10,265 research outputs found
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
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
The Evolution of the Far-UV Luminosity Function and Star Formation Rate Density of the Chandra Deep Field South from z=0.2-1.2 with Swift/UVOT
We use deep Swift UV/Optical Telescope (UVOT) near-ultraviolet (1600A to
4000A) imaging of the Chandra Deep Field South to measure the rest-frame far-UV
(FUV; 1500A) luminosity function (LF) in four redshift bins between z=0.2 and
1.2. Our sample includes 730 galaxies with u < 24.1 mag. We use two methods to
construct and fit the LFs: the traditional V_max method with bootstrap errors
and a maximum likelihood estimator. We observe luminosity evolution such that
M* fades by ~2 magnitudes from z~1 to z~0.3 implying that star formation
activity was substantially higher at z~1 than today. We integrate our LFs to
determine the FUV luminosity densities and star formation rate densities from
z=0.2 to 1.2. We find evolution consistent with an increase proportional to
(1+z)^1.9 out to z~1. Our luminosity densities and star formation rates are
consistent with those found in the literature, but are, on average, a factor of
~2 higher than previous FUV measurements. In addition, we combine our UVOT data
with the MUSYC survey to model the galaxies' ultraviolet-to-infrared spectral
energy distributions and estimate the rest-frame FUV attenuation. We find that
accounting for the attenuation increases the star formation rate densities by
~1 dex across all four redshift bins.Comment: 20 pages, 8 figures, 6 tables; accepted for publication in Ap
Global-in-time solutions for the isothermal Matovich-Pearson equations
In this paper we study the Matovich-Pearson equations describing the process
of glass fiber drawing. These equations may be viewed as a 1D-reduction of the
incompressible Navier-Stokes equations including free boundary, valid for the
drawing of a long and thin glass fiber. We concentrate on the isothermal case
without surface tension. Then the Matovich-Pearson equations represent a
nonlinearly coupled system of an elliptic equation for the axial velocity and a
hyperbolic transport equation for the fluid cross-sectional area. We first
prove existence of a local solution, and, after constructing appropriate
barrier functions, we deduce that the fluid radius is always strictly positive
and that the local solution remains in the same regularity class. To the best
of our knowledge, this is the first global existence and uniqueness result for
this important system of equations
New Gauge Invariant Formulation of the Chern-Simons Gauge Theory
A new gauge invariant formulation of the relativistic scalar field
interacting with Chern-Simons gauge fields is considered. This formulation is
consistent with the gauge fixed formulation. Furthermore we find that canonical
(Noether) Poincar\'e generators are not gauge invariant even on the constraints
surface and do not satisfy the (classical) Poincar\'e algebra. It is the
improved generators, constructed from the symmetric energy-momentum tensor,
which are (manifestly) gauge invariant and obey the classical Poincar\'e
algebra.Comment: Shortened, to appear as Papid Communication-PRD/Nov/9
On the Classification of UGC1382 as a Giant Low Surface Brightness Galaxy
We provide evidence that UGC1382, long believed to be a passive elliptical
galaxy, is actually a giant low surface brightness (GLSB) galaxy which rivals
the archetypical GLSB Malin 1 in size. Like other GLSB galaxies, it has two
components: a high surface brightness disk galaxy surrounded by an extended low
surface brightness (LSB) disk. For UGC1382, the central component is a
lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk
has an effective radius of ~38 kpc and an extrapolated central surface
brightness of ~26 mag/arcsec^2. Both components have a combined stellar mass of
~8x10^10 M_sun, and are embedded in a massive (10^10 M_sun) low-density (<3
M_sun/pc^2) HI disk with a radius of 110 kpc, making this one of the largest
isolated disk galaxies known. The system resides in a massive dark matter halo
of at least 2x10^12 M_sun. Although possibly part of a small group, its low
density environment likely plays a role in the formation and retention of the
giant LSB and HI disks. We model the spectral energy distributions and find
that the LSB disk is likely older than the lenticular component. UGC1382 has
UV-optical colors typical of galaxies transitioning through the green valley.
Within the LSB disk are spiral arms forming stars at extremely low
efficiencies. The gas depletion time scale of ~10^11 yr suggests that UGC1382
may be a very long term resident of the green valley. We find that the
formation and evolution of the LSB disk is best explained by the accretion of
gas-rich LSB dwarf galaxies.Comment: 17 pages, 16 figures, 4 tables; accepted to the Astrophysical Journa
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