On the thermal effects on radio waves propagating in the pulsar magnetosphere

Thermal effects on the properties of four electromagnetic waves propagating in the pulsar magnetosphere are analysed. It is shown that thermal effects change only quantitatively the dispersion properties of superluminal ordinary O-mode freely escaping the pulsar magnetosphere; whereas properties of the extraordinary X-mode remain unchanged. The research shows that for two subluminal waves propagating along magnetic field lines thermal effects result in essential absorption. However, this attenuation occurs at considerable distances from the neutron star, and there is no doubt of their existence.

Jiamusi pulsar observations

Aims. Most pulsar nulling observations have been conducted at frequencies lower than 1400 MHz. We aim to understand the nulling behaviors of pulsars at relatively high frequencies, and to decipher whether or not nulling is caused by a global change in the pulsar magnetosphere. Methods. We used the Jiamusi 66 m telescope to observe 20 bright pulsars at 2250 MHz with unprecedented lengths of time. We estimated the nulling fractions of these pulsars, and identified the null and emission states of the pulses. We also calculated the nulling degrees and scales of the emission-null pairs to describe the distributions of emission and null lengths. Results. Three pulsars, PSRs J0248+6021, J0543+2329, and J1844+00, are found to null for the first time. The details of null-to-emission and emission-to-null transitions within the pulse window are observed for the first time for PSR J1509+5531, which is a low-probability event. A complete cycle of long nulls with timescales of hours is observed for PSR J1709−1640. For most of these pulsars, the K-S tests of nulling degrees and nulling scales reject the hypothesis that null and emission are caused by random processes at high significance levels. Emission-null sequences of some pulsars exhibit quasi-periodic, low-frequency or featureless modulations, which might be related to different origins. During transitions between emission and null states, pulse intensities have diverse tendencies for variation. Significant correlations are found between respectively nulling fraction, nulling cadence, and nulling scale and the energy loss rate of the pulsars. Combined with the nulling fractions reported in the literature for 146 nulling pulsars, we find that statistically large nulling fractions are more tightly related to pulsar period than to characteristic age or energy-loss rate.

Excitation of the main giant pulses from the Crab pulsar

ABSTRACT A model for the source of microwave main giant pulses (GPs) from the Crab pulsar is proposed and partly investigated. Pulse excitation takes place in a relativistic pair plasma with a strong magnetic field through the beam pulse amplifier (BPA) mechanism, in which short noise pulses of a certain type are amplified by energetic electrons at the Cherenkov resonance, even without strong anisotropy in the distribution function. The wave gain is shown to be as high as with an instability of hydrodynamic type, and wave escaping from the excitation region into the pulsar magnetosphere may not involve significant attenuation. The basic parameters of the source which explains the observed characteristics of the GP electromagnetic bursts have been analysed and are consistent with accepted ideas about physical conditions in the pulsar magnetosphere. The BPA mechanism explains the important properties of the GPs, such as the extremely short pulse duration (extreme nanoshots), the extremely high brightness temperature of the radiation source, the formation of radiation in a wide frequency range, and the possibility of radiation reaching the periphery of the pulsar magnetosphere.

The permanent ellipticity of the neutron star in PSR J1023+0038

ABSTRACT A millisecond pulsar having an ellipticity, which is an asymmetric mass distribution around its spin-axis, could emit continuous gravitational waves, which have not been detected so far. An indirect way to infer such waves is to estimate the contribution of the waves to the spin-down rate of the pulsar. The transitional pulsar PSR J1023+0038 is ideal and unique for this purpose because this is the only millisecond pulsar for which the spin-down rate has been measured in both accreting and non-accreting states. Here, we infer, from our formalism based on the complete torque budget equations and the pulsar magnetospheric origin of observed γ-rays in the two states, that PSR J1023+0038 should emit gravitational waves due to a permanent ellipticity of the pulsar. The formalism also explains some other main observational aspects of this source in a self-consistent way. As an example, our formalism naturally infers the accretion disc penetration into the pulsar magnetosphere, and explains the observed X-ray pulsations in the accreting state using the standard and well-accepted scenario. This, in turn, infers the larger pulsar spin-down power in the accreting state, which, in our formalism, explains the observed larger γ-ray emission in this state. Exploring wide ranges of parameter values of PSR J1023+0038, and not assuming an additional source of stellar ellipticity in the accreting state, we find the misaligned mass quadrupole moment of the pulsar in the range of (0.92–1.88) × 1036 g cm2, implying an ellipticity range of (0.48–0.93) × 10−9.

Simulations of the radio polarization of a precessing pulsar PSR J1906+0746

ABSTRACT The recently constructed theory of radio wave propagation in the pulsar magnetosphere outlines the general aspects of the radio light curve and polarization formation. It allows us to describe general properties of mean profiles, such as the position angle of the linear polarization, and the circular polarization for the realistic structure of the pair creation region in the pulsar magnetosphere. In this work, we present an application of the radio wave propagation theory to the radio observations of pulsar PSR J1906+0746. This pulsar is particularly interesting because observations of relativistic spin precession in a binary system allow us to put strong constraints on its geometry. Because it is an almost orthogonal rotator, the pulsar allows us to observe both magnetic poles; as we show, this is crucial for testing the theory of radio wave propagation and obtaining constraints on the parameters of magnetospheric plasma. Our results show that plasma parameters are qualitatively consistent with theories of pair plasma production in polar cap discharges. Specifically, for PSR J1906+0746, we constrain the plasma multiplicity λ ∼ 103 and the Lorentz factor of secondary plasma γ ∼ a few hundred.

A novel approach for the analysis of the geometry involved in determining light curves of pulsars

ABSTRACT In this work, we introduce the use of the differential geometry Frenet–Serret equations to describe a magnetic line in a pulsar magnetosphere. These equations, which need to be solved numerically, fix the magnetic line in terms of their tangent, normal, and binormal vectors at each position, given assumptions on the radius of curvature and torsion. Once the representation of the magnetic line is defined, we provide the relevant set of transformations between reference frames; the ultimate aim is to express the map of the emission directions in the star corotating frame. In this frame, an emission map can be directly read as a light curve seen by observers located at a certain fixed angle with respect to the rotational axis. We provide a detailed step-by-step numerical recipe to obtain the emission map for a given emission process, and give a set of simplified benchmark tests. Key to our approach is that it offers a setting to achieve an effective description of the system’s geometry together with the radiation spectrum. This allows to compute multifrequency light curves produced by a specific radiation process (and not just geometry) in the pulsar magnetosphere, and intimately relates with averaged observables such as the spectral energy distribution.