1,464 research outputs found
The nature of optical and near-infrared variability of BL Lacertae
Since 1997, BL Lacertae has undergone a phase of high optical activity, with
the occurrence of several prominent outbursts. Starting from 1999, the Whole
Earth Blazar Telescope (WEBT) consortium has organized various multifrequency
campaigns on this blazar, collecting tens of thousands of data points. One of
the main issues in the analysis of this huge dataset has been the study of
colour variability. The massive amount of optical and near-infrared data
collected during the campaigns enables us to perform a deep analysis of
multiband data, with the aim of understanding the flux variability mechanisms.
We use a new approach for the analysis of these data, focusing on the source
spectral evolution. We show that the overall behaviour of the BL Lacertae light
and colour curves can be explained in terms of changing viewing angle of a
moving, discrete emitting region, which causes variable Doppler boosting of the
corresponding radiation. A fractal helical structure is suggested to be at the
origin of the different time scales of variability.Comment: 6 pages, 8 figures, accepted by A&
The long-term optical spectral variability of BL Lacertae
We present the results from a study of the long-term optical spectral
variations of BL Lacertae, using the long and well-sampled B and R-band light
curves of the Whole Earth Blazar Telescope (WEBT) collaboration, binned on time
intervals of 1 day. The relation between spectral slope and flux (the spectrum
gets bluer as the source flux increases) is well described by a power-law
model, although there is significant scatter around the best-fitting model
line. To some extent, this is due to the spectral evolution of the source
(along well-defined loop-like structures) during low-amplitude events, which
are superimposed on the major optical flares, and evolve on time scales of a
few days. The "bluer-when-brighter" mild chromatism of the long-term variations
of the source can be explained if the flux increases/decreases faster in the B
than in the R band. The B and R-band variations are well correlated, with no
significant, measurable delays larger than a few days. On the other hand, we
find that the spectral variations lead those in the flux light curves by ~ 4
days. Our results can be explained in terms of Doppler factor variations due to
changes in the viewing angle of a curved and inhomogeneous emitting jet.Comment: 7 pages, 5 figures, accepted for publication in A&
Gravitational interaction of antimatter
Until now, there is no experimental evidence on the gravitational behaviour
of antimatter. While we may be confident that antimatter attracts antimatter,
we do not know anything on the interaction between matter and antimatter. We
investigate this issue on theoretical grounds. Starting from the CPT invariance
of physical laws, we transform matter into antimatter in the equations of both
electrodynamics and gravitation. In the former case, the result is the
well-known change of sign of the electric charge. In the latter, we find that
the gravitational interaction between matter and antimatter is a mutual
repulsion. This result supports cosmological models attempting to explain the
Universe accelerated expansion in terms of a matter-antimatter symmetry.Comment: 5 pages, submitted to General Relativity and Gravitation on 2
February 201
Towards a Benchmark of Natural Language Arguments
The connections among natural language processing and argumentation theory
are becoming stronger in the latest years, with a growing amount of works going
in this direction, in different scenarios and applying heterogeneous
techniques. In this paper, we present two datasets we built to cope with the
combination of the Textual Entailment framework and bipolar abstract
argumentation. In our approach, such datasets are used to automatically
identify through a Textual Entailment system the relations among the arguments
(i.e., attack, support), and then the resulting bipolar argumentation graphs
are analyzed to compute the accepted arguments
The Correlated Multi-color Optical Variations of BL Lac Object S5 0716+714
S5 0716+714 is a well-studied BL Lac object in the sky. Verifying the
existence of correlations among the flux variations in different bands serves
as an important tool to investigate the emission processes. To examine the
possible existence of a lag between variations in different optical bands on
this source, we employ a discrete correlation function (DCF) analysis on the
light curves. In order to obtain statistically meaningful values for the
cross-correlation time lags and their related uncertainties, we perform Monte
Carlo simulations called "flux redistribution/random subset selection"
(FR/RSS). Our analysis confirms that the variations in different optical light
curves are strongly correlated. The time lags show a hint of the variations in
high frequency band leading those in low frequency band of the order of a few
minutes.Comment: 6 pages, 5 figures, 3 tables. This paper has been accepted for
publication in PASA
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