59 research outputs found
A consistent thermodynamics of the MHD wave-heated two-fluid solar wind
International audienceWe start our considerations from two more recent findings in heliospheric physics: One is the fact that the primary solar wind protons do not cool off adiabatically with distance, but appear to be heated. The other one is that secondary protons, embedded in the solar wind as pick-up ions, behave quasi-isothermal at their motion to the outer heliosphere. These two phenomena must be physically closely connected with each other. To demonstrate this we solve a coupled set of enthalpy flow conservation equations for the two-fluid solar wind system consisting of primary and secondary protons. The coupling of these equations comes by the heat sources that are relevant, namely the dissipation of MHD turbulence power to the respective protons at the relevant dissipation scales. Hereby we consider both the dissipation of convected turbulences and the dissipation of turbulences locally driven by the injection of new pick-up ions into an unstable mode of the ion distribution function. Conversion of free kinetic energy of freshly injected secondary ions into turbulence power is finally followed by partial reabsorption of this energy both by primary and secondary ions. We show solutions of simultaneous integrations of the coupled set of differential thermodynamic two-fluid equations and can draw interesting conclusions from the solutions obtained. We can show that the secondary proton temperature with increasing radial distance asymptotically attains a constant value with a magnitude essentially determined by the actual solar wind velocity. Furthermore, we study the primary proton temperature within this two-fluid context and find a polytropic behaviour with radially and latitudinally variable polytropic indices determined by the local heat sources due to dissipated turbulent wave energy. Considering latitudinally variable solar wind conditions, as published by McComas et al. (2000), we also predict latitudinal variations of primary proton temperatures at large solar distances
Interplanetary scintillation and pulsar pulse statistics
The effect of interplanetary plasma on pulsed pulsar radiation passing
through is considered. The pulses of two rotating radio transients (J0609+16,
J1132+25) and a pulsar (B0320+39) detected on the Large Phased Array (Pushchino
observatory) were analyzed. It is shown that in observations at the frequency
of 111 MHz, on elongations of 20o-40o, both an increase and a decrease in the
number of received pulses are observed. The change in the number of pulses is
explained by the distortion of the energy distribution of pulses due to
interplanetary scintillation. These changes in the number of observed pulses
are in qualitative agreement with the expected dependence of the scintillation
index on the observed sources elongation. Analytical expressions are obtained
that allow estimating the effective modulation index from observations of
individual pulses for the power distribution of pulses by energy.Comment: accepted to MNRAS, 5 pages, 3 figure
Study of Bright Compact Radio Sources of the Northern Hemisphere at the frequency of 111 MHz
The search for compact components of strong ( Jy at 102.5 MHz)
discrete radio sources from the Pushchino catalogue was carried out using the
method of interplanetary scintillation. A total of 3620 sources were examined,
and 812 of them were found to compact (scintillating) components. Estimates of
fluctuations of the flux density of these compact components were derived from
the scintillation index () corresponding to an elongation of .
The angular size and compactness of 178 sources with compact components were
estimated. Scintillation indices of sources corresponding to the compact
component () and flux densities of compact components were determined.
It was demonstrated that slow variations of the spatial distribution of
interplanetary plasma, which are related to the 11-year cycle of solar
activity, may exert a systematic influence on the estimates of angular sizes of
sources. Coefficients compensating the deviation from the spherical symmetry of
solar wind in the estimates of angular sizes were found using the coefficient
of asymmetry of the statistical distribution of intensity fluctuations. The
study of correlations between the parameters of sources in the sample revealed
that the maximum value of the scintillation index decreases as the integrated
flux increases, while the angular size has no marked dependence on the
integrated flux.Comment: published in Astronomy Report, translated by Yandex translator with
correction of scientific lexis, 16 pages, 6 figures, 3 table, appendi
Detection of Five New RRATs at 111 MHz
Results of 111-MHz monitoring observations carried out on the Big Scanning
Antenna of the Pushchino Radio Astronomy Observatory during September 1-28,
2015 are presented. Fifty-four pulsating sources were detected at declinations
. Forty-seven of these are known pulsars, five are new
sources, and two are previously discovered transients. Estimates of the peak
flux densities and dispersion measures are presented or all these sources.Comment: published in Astronomy Report, translated by Yandex translator with
correction of scientific lexis, 8 pages, 2 figures, 3 table
Theory of Parabolic Arcs in Interstellar Scintillation Spectra
Our theory relates the secondary spectrum, the 2D power spectrum of the radio
dynamic spectrum, to the scattered pulsar image in a thin scattering screen
geometry. Recently discovered parabolic arcs in secondary spectra are generic
features for media that scatter radiation at angles much larger than the rms
scattering angle. Each point in the secondary spectrum maps particular values
of differential arrival-time delay and fringe rate (or differential Doppler
frequency) between pairs of components in the scattered image. Arcs correspond
to a parabolic relation between these quantities through their common
dependence on the angle of arrival of scattered components. Arcs appear even
without consideration of the dispersive nature of the plasma. Arcs are more
prominent in media with negligible inner scale and with shallow wavenumber
spectra, such as the Kolmogorov spectrum, and when the scattered image is
elongated along the velocity direction. The arc phenomenon can be used,
therefore, to constrain the inner scale and the anisotropy of scattering
irregularities for directions to nearby pulsars. Arcs are truncated by finite
source size and thus provide sub micro arc sec resolution for probing emission
regions in pulsars and compact active galactic nuclei. Multiple arcs sometimes
seen signify two or more discrete scattering screens along the propagation
path, and small arclets oriented oppositely to the main arc persisting for long
durations indicate the occurrence of long-term multiple images from the
scattering screen.Comment: 22 pages, 11 figures, submitted to the Astrophysical Journa
The effects of a kappa-distribution in the heliosheath on the global heliosphere and ENA flux at 1 AU
We investigate heliosheath energetic neutral atom (ENA) fluxes at keV
energies, by assuming that the heliosheath proton distribution can be
approximated by a kappa-distribution. The choice of the kappa parameter derives
from observational data of the solar wind (SW). This has direct applications to
the upcoming IBEX mission. We will look at all-sky ENA maps within the IBEX
energy range (10 eV to 6 keV), as well as ENA energy spectra in several
directions. We find that the use of kappa, as opposed to a Maxwellian, gives
rise to greatly increased ENA fluxes above 1 keV, while medium energy fluxes
are somewhat reduced. We show how IBEX data can be used to estimate the
spectral slope in the heliosheath, and that the use of kappa reduces the
differences between ENA maps at different energies. We also investigate the
effect introducing a kappa-distribution has on the global interaction between
the SW and the local interstellar medium (LISM), and find that there is
generally an increase in energy transport from the heliosphere into the LISM,
due to the modified profile of ENA's energies. This results in a termination
shock that moves out by 4 AU, a heliopause that moves in by 9 AU and a bow
shock 25 AU farther out, in the nose direction
Pulsar microstructure and its quasi-periodicities with the S2 VLBI system at a resolution of 62.5 nanoseconds
We report on a study of microstructure and its quasi-periodicities of three
pulsars at 1.65 GHz with the S2 VLBI system at a resolution of 62.5 ns, by far
the highest for any such statistical study yet. For PSR B1929+10 we found in
the average cross-correlation function (CCF) broad microstructure with a
characteristic timescale of 95+-10 mcs and confirmed microstructure with
characteristic timescales between 100 and 450 mcs for PSRs B0950+08 and
B1133+16. On a finer scale PSRs B0950+08, B1133+16 (component II) and B1929+10
show narrow microstructure with a characteristic timescale in the CCFs of ~10
mcs, the shortest found in the average CCF or autocorrelation function (ACF)
for any pulsar, apart perhaps for the Crab pulsar. Histograms of microstructure
widths are skewed heavily toward shorter timescales but display a sharp cutoff.
The shortest micropulses have widths between 2 and 7 mcs. No nanopulses or
unresolved pulse spikes were detected. Cross-power spectra of single pulses
show a large range of complexity with single spectral features representing
classic quasi-periodicities and broad and overlapping features with essentially
no periodicities at all. Significant differences were found for the two
components of PSR B1133+16 in every aspect of our statistical analysis of
micropulses and their quasi-periodicities. Asymmetries in the magnetosphere and
the hollow cone of emission above the polar cap of the neutron star may be
responsible for these differences.Comment: 18 pages, 11 figures, 3 tables, A&A, 2001, accepte
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