaigns are highly advisable.Comment: Accepted for publication in A&A (6 pages, 3 figures
Origin of TeV Galactic Cosmic Rays
We consider a possibility of identification of sources of cosmic rays (CR) of
the energy above 1 TeV via observation of degree-scale extended gamma-ray
emission which traces the locations of recent sources in the Galaxy. Such
emission in the energy band above 100 GeV is produced by CR nuclei and
electrons released by the sources and spreading into the interstellar medium.
We use the data from the Fermi gamma-ray telescope to locate the degree-scale
100 GeV gamma-ray sources. We find that the number of such sources and their
overall power match to those expected when CRs injection events happen every
~100 yr in portions of ~1e50 erg. We find that most of the sources are
associated to pulsars with spin down age less than ~30 kyr and hence to the
recent supernova explosions. This supports the hypothesis of supernova origin
of Galactic CRs. We notice that the degree-scale extended emission does not
surround shell-like supernova remnants without pulsars. Based on this
observation, we argue that the presence of the pulsar is essential for the CR
acceleration process. We expect that a significant fraction of the degree-scale
sources should be detectable as extended sources with km3-scale neutrino
detectors.Comment: 14 pages, 14 figures, accepted for publication in Phys.Rev.
Optical archival spectra of blazar candidates of uncertain type in the 3 Fermi Large Area Telescope Catalog
Despite the fact that blazars constitute the rarest class among active
galactic nuclei (AGNs) they are the largest known population of associated
-ray sources. Many of the -ray objects listed in the
Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar
candidates of uncertain type (BCUs), either because they show multifrequency
behaviour similar to blazars but lacking optical spectra in the literature, or
because the quality of such spectra is too low to confirm their nature. Here we
select, out of 585 BCUs in the 3FGL, 42 BCUs which we identify as probable
blazars by their WISE infrared colors and which also have optical spectra that
are available in the Sloan Digital Sky Survey (SDSS) and/or Six-Degree Field
Galaxy Survey Database (6dFGS). We confirm the blazar nature of all of the
sources. We furthermore conclude that 28 of them are BL Lacs, 8 are radio-loud
quasars with flat radio spectrum and 6 are BL Lac whose emission is dominated
by their host galaxy
Refining the associations of the Fermi Large Area Telescope Source Catalogs
The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released
in February 2010 and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in
April 2012, based on data from 24 months of operation. Since their releases,
many follow up observations of unidentified gamma-ray sources (UGSs) were
performed and new procedures to associate gamma-ray sources with potential
counterparts at other wavelengths were developed. Here we review and
characterize all the associations as published in the 1FGL and 2FGL catalog on
the basis of multifrequency archival observations. In particular we located 177
spectra for the low-energy counterparts that were not listed in the previous
Fermi catalogs, and in addition we present new spectroscopic observations of 8
gamma-ray blazar candidates. Based on our investigations, we introduce a new
counterpart category of "candidate associations" and propose a refined
classification for the candidate low-energy counterparts of the Fermi sources.
We compare the 1FGL-assigned counterparts with those listed in the 2FGL to
determine which unassociated sources became associated in later releases of the
Fermi catalogs. We also search for potential counterparts to all the remaining
unassociated Fermi sources. Finally, we prepare a refined and merged list of
all the associations of the 1FGL plus 2FGL catalogs that includes 2219 unique
Fermi objects. This is the most comprehensive and systematic study of all the
associations collected for the gamma-ray sources available to date. We conclude
that 80% of the Fermi sources have at least one known plausible gamma-ray
emitter within their positional uncertainty regions.Comment: 26 pages, 24 figures, 7 tables, ApJS accepted for publication
(pre-proof version uploaded
Periodic patterns for resolution limit characterization of correlation plenoptic imaging
The measurement of the spatio-temporal correlations of light provides an
interesting tool to overcome the traditional limitations of standard imaging,
such as the strong trade-off between spatial resolution and depth of field. In
particular, using correlation plenoptic imaging, one can detect both the
spatial distribution and the direction of light in a scene, pushing both
resolution and depth of field to the fundamental limit imposed by wave-optics.
This allows one to perform refocusing of different axial planes and
three-dimensional reconstruction without any spatial scanning. In the present
work, we investigate the resolution limit in a particular correlation plenoptic
imaging scheme, by considering periodic test patterns, which provide, through
analytical results, a deeper insight in the resolution properties of this
second-order imaging technique, also in comparison with standard imaging.Comment: 16 pages, 4 figure
Genetic, hormonal and metabolic aspects of PCOS: An update
Polycystic ovary syndrome (PCOS) is a complex endocrine disorder affecting 5-10 % of women of reproductive age. It generally manifests with oligo/anovulatory cycles, hirsutism and polycystic ovaries, together with a considerable prevalence of insulin resistance. Although the aetiology of the syndrome is not completely understood yet, PCOS is considered a multifactorial disorder with various genetic, endocrine and environmental abnormalities. Moreover, PCOS patients have a higher risk of metabolic and cardiovascular diseases and their related morbidity, if compared to the general population
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