1,375,435 research outputs found
Scattering and Diffraction in Magnetospheres of Fast Pulsars
We apply a theory of wave propagation through a turbulent medium to the
scattering of radio waves in pulsar magnetospheres. We find that under
conditions of strong density modulation the effects of magnetospheric
scintillations in diffractive and refractive regimes may be observable. The
most distinctive feature of the magnetospheric scintillations is their
independence on frequency.
Results based on diffractive scattering due to small scale inhomogeneities
give a scattering angle that may be as large as 0.1 radians, and a typical
decorrelation time of seconds.
Refractive scattering due to large scale inhomogeneities is also possible,
with a typical angle of radians and a correlation time of the order
of seconds. Temporal variation in the plasma density may also result
in a delay time of the order of seconds. The different scaling of the
above quantities with frequency may allow one to distinguish the effects of
propagation through a pulsar magnetosphere from the interstellar medium. In
particular, we expect that the magnetospheric scintillations are relatively
more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur
Linear and Nonlinear Evolution and Diffusion Layer Selection in Electrokinetic Instability
In the present work fournontrivial stages of electrokinetic instability are
identified by direct numerical simulation (DNS) of the full
Nernst-Planck-Poisson-Stokes (NPPS) system: i) The stage of the influence of
the initial conditions (milliseconds); ii) 1D self-similar evolution
(milliseconds-seconds); iii) The primary instability of the self-similar
solution (seconds); iv) The nonlinear stage with secondary instabilities. The
self-similar character of evolution at intermediately large times is confirmed.
Rubinstein and Zaltzman instability and noise-driven nonlinear evolution to
over-limiting regimes in ion-exchange membranes are numerically simulated and
compared with theoretical and experimental predictions. The primary instability
which happens during this stage is found to arrest self-similar growth of the
diffusion layer and specifies its characteristic length as was first
experimentally predicted by Yossifon and Chang (PRL 101, 254501 (2008)). A
novel principle for the characteristic wave number selection from the
broadbanded initial noise is established.Comment: 13 pages, 8 figure
GRB Flares: UV/Optical Flaring (Paper I)
We present a new algorithm for the detection of flares in gamma-ray burst
(GRB) light curves and use this algorithm to detect flares in the UV/optical.
The algorithm makes use of the Bayesian Information Criterion (BIC) to analyze
the residuals of the fitted light curve, removing all major features, and to
determine the statistically best fit to the data by iteratively adding
additional `breaks' to the light curve. These additional breaks represent the
individual components of the detected flares: T_start, T_stop, and T_peak. We
present the detection of 119 unique flaring periods detected by applying this
algorithm to light curves taken from the Second Swift Ultraviolet/Optical
Telescope (UVOT) GRB Afterglow Catalog. We analyzed 201 UVOT GRB light curves
and found episodes of flaring in 68 of the light curves. For those light curves
with flares, we find an average number of ~2 flares per GRB. Flaring is
generally restricted to the first 1000 seconds of the afterglow, but can be
observed and detected beyond 10^5 seconds. More than 80% of the flares detected
are short in duration with Delta t/t of < 0.5. Flares were observed with flux
ratios relative to the underlying light curve of between 0.04 to 55.42. Many of
the strongest flares were also seen at greater than 1000 seconds after the
burst.Comment: Submitted to ApJ. 20 pages (including 8 figures and 1 table
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