12,028 research outputs found
Identification of the infrared non-thermal emission in Blazars
Blazars constitute the most interesting and enigmatic class of extragalactic
gamma-ray sources dominated by non-thermal emission. In this Letter, we show
how the WISE infrared data make possible to identify a distinct region of the
[3.4]-[4.6]-[12] micron color-color diagram where the sources dominated by the
the thermal radiation are separated from those dominated by non-thermal
emission, in particular the blazar population. This infrared non-thermal region
delineated as the WISE Blazar Strip (WBS), it is a powerful new diagnostic tool
when the full WISE survey data is released. The WBS can be used to extract new
blazar candidates, to identify those of uncertain type and also to search for
the counterparts of unidentified gamma-ray sources. We show one example of the
value of the use of the WBS identifying the TeV source VER J 0648+152, recently
discovered by VERITAS.Comment: 5 pages, 4 figures, Astrophysical Journal publishe
Child of Steel
[Excerpt] After several months of thinking about what is happening to the working class, particularly the steel industry and the whole system of labor, this poem came to me.
I drive by Homestead Mill every morning to get to my job and to get home I drive past the J&L Steel Mill. Occasionally, I drive through Braddock to the house and street where most of my life was spent.
These are some of the contributing factors which also helped to crystallize this poem
Caveat Emptor: The Meaning of Perception and Integration in Speech Perception
A recent letter^1^ claimed integration of auditory and tactile information in speech perception. Although I have been an advocate of multisensory integration, neither perception nor integration was sufficiently formalized, operationalized, and tested to support this claim
The WISE gamma-ray strip parametrization: the nature of the gamma-ray Active Galactic Nuclei of Uncertain type
Despite the large number of discoveries made recently by Fermi, the origins
of the so called unidentified gamma-ray sources remain unknown. The large
number of these sources suggests that among them there could be a population
that significantly contributes to the isotropic gamma-ray background and is
therefore crucial to understand their nature. The first step toward a complete
comprehension of the unidentified gamma-ray source population is to identify
those that can be associated with blazars, the most numerous class of
extragalactic sources in the gamma-ray sky. Recently, we discovered that
blazars can be recognized and separated from other extragalactic sources using
the infrared (IR) WISE satellite colors. The blazar population delineates a
remarkable and distinctive region of the IR color-color space, the WISE blazar
strip. In particular, the subregion delineated by the gamma-ray emitting
blazars is even narrower and we named it as the WISE Gamma-ray Strip (WGS). In
this paper we parametrize the WGS on the basis of a single parameter s that we
then use to determine if gamma-ray Active Galactic Nuclei of the uncertain type
(AGUs) detected by Fermi are consistent with the WGS and so can be considered
blazar candidates. We find that 54 AGUs out of a set 60 analyzed have IR colors
consistent with the WGS; only 6 AGUs are outliers. This result implies that a
very high percentage (i.e., in this sample about 90%) of the AGUs detected by
Fermi are indeed blazar candidates.Comment: 22 pages, 13 figures, Astrophysical Journal in pres
Infrared Colors of the gamma-ray detected blazars
Blazars constitute the most enigmatic class of extragalactic gamma-ray
sources, and their observational features have been ascribed to a relativistic
jet closely aligned to the line of sight. They are generally divided in two
main classes: the BL Lac objects (BL Lacs) and the Flat Spectrum Radio Quasars
(FSRQs). In the case of BL Lacs the double bumped spectral energy distribution
(SED) is generally described by the Synchrotron Self Compton (SSC) emission,
while for the FSRQs it is interpreted as due to External Compton (EC) emission.
Recently, we showed that in the [3.4]-[4.6]-[12] micron color- color diagram
the blazar population covers a distinct region (i.e., the WISE blazar Strip,
WBS), clearly separated from the other extragalactic sources that are dominated
by thermal emission. In this paper we investigate the relation between the
infrared and gamma-ray emission for a subset of confirmed blazars from the
literature, associated with Fermi sources, for which WISE archival observations
are available. This sample is a proper subset of the sample of sources used
previously, and the availability of Fermi data is critical to constrain the
models on the emission mechanisms for the blazars. We found that the selected
blazars also lie on the WISE blazar Strip covering a narrower region of the
infrared color-color planes than the overall blazars population. We then found
an evident correlation between the IR and gamma-ray spectral indices expected
in the SSC and EC frameworks. Finally, we determined the ratio between their
gamma-ray and infrared fluxes, a surrogate of the ratio of powers between the
inverse Compton and the synchrotron SED components, and used such parameter to
test different emitting scenarios blazars.Comment: 15 pages, 14 figure, accepted for publication in ApJ, to appear in
2012 March 20 editio
Epidemic spreading and risk perception in multiplex networks: a self-organized percolation method
In this paper we study the interplay between epidemic spreading and risk
perception on multiplex networks. The basic idea is that the effective
infection probability is affected by the perception of the risk of being
infected, which we assume to be related to the fraction of infected neighbours,
as introduced by Bagnoli et al., PRE 76:061904 (2007). We re-derive previous
results using a self-organized method, that automatically gives the percolation
threshold in just one simulation. We then extend the model to multiplex
networks considering that people get infected by contacts in real life but
often gather information from an information networks, that may be quite
different from the real ones. The similarity between the real and information
networks determine the possibility of stopping the infection for a sufficiently
high precaution level: if the networks are too different there is no mean of
avoiding the epidemics.Comment: 9 pages, 8 figure
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