Pisʹma v Astronomičeskij žurnal

Transonic (withMach numberMs   1) motion of a pulsar relative to the external medium can
help its compact pulsar wind nebula develop a double-torus X-ray morphology. The double-torus structure
can reverberate as a whole under the dynamic pressure of the external flow. For a flow aligned with the
symmetry axis of the nebula, the response of the double-torus is uniform in azimuth. For a misaligned
flow, the leeward sides of the tori respond with some delay relative to their windward sides. The delay can
cause a curious swaying in the short midsection of the leeward jet of the compact X-ray nebula. Within the
framework of the relativisticmagnetohydrodynamical model of a pulsar wind nebula we study the dynamics
of the nebular outflows contributing to the swaying of the jet. When applied to the Vela X-ray nebula, the
model allows us to naturally relate two distinct phenomena, the swaying of the bright midsection of the Vela
lee jet and the reverberation of its double-torus.

We have performed a comparative analysis of the angles β between the rotation axis and the
magnetic moment in three groups of radio pulsars: sources inwhich only radio emission is observed, pulsars
with detected X-ray emission, and radio-loud gamma-ray pulsars. For this purpose, we have calculated the
values of the angle β separately for objects from each group by two differentmethods. It has turned out that
in pulsars with hard emission themean values of this angle (28.2◦ and 28.8◦) are greater than those for quiet
radio pulsars (12.9◦). However, using the Kolmogorov–Smirnov test, we have shown that the revealed
difference is insignificant with a high probability. Consequently, the structures of the magnetospheres in the
three groups of pulsars considered do not differ greatly, while their difference is attributable to the magnetic
field strength on the light cylinder that switches on the hard nonthermal emission mechanism in pulsars
with detected X-ray and/or gamma-ray emission but is not enough for this in quiet radio pulsars in the
hard ranges.

Using a relativistic plasma with an isotropic monoenergetic distribution of electrons and
positrons as an example, we show that in the maser regime the maximum possible amplification of
synchrotron radiation at a distance of one wavelength is achieved in a medium where the magnetic energy
density is of the order of the particle energy density. This ratio of the energy densities corresponds to a
(Harris-type) current sheet. We have obtained an electron Lorentz factor of 350 and a magnetic field
strength of 10 kG in the maser radio emission region for the Crab pulsar. Our estimate suggests that
the optical and coherent radio emissions of the object originate from one synchrotron source in the form of
a current sheet. The diameter of the source must exceed the light-cylinder radius approximately by a factor
of 6 for the maser wave field to interact with particles in the linear regime, in particular, to keep its phase
velocity higher than the speed of light in a vacuum—a necessary condition for the synchrotron instability.

Superbursts of neutron stars are rare but powerful events explained by the explosive burning
of carbon in the deep layers of the outer envelope of the star. In this paper we perform a simulation of
superbursts and propose a simple method for describing the neutrino stage of their cooling, as well as a
method for describing the evolution of the burst energy on a scale of several months. We note a universal
relation for the temperature distribution in the burnt layer at its neutrino cooling stage, as well as the
unification of bolometric light curves and neutrino heat loss rates for deep and powerful bursts. We point
out the possibility of long-term retention of the burst energy in the star’s envelope. The results can be useful
for interpretation of superburst observations.