Pulsar Polarization Research Articles

Quasi-linear theory of Cherenkov-drift instability: Application for radio pulsars

We present a plasma model for formation of discontinuous position-angle curves observed in some radio pulsar profiles. The model is based on the polarization properties of radio waves excited by Cherenkov-drift instability develop- ing in pulsar magnetospheres. The radiation is confined in a cone of emission and consists of two orthogonally polarized waves. Examination of a quasi-linear stage of Cherenkov-drift instability shows that the excitation mechanism provides the modes with dierent spectral energy densities depending on the direction of k. As a pulsar rotates, an observer's sight-line track crosses dierent mode-predominated areas on the base of the emission cone. Transition of the sight-line track from one mode-predominated area to another results in the formation of pulsar polarization fluctuations observed in polarization angle distribution displays and average waveforms.

Scintillation‐induced Circular Polarization in Pulsars and Quasars

We present a physical interpretation for the generation of circular polarization resulting from the propagation of radiation through a magnetized plasma in terms of a rotation measure gradient, or Faraday wedges. Criteria for the observability of scintillation-induced circular polarization are identified. Application of the theory to the circular polarization in pulsars and compact extragalactic sources is discussed.

Multifrequency polarimetry of 300 radio pulsars

Polarimetric observations of 300 pulsars have been conducted with the 76-m Lovell telescope at Jodrell Bank at radio frequencies centred around 230, 400, 600, 920, 1400 and 1600 MHz. More than half of the pulsars have no previously published polarization profiles and this compilation represents about three times the sum of all previously published pulsar polarization data. A selection of integrated polarization profiles is provided. Tables of pulse widths and the degree of both linear and circular polarization are given for all pulsars, and these act as an index for all the data, which are available by anonymous ftp in numerical and graphical form.

Effelsberg multifrequency pulsar polarimetry

A sample of 64 well-calibrated pulsar polarization profiles measured at cm-wavelengths with the Effelsberg radio telescope is presented. All profiles were measured using an adding and a multiplying polarimeter which enables polarimetry over wide-bandwidths. Gain imbalances introduced by the active components in the signal path, as well as system imperfections, alter the polarization state of the incoming radiation. An analysis of the signal path of those devices is presented, together with a dynamic calibration procedure introduced to eliminate the instrumental errors. The results were used to trace the location of the radiating region in pulsar magnetospheres at high frequencies.

Pulsar Polarization, Emission, and Beaming

AbstractThis paper discusses observational and analytical questions pertaining to the pulsar emission problem. A short outline of the area is given for those new to the subject. Some of the literature pertinent to pulsar polarization, emission and beaming, which has appeared over about the last five years is mentioned. There is a short discussion of efforts to carry out polarimetric observations of higher quality, and finally, there is a short discussion of recent work by the author and her colleagues.

Individual Pulse Polarization of Pulsars at Low Frequencies

AbstractThis paper presents the results of the measurements of linear polarization characteristics of individual pulses at frequencies 40, 60 and 103 MHz for 10 strong pulsars. We have measured total intensity, linear polarization percentage and angle along the pulse window and obtained distribution displays for these data.Two orthogonal polarization modes are common features in the radiation of pulsars at low frequency. The energy ratio of these two modes can change significantly between different frequencies. The linear polarisation percentage has a general tendency to increase at low frequencies, but by very different factors for different components of the integrated intensity profile. The relationship between the polarization properties of PSR 0943+10 and its mode changing behaviour was studied. It is shown that the energy ratio and the frequency of occurence of two polarization modes change simultaneously with changes in the integrated intensity profile.

Polarization and Faraday rotation measurements of southern pulsars

Polarization and Faraday rotation measurements of southern pulsars

Mean pulse polarization of southern pulsars at 1560 MHz

Mean pulse total intensity and polarization data at 1560 MHz are presented for 45 southern pulsars. The observations were made during 1988 at Parkes using a filter-bank polarimeter system. The results are discussed in terms of the rotating vector model for pulse polarization. Notable results include a highly polarized interpulse pulsar and several pulsars with very wide mean pulse profiles

Modeling of Pulsar Polarization Properties

AbstractIn the popularly accepted empirical model for pulsar emission, bunches of charged particles traveling along open field lines near the magnetic pole emit curvature radiation. Such radiation is linearly polarized. Most of the radiation is assumed to be emitted from a ring shaped region centered on the pole (the hollow cone model). We have calculated the expected average polarization using this model and find them to be in disagreement with observations. The addition of a second ring inside the first with orthogonal polarization solves this problem. This new model explains other observed features of pulsar emission including discontinuities in position-angle profiles and multicomponent profiles. Plasma interactions might account for a second ring.

Pulsar polarization measurements and the nonsymmetric gravitational theory.

Because of the breakdown of the Einstein equivalence principle in the nonsymmetric gravitational theory (NGT) of Moffat, orthogonally polarized electromagnetic waves can propagate at different velocities in a gravitational field. Moffat has proposed that galactic dark matter, in the form of cosmions, may act as a significant source of gravity in the NGT. We discuss how observations of the highly polarized radiation from distant pulsars could provide significant limits on the strength of the coupling of cosmions in the NGT.

A relativistic model of pulsar polarization

The rotating vector model of pulsar polarization of Radhakrishnan and Cooke (1969) is extended here to include first-order special relativistic effects. The model predicts that the centroid of the position angle curve arrives later than the centroid of the intensity profile by 4r/c, where r is the emission radius. Application of the model to pulsars with well ordered position-angle swings and periods between 0.06 and 3.7 s give emission radii of not more than 2000 km for 0.43 and 1.4 GHz. Symmetry-breaking effects of the corotation velocity may help explain a general asymmetry found in pulsar intensity profiles and may strongly affect the intensity profiles of short-period pulsars. 66 refs.

Triplicity of pulsar profiles and orthogonal polarization modes

It is assumed that pulsar emission is composed of two distinct beams originating in the magnetosphere at widely separated locations. It is shown that if one of the beams arises in a region where the magnetic field lines are distorted from dipolar form due to the pulsar rotation then the polarization vectors of this beam are not, in general, parallel to the polarization vectors of the other beam which originates in an undistorted field region. In many geometrical situations, the polarization vectors of the two distinct beams can be mutually quasi-perpendicular. Therefore, the existence of these two beams of pulsar emission is equivalent to the existence of two superposed orthogonal polarization modes. It is argued that different polarization modes correspond to the core and conal pulsar emission. The main polarization mode associated with core emission originates close to the star, while the other mode associated with conal emission originates much farther from the star, in the region where the curvature of the field lines is dominated by the toroidal component of the pulsar magnetic field. 17 references.

Pulsar polarization fluctuations. I - 1404 MHz statistical summaries. II -800 MHz statistical summaries

view Abstract Citations (196) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pulsar polarization fluctuations. I. 1404 MHz statistical summaries. Stinebring, D. R. ; Cordes, J. M. ; Rankin, J. M. ; Weisberg, J. M. ; Boriakoff, V. Abstract Individual-pulse polarization observations of 11 strong low-dispersion pulsars obtained at 1404 MHz using the 305-m Arecibo telescope during October, 1981 are reported; four pulsars were observed simultaneously at 800 MHz using the 92-m NRAO telescope at Green Bank, West Virginia. The results are presented graphically as distribution displays and polarization waveforms and compared with published data obtained at lower frequencies. Depolarization is observed at high frequencies and attributed to instantaneous superposition of nearly 100-percent orthogonally polarized radiation, which is found at both high and low frequencies (430-1404 MHz). These findings suggest that most pulsar emission occurs in one of the orthogonal polarization modes. Publication: The Astrophysical Journal Supplement Series Pub Date: June 1984 DOI: 10.1086/190954 Bibcode: 1984ApJS...55..247S Keywords: Polarization Characteristics; Pulsars; Radio Astronomy; Statistical Analysis; Angular Distribution; Circular Polarization; Instrument Errors; Linear Polarization; Waveforms; Astrophysics; Pulsars:Radio Polarization; Radio Polarization:Pulsars full text sources ADS | data products SIMBAD (11) Related Materials (1) Part 2: 1984ApJS...55..279S

Pulsar polarization as a direct consequence of the emission process

On presente un calcul des proprietes de polarisation d'un rayonnement emis par une particule acceleree par la courbe de la trajectoire pre-determinee et parallele a la vitesse instantanee

Pulsar polarization - Weak sources and emission features at 430 MHz

Pulsar polarization - Weak sources and emission features at 430 MHz

Pulsar Polarization

Over ten years ago Radhakrishnan and his coworkers in Australia detected a smooth variation of the electric vector through 90° during the brief pulses from the Vela pulsar. This observation led to the hypothesis that pulsar radiation is beamed along a magnetic pole. While subsequent observations gave ample support to this model, we find that less than half of the pulsars have average profiles which are consistent with the magnetic pole hypothesis. Statistical analyses of individual pulse polarization data now reveal that the average profiles obscure the basic nature of linear polarization in pulsars: two orthogonal modes are typically present, and individually these modes agree with the magnetic pole model. We explain the occurrence of orthogonal modes by a simple geometry for the polarized subpulse beam in relation to the magnetic axis. Theoretical models for subpulse polarization invoke both a combination of emission mechanism effects and propagation effects. We conclude with directions for further research.

Coronal Faraday rotation during solar occultation of PSR0525 + 21

The apparent position of the pulsar PSR0525 + 21 is within 1.3° (4.72 R⊙) of the south solar pole on or about 13 June of each year. During these times of superior conjunction, the linearly polarised component of the pulsar radiation is subjected to an additional Faraday rotation due to the high electron density and strong magnetic field of the solar corona. We report here measurements of this coronal Faraday rotation in 1978 and 1979 at the 100-m radio telescope of the Max-Planck-Institut fur Radioastronomie in Effelsberg which compared pulsar polarisation profiles at λ =17.4 cm (f=1,720 MHz) for times before, during and after occultation by the Sun. A significant residual rotation measure, which exceeded the interstellar value, was observed both years at times close to that of minimum solar approach.

Plane of polarization rotation induced by a non-Minkowskian spacetime

Fermat's principle has been used to derive expressions for the curvature and torsion of the path of the electromagnetic radiation in a medium of refractive indexn (= function of space coordinates). Levi-Civita's notion of parallelism further, in conjunction with Brill's results (cf. reference in text) have enabled the derivation (1) of Einstein's formula for the deflection of light, and (2) an expression for the rotation of the plane of polarization, an entirely general relativistic effect, unaccountable in Newtonian physics. Finally, the idea is put forward that the observed rotation of polarization in pulsars might be a purely general relativistic effect due to the non-Minkowskian geometry around them.

Pulsar polarization fluctuations at 430 MHz with microsecond time resolution

view Abstract Citations (54) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pulsar polarization fluctuations at 430 MHz with microsecond time resolution. Cordes, J. M. ; Hankins, T. H. Abstract The polarization properties of PSRs 0950+08, 1133+16, 1919+21, and 2016+28 at 430 MHz are studied on the basis of data processed to yield a time resolution of 8 microsec. Distortion caused by interstellar dispersion is removed from the data, Stokes parameters are computed from the dispersion-free signals, average Stokes parameters are calculated by summing the Stokes parameters of individual pulses, and the autocorrelation functions of the Stokes parameters are obtained by fast Fourier transform techniques. The mean Stokes-parameter profiles for each pulsar are evaluated using a model that represents subpulses as unsteady-state stochastic modulations of a steady-state microstructure. It is found that the polarization exhibited in single pulses (i.e., that associated with subpulses or micropulses) can be described as either (1) a slow variation of the polarization state across pulse longitude or (2) occasional rapid transitions of the polarization state between two orthogonal states having opposite senses of circular polarization and position angles separated by 90 deg. Publication: The Astrophysical Journal Pub Date: December 1977 DOI: 10.1086/155702 Bibcode: 1977ApJ...218..484C Keywords: Microwave Emission; Polarization Characteristics; Pulsars; Signal Distortion; Circular Polarization; Cross Coupling; Data Processing; Fast Fourier Transformations; Interstellar Extinction; Ultrahigh Frequencies; Wave Dispersion; Astrophysics full text sources ADS | data products SIMBAD (4)

The effect of vacuum birefringence on the polarization of X-ray binaries and pulsars

In a strong magnetic field the vacuum becomes birefringent. This effect is especially important for pulsars at X-ray wavelengths. Any polarized X-ray emission from the surface of a magnetic neutron star becomes depolarized as it propagates through the magnetic field. The soft X-ray emission from AM Her, believed to be a magnetic white dwarf, may show about one radian of phase retardation. In this case, circular polarization of the X-ray flux would be a characteristic signature of vacuum birefringence.