10,174 research outputs found
The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
We present the results of polarimetric ( band) and multicolor photometric
() observations of the blazar AO 0235+16 during an outburst in 2006
December. The data reveal a short timescale of variability (several hours),
which increases from optical to near-IR wavelengths; even shorter variations
are detected in polarization. The flux density correlates with the degree of
polarization, and at maximum degree of polarization the electric vector tends
to align with the parsec-scale jet direction. We find that a variable component
with a steady power-law spectral energy distribution and very high optical
polarization (30-50%) is responsible for the variability. We interpret these
properties of the blazar withina model of a transverse shock propagating down
the jet. In this case a small change in the viewing angle of the jet, by
, and a decrease in the shocked plasma compression by a factor of
1.5 are sufficient to account for the variability.Comment: 22 pages, 8 figures, accepted for Ap
Soluble field theory with a massless gauge invariant limit
It is shown that there exists a soluble four parameter model in (1+1)
dimensions all of whose propagators can be determined in terms of the
corresponding known propagators of the vector coupling theory. Unlike the
latter case, however, the limit of zero bare mass is nonsingular and yields a
nontrivial theory with a rigorously unbroken gauge invariance.Comment: 7 pages, revtex, no figure
Unification of the Soluble Two-dimensional vector coupling models
The general theory of a massless fermion coupled to a massive vector meson in
two dimensions is formulated and solved to obtain the complete set of Green's
functions. Both vector and axial vector couplings are included. In addition to
the boson mass and the two coupling constants, a coefficient which denotes a
particular current definition is required for a unique specification of the
model.
The resulting four parameter theory and its solution are shown to reduce in
appropriate limits to all the known soluble models, including in particular the
Schwinger model and its axial vector variant.Comment: 10 page
Color Variability of the Blazar AO 0235+16
Multicolor (UBVRIJHK) observations of the blazar AO 0235+16 are analyzed. The
light curves were compiled at the Turin Observatory from literature data and
the results of observations obtained in the framework of the WEBT program
(http://www.to.astro/blazars/webt/). The color variability of the blazar was
studied in eight time intervals with a sufficient number of multicolor optical
observations; JHK data are available for only one of these. The spectral energy
distribution (SED) of the variable component remained constant within each
interval, but varied strongly from one interval to another. After correction
for dust absorption, the SED can be represented by a power law in all cases,
providing evidence for a synchrotron nature of the variable component. We show
that the variability at both optical and IR wavelengths is associated with the
same variable source.Comment: 11 pages, 9 figures, 4 tables, accepted for publication in Astronomy
Report
Energy spectra of cosmic ray nuclei: 4z26 and .3E2 GeV/amu
Energy spectra of cosmic ray nuclei in the charge range 5 is less than or equal to z less than or equal to 26 have been derived from the response of an acrylic plastic Cerenkov detector. Data were obtained using a balloon borne detector and cover the energy range 320 is approximately less than e approximately less than 2200 MeV. amu. Spectra are derived from a formal deconvolution using the method of Lezniak (1975). Relative spectra of different elements are compared by observing charge ratios. Secondary primary ratios are observed to decrease with increasing energy, consistent with the effect previously observed at higher energy. Primary to primary ratios are constant for 6 is less than or equal to z less than or equal to 26 and 14 is less than or equal to z less than or equal to 26 but vary for 10 is less than or equal to z less than or equal to 14. This data is found to be consistent with existing data where comparable and lends strong support ot the idea of two separate source populations contributing to the cosmic ray composition
Ab-initio coupled-cluster effective interactions for the shell model: Application to neutron-rich oxygen and carbon isotopes
We derive and compute effective valence-space shell-model interactions from
ab-initio coupled-cluster theory and apply them to open-shell and neutron-rich
oxygen and carbon isotopes. Our shell-model interactions are based on
nucleon-nucleon and three-nucleon forces from chiral effective-field theory. We
compute the energies of ground and low-lying states, and find good agreement
with experiment. In particular our calculations are consistent with the N=14,
16 shell closures in oxygen-22 and oxygen-24, while for carbon-20 the
corresponding N=14 closure is weaker. We find good agreement between our
coupled-cluster effective-interaction results with those obtained from standard
single-reference coupled-cluster calculations for up to eight valence neutrons
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