It is shown that two circularly polarised Alfven waves that propagate along the ambient magnetic field in an uniform plasma trigger non oscillating electromagnetic field components when they cross each other. The non-oscilliating field components can
accelerate ions and electrons with great efficiency. This work is based on particle-in-cell (PIC) numerical simulations and on analytical non-linear computations. The analytical computations are done for two counter-propagating monochromatic waves. The simulations are done with monochromatic waves and with wave packets. The simulations show parallel electromagnetic fields consistent with the theory, and they show that the particle acceleration result in plasma cavities and, if the waves amplitudes are high enough, in ion beams. These acceleration processes could be relevant in space plasmas. For instance, they could be at work in the auroral zone and in the radiation belts of the Earth magnetosphere. In particular, they may explain the origin of the deep plasma cavities observed in the Earth auroral zone.
The six known highly dispersed fast radio bursts are attributed to extragalactic radio sources, of unknown origin but extremely energetic. We propose here a new explanation - not requiring an extreme release of energy - involving a body (planet, aste
roid, white dwarf) orbiting an extragalactic pulsar. We investigate a theory of radio waves associated to such pulsar-orbiting bodies. We focus our analysis on the waves emitted from the magnetic wake of the body in the pulsar wind. After deriving their properties, we compare them with the observations of various transient radio signals in order to see if they could originate from pulsar-orbiting bodies. The analysis is based on the theory of Alfven wings: for a body immersed in a pulsar wind, a system of two stationary Alfven waves is attached to the body, provided that the wind is highly magnetized. When destabilized through plasma instabilities, Alfven wings can be the locus of strong radio sources convected with the pulsar wind. Assuming a cyclotron maser instability operating in the Alfven wings, we make predictions about the shape, frequencies and brightness of the resulting radio emissions. Because of the beaming by relativistic aberration, the signal is seen only when the companion is perfectly aligned between its parent pulsar and the observer, as for occultations. For pulsar winds with a high Lorentz factor, the whole duration of the radio event does not exceed a few seconds, and it is composed of one to four peaks lasting a few milliseconds each, detectable up to distances of several Mpc. The Lorimer burst, the three isolated pulses of PSR J1928+15, and the recently detected fast radio bursts are all compatible with our model. According to it, these transient signals should repeat periodically with the companions orbital period. The search of pulsar-orbiting bodies could be an exploration theme for new- or next-generation radio telescopes.
We investigate whether one or many companions are orbiting the extremely intermittent pulsar PSR B1931+24. We constrained our analysis on previous observations of eight fundamental properties of PSR B1931+24. The most puzzling properties are the inte
rmittent nature of the pulsars activity, with active and quiet phases that alternate quasi-periodically; the variation of the slowing-down rate of its period between active and quiet phases; and because there are no timing residuals, it is highly unlikely that the pulsar has a massive companion. Here, we examine the effects that one putative companion immersed in the magnetospheric plasma or the wind of the pulsar might have, as well as the associated electric current distribution. We analysed several possibilities for the distance and orbit of this hypothetical companion and the nature of its interaction with the neutron star. We show that if the quasi-periodic behaviour of PSR B1931+24 was caused by a companion orbiting the star with a period of 35 or 70 days, the radio emissions, usually considered to be those of the pulsar would in that specific case be emitted in the companions environment. We analysed four possible configurations and conclude that none of them would explain the whole set of peculiar properties of PSR 1931+24. We furthermore considered a period 70 days for the precession of the periastron associated to an orbit very close to the neutron star. This hypothesis is analysed in a companion paper.
We investigate the electromagnetic interaction of a relativistic stellar wind with a planet or a smaller body in orbit around a pulsar. This may be relevant to objects such as PSR B1257+12 and PSR B1620-26 that are expected to hold a planetary system
, or to pulsars with suspected asteroids or comets. Most models of pulsar winds predict that, albeit highly relativistic, they are slower than Alfven waves. In that case, a pair of stationary Alfven waves, called Alfven wings (AW), is expected to form on the sides of the planet. The wings expand far into the pulsars wind and they could be strong sources of radio emissions. The Alfven wings would cause a significant drift over small bodies such as asteroids and comets.
In the Earth auroral zone, the electron acceleration by Alfven waves is sometimes a precursor of the non-propagating acceleration structures. In order to investigate how Alfven waves could generate non-propagating electric fields, a series of simulat
ions of counter-propagating waves in a uniform plasma is presented. The waves (initially not configured to accelerate particles) propagate along the ambient magnetic field direction. It is shown that non propagating electric fields are generated at the locus of the Alfven waves crossing. These electric fields have a component orientated along the direction of the ambient magnetic field, and they generate acceleration and a significant perturbation of the plasma density. The non-linear interaction of down and up-going Alfven waves might be a cause of plasma density fluctuations (with gradients along the magnetic field) on a scale comparable to those of the Alfven wavelengths.
The acceleration of electrons at 1-10 keV energies is the cause of the polar aurora displays, and an important factor of magnetic energy transfer from the solar wind to the Earth. Two main families of acceleration processes are observed: those based
on coherent quasi-static structures called double layers, and those based of the propagation of Alfven Waves (AW). This paper is a review of the Alfvenic acceleration processes, and of their role in the global dynamics of the auroral zone.
Interstellar dark clouds are the sites of star formation. Their main component, dihydrogen, exists under two states, ortho and para. H2 is supposed to form in the ortho:para ratio (OPR) of 3:1 and to subsequently decay to almost pure para-H2 (OPR <=
0.001). Only if the H2 OPR is low enough, will deuteration enrichment, as observed in the cores of these clouds, be efficient. The second condition for strong deuteration enrichment is the local disappearance of CO, which freezes out onto grains in the core formation process. We show that this latter condition does not apply to DCO+, which, therefore, should be present all over the cloud. We find that an OPR >= 0.1 is necessary to prevent DCO+ large-scale apparition. We conclude that the inevitable decay of ortho-H2 sets an upper limit of ~6 million years to the age of starless molecular clouds under usual conditions.
We use the Excursion Set formalism to compute the properties of the halo mass distribution for a stochastic barrier model which encapsulates the main features of the ellipsoidal collapse of dark matter halos. Non-markovian corrections due to the shar
p filtering of the linear density field in real space are computed with the path-integral technique introduced by Maggiore & Riotto (2010). Here, we provide a detailed derivation of the results presented in Corasaniti & Achitouv (2011) and extend the mass function analysis to higher redshift. We also derive an analytical expression for the linear halo bias. We find the analytically derived mass function to be in remarkable agreement with N-body simulation data from Tinker et al. (2008) with differences smaller than ~5% over the range of mass probed by the simulations. The excursion set solution from Monte Carlo generated random walks shows the same level of agreement, thus confirming the validity of the path-integral approach for the barrier model considered here. Similarly the analysis of the linear halo bias shows deviations no greater than 20%. Overall these results indicate that the Excursion Set formalism in combination with a realistic modeling of the conditions of halo collapse can provide an accurate description of the halo mass distribution.
A planet orbiting around a pulsar would be immersed in an ultra-relativistic under-dense plasma flow. It would behave as a unipolar inductor, with a significant potential drop along the planet. As for Io in Jupiters magnetosphere, there would be two
stationary Alfven waves, the Alfven wings (AW), attached to the planet. The AW would be supported by strong electric currents, in some circumstances comparable to those of a pulsar. It would be a cause of powerful radio waves emitted all along the AW, and highly collimated through relativistic aberration. There would be a chance to detect these radio-emissions from Earth. The emission would be pulses as for ordinary pulsars; their occurrence would depend on the planet-star-observer angle. These results are still preliminary, further work needs to be done.
We investigate the electromagnetic interaction of a relativistic stellar wind with small bodies in orbit around the star. Based on our work on the theory of Alfven wings to relativistic winds presented in a companion paper, we estimate the force exer
ted by the associated current system on orbiting bodies and evaluate the resulting orbital drift. This Alfvenic structure is found to have no significant influence on planets or smaller bodies orbiting a millisecond pulsar. %influence on the orbit of bodies around a millisecond pulsar. On the timescale of millions of years, it can however affect the orbit of bodies with a diameter of 100 kilometres around standard pulsars with a period $P sim $1 s and a magnetic field $B sim 10^{8}$ T. Kilometer-sized bodies experience drastic orbital changes on a timescale of $10^4$ years.
