3,432 research outputs found
An algorithm for solving the pulsar equation
We present an algorithm of finding numerical solutions of pulsar equation.
The problem of finding the solutions was reduced to finding expansion
coefficients of the source term of the equation in a base of orthogo- nal
functions defined on the unit interval by minimizing a multi-variable mismatch
function defined on the light cylinder. We applied the algorithm to Scharlemann
& Wagoner boundary conditions by which a smooth solu- tion is reconstructed
that by construction passes success- fully the Gruzinov's test of the source
function exponent.Comment: 4 pages, 4 figures, accepted for publication in ApSS (a shortened
version of the previous one
Electric field representation of pulsar intensity spectra
Pulsar dynamic spectra exhibit high visibility fringes arising from
interference between scattered radio waves. These fringes may be random or
highly ordered patterns, depending on the nature of the scattering or
refraction. Here we consider the possibility of decomposing pulsar dynamic
spectra -- which are intensity measurements -- into their constituent scattered
waves, i.e. electric field components. We describe an iterative method of
achieving this decomposition and show how the algorithm performs on data from
the pulsar B0834+06. The match between model and observations is good, although
not formally acceptable as a representation of the data. Scattered wave
components derived in this way are immediately useful for qualitative insights
into the scattering geometry. With some further development this approach can
be put to a variety of uses, including: imaging the scattering and refracting
structures in the interstellar medium; interstellar interferometric imaging of
pulsars at very high angular resolution; and mitigating pulse arrival time
fluctuations due to interstellar scattering.Comment: 7 Pages, 2 Figures, revised version, accepted by MNRA
Coherent network analysis for continuous gravitational wave signals in a pulsar timing array: Pulsar phases as extrinsic parameters
Supermassive black hole binaries are one of the primary targets for
gravitational wave searches using pulsar timing arrays. Gravitational wave
signals from such systems are well represented by parametrized models, allowing
the standard Generalized Likelihood Ratio Test (GLRT) to be used for their
detection and estimation. However, there is a dichotomy in how the GLRT can be
implemented for pulsar timing arrays: there are two possible ways in which one
can split the set of signal parameters for semi-analytical and numerical
extremization. The straightforward extension of the method used for continuous
signals in ground-based gravitational wave searches, where the so-called pulsar
phase parameters are maximized numerically, was addressed in an earlier paper
(Wang et al. 2014). In this paper, we report the first study of the performance
of the second approach where the pulsar phases are maximized semi-analytically.
This approach is scalable since the number of parameters left over for
numerical optimization does not depend on the size of the pulsar timing array.
Our results show that, for the same array size (9 pulsars), the new method
performs somewhat worse in parameter estimation, but not in detection, than the
previous method where the pulsar phases were maximized numerically. The origin
of the performance discrepancy is likely to be in the ill-posedness that is
intrinsic to any network analysis method. However, scalability of the new
method allows the ill-posedness to be mitigated by simply adding more pulsars
to the array. This is shown explicitly by taking a larger array of pulsars.Comment: 30 pages, 11 figures, revised version, published in Ap
The optimal schedule for pulsar timing array observations
In order to maximize the sensitivity of pulsar timing arrays to a stochastic
gravitational wave background, we present computational techniques to optimize
observing schedules. The techniques are applicable to both single and
multi-telescope experiments. The observing schedule is optimized for each
telescope by adjusting the observing time allocated to each pulsar while
keeping the total amount of observing time constant. The optimized schedule
depends on the timing noise characteristics of each individual pulsar as well
as the performance of instrumentation. Several examples are given to illustrate
the effects of different types of noise. A method to select the most suitable
pulsars to be included in a pulsar timing array project is also presented.Comment: 16 pages, 6 figures, accepted by MNRA
Growth rates of the Weibel and tearing mode instabilities in a relativistic pair plasma
We present an algorithm for solving the linear dispersion relation in an
inhomogeneous, magnetised, relativistic plasma. The method is a generalisation
of a previously reported algorithm that was limited to the homogeneous case.
The extension involves projecting the spatial dependence of the perturbations
onto a set of basis functions that satisfy the boundary conditions (spectral
Galerkin method). To test this algorithm in the homogeneous case, we derive an
analytical expression for the growth rate of the Weibel instability for a
relativistic Maxwellian distribution and compare it with the numerical results.
In the inhomogeneous case, we present solutions of the dispersion relation for
the relativistic tearing mode, making no assumption about the thickness of the
current sheet, and check the numerical method against the analytical
expression.Comment: Accepted by PPC
- âŠ