scholarly journals Circular polarization in radio pulsar PSR B1451−68: coherent mode transitions and intrabeam interference

2020 ◽  
Vol 501 (2) ◽  
pp. 2156-2173
Author(s):  
J Dyks ◽  
P Weltevrede ◽  
C Ilie
Keyword(s):  
Radio Pulsar ◽  
Vector Model ◽  
Polarization Degree ◽  
Orthogonal Polarization ◽  
Polarization Angle ◽  
Phase Lag ◽  
Pulse Profile ◽  
Oscillation Phase ◽  
Leave No Trace ◽  
Mode Transitions

ABSTRACT The radio emission of pulsar B1451−68 contains two polarization modes of similar strength, which produce two clear orthogonal polarization angle tracks. When viewed on a Poincaré sphere, the emission is composed of two flux patches that rotate meridionally as a function of pulse longitude and pass through the Stokes V poles, which results in transitions between orthogonal polarization modes (OPMs). Moreover, the ratio of power in the patches is inversed once within the profile window. It is shown that the meridional circularization is caused by a coherent OPM transition (COMT) produced by a varying mode ratio at a fixed quarter-wave phase lag. The COMTs may be ubiquitous and difficult to detect in radio pulsar data, because they can leave no trace in polarized fractions and they are described by equation similar to the rotating vector model. The circularization, which coincides with flux minima at lower frequency, requires that profile components are formed by radiation with an oscillation phase that increases with longitude in steps of 90○ per component. The properties can be understood as an interference pattern involving two pairs of linear orthogonal modes (or two non-orthogonal elliptic waves). The frequency-dependent coherent superposition of coplanar oscillations can produce the minima in the pulse profile, and thereby the illusion of components as separate entities. The orthogonally polarized signal that is left after such negative interference explains the enhancement of polarization degree that is commonly observed in the minima between profile components.

scholarly journals Radio pulsar polarization as a coherent sum of orthogonal proper mode waves

2019 ◽  
Vol 488 (2) ◽  
pp. 2018-2040 ◽  
Author(s):  
J Dyks
Keyword(s):  
Amplitude Ratio ◽  
Radio Pulsar ◽  
Vector Model ◽  
Natural Mode ◽  
Propagation Mode ◽  
Orthogonal Polarization ◽  
Polarization Angle ◽  
Phase Lag ◽  
Complex Behaviour ◽  
Mode Amplitude

ABSTRACT Radio pulsar polarization exhibits a number of complex phenomena that are classified into the realm of ‘beyond the rotating vector model’ (RVM). It is shown that these effects can be understood in geometrical terms, as a result of coherent and quasi-coherent addition of elliptically polarized natural mode waves. The coherent summation implies that the observed tracks of polarization angle (PA) do not always correspond to the natural propagation mode (NPM) waves. Instead, they are statistical average of coherent sum of the NPM waves, and can be observed at any (and frequency-dependent) distance from the natural modes. Therefore, the observed tracks of PA can wander arbitrarily far from the RVM, and may be non-orthogonal. For equal amplitudes of the NPM waves two pairs of orthogonal polarization modes (OPMs), displaced by 45°, can be observed, depending on the width of lag distribution. Observed pulsar polarization mainly results from two independent effects: the change of mode amplitude ratio and the change of phase lag. In the core region both effects are superposed on each other, which can produce so complex behaviour as observed in the cores of PSR B1933+16, B1237+25, and J0437−4715. Change of the phase lag with frequency ν is mostly responsible for the observed strong evolution of these features with ν. The coherent addition of orthogonal natural waves is a useful interpretive tool for the observed radio pulsar polarization.

scholarly journals Artefacts of circumpolar cartography in radio pulsar polarization

2020 ◽  
Vol 495 (1) ◽  
pp. L118-L122 ◽  
Author(s):  
J Dyks
Keyword(s):  
Polarization State ◽  
Single Pulse ◽  
Vertical Axis ◽  
Radio Pulsar ◽  
Orthogonal Polarization ◽  
Polarization Angle ◽  
Polarization Effects ◽  
Poincaré Sphere ◽  
Power Content ◽  
Poincare Sphere

ABSTRACT Single-pulse data on radio pulsar polarization are traditionally presented in the form of two-dimensional grey-scale patterns with the pulse longitude and polarization angle (PA) on the horizontal and vertical axis, respectively. Such diagrams reveal several enigmatic polarization effects: (1) bifurcations and loops of PA curve under central pulse components, (2) vertical spread of flux at all PA values, (3) exchange of power content between PA tracks of two orthogonal polarization modes (OPMs), and (4) peripherically flat PA swings that span more than 180 deg. It is shown that all these phenomena result from passage of observed polarization state near the pure-V pole of Poincaré sphere. Much of their complexity results from cartographic transformation from Poincaré sphere to the longitude–PA plane. An odd number of near-pole passages produce apparent replacement of OPM power in the profile wings, although the same amount of flux keeps staying in each modal patch on the Poincaré sphere. The fitting of pulsar PA curves should therefore allow for transitions between the primary (strong) and secondary (weak) PA tracks. The Stokes space (or Poincaré sphere) representation of pulsar polarization data contains crucial polarization information and needs to accompany the traditional viewing if the published figures are to be fully useful for interpretation.

scholarly journals Coherent origin of peculiar polarization in radio pulsars

2017 ◽  
Vol 13 (S337) ◽  
pp. 332-333
Author(s):  
Jarosław Dyks
Keyword(s):  
Vector Model ◽  
Orthogonal Polarization ◽  
Polarization Angle ◽  
Radio Pulsars ◽  
Comparable Amount ◽  
Circular Polarisation ◽  
Polarized Emission ◽  
Core Components

AbstractThe observed polarization of radio pulsars involves several peculiar effects, such as comparable amount of orthogonal polarization modes (OPMs) which often bear the same handedness of circular polarisation V. In the average profiles of B1913+16 and B1933+16, orthogonal jumps of polarization angle (PA) are observed to occur at the maximum V, instead of V = 0. High levels of V are also observed in core components (eg. in B1237+25), where they are accompanied by strong distortions of PA from the rotating vector model. In weakly polarized emission, PA jumps by 45° are observed in B1919+21 and B0823+26. It is shown that all these peculiarities can be interpreted in a model which assumes coherent addition of waves in natural propagation modes.

scholarly journals Warped disks during type II outbursts in Be/X-ray binaries: evidence from optical polarimetry

2018 ◽  
Vol 619 ◽  
pp. A19 ◽  
Author(s):  
P. Reig ◽  
D. Blinov
Keyword(s):  
Neutron Star ◽  
Structural Changes ◽  
Degree Of Polarization ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Similar Amount ◽  
Type Ii ◽  
Line Profiles ◽  
X Ray ◽  
X Ray Binaries

Context. Current models that explain giant (type II) X-ray outbursts in Be/X-ray binaries (BeXB), are based on the idea of highly distorted disks. They are believed to occur when a misaligned and warped disk becomes eccentric, allowing the neutron star to capture a large amount of material. The BeXB 4U 0115+63 underwent two major outbursts in 2015 and 2017. Aims. Our aim is to investigate whether the structural changes in the disk expected during type II outbursts can be detected through optical polarimetry. Methods. We present the first optical polarimetric observations and new optical spectra of the BeXB 4U 0115+63 covering the period 2013–2017. We study in detail the shape of the Hα line profile and the polarization parameters before, during, and after the occurrence of a type II X-ray outburst. Results. We find significant changes in polarization degree and polarization angle and highly distorted line profiles during the 2017 X-ray outburst. The degree of polarization decreased by ∼1%, while the polarization angle, which is supposed to be related with the disk orientation, first increased by ∼10° in about two months and then decreased by a similar amount and on a similar timescale once the X-ray activity ceased. Conclusions. We interpret the polarimetric and spectroscopic variability as evidence for the presence of a warped disk.

Orthogonal Polarization in Pulsar Radio Emission

1975 ◽  
Vol 2 (6) ◽  
pp. 334-336 ◽  
Author(s):  
R.N. Manchester
Keyword(s):  
Source Region ◽  
Position Angle ◽  
Orthogonal Polarization ◽  
Magnetic Pole ◽  
Pulse Profile ◽  
Pulsar Radio ◽  
Emission Process ◽  
Integrated Or ◽  
Pulsar Radio Emission ◽  
Different Parts

For many pulsars the integrated or mean pulse profile is highly polarized. Generally linear polarization dominates over circular and there is a continuous variation of position angle through the profile (e.g. Manchester 1971). In most models for the emission process the angle of polarization is related to the (projected) direction of magnetic fields in the source region. Several of the observed properties of pulsars, for example, the mode-changing phenomenon (Backer 1970) and the different spectral index of different components of the intergrated profile (Manchester 1971), suggest that different parts of the integrated profile are emitted in different (though closely related) parts of the source. The different observed position angles across the integrated profile would then result from different projected magnetic field directions in these different parts of the source. For many pulsars the observed position angle variations are closely represented by a path through a radial set of projected field directions such as would be obtained in the vicinity of a magnetic pole (cf. Radhakrishnan and Cooke 1969).

scholarly journals POLARIZATION SWINGS FROM CURVED TRAJECTORIES OF THE EMITTING REGIONS

2010 ◽  
Vol 19 (06) ◽  
pp. 701-706 ◽  
Author(s):  
KRZYSZTOF NALEWAJKO
Keyword(s):  
Rotation Rate ◽  
Velocity Vector ◽  
Total Flux ◽  
Polarization Degree ◽  
Line Of Sight ◽  
Polarization Angle ◽  
Axially Symmetric ◽  
Curved Trajectories ◽  
The Moment

We present a model of polarization swings in blazars from axially symmetric blobs propagating on curved trajectories. If the minimum inclination of the velocity vector to the line of sight is smaller than Γ-1, the polarization angle maximum rotation rate is simultaneous with the polarization degree minimum and a spike in the total flux. By measuring the maximum rotation rate and the moment of the polarization maximum, it is possible to estimate the distance covered by the blob and thus its approximate position. We apply this model to the recent polarization event in blazar 3C 279.

scholarly journals Multiband optical flux density and polarization microvariability study of optically bright blazars

2019 ◽  
Vol 492 (1) ◽  
pp. 1295-1317 ◽  
Author(s):  
Magdalena Pasierb ◽  
Arti Goyal ◽  
Michał Ostrowski ◽  
Łukasz Stawarz ◽  
Paul J Wiita ◽  
...  
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Intermediate Frequency ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Spectral Indices ◽  
Spectral Evolution ◽  
Data Set ◽  
Internal Shock ◽  
Optical Flux

ABSTRACT We present the results of flux density, spectral index, and polarization intra-night monitoring studies of a sample of eight optically bright blazars, carried out by employing several small to moderate aperture (0.4 to 1.5 m diameter) telescopes fitted with CCDs and polarimeters located in Europe, India, and Japan. The duty cycle of flux variability for the targets is found to be ∼45 per cent, similar to that reported in earlier studies. The computed two-point spectral indices are found to be between 0.65 to 1.87 for our sample, comprised of low- and intermediate-frequency peaked blazars, with one exception: they are also found to be statistically variable for about half the instances where ‘confirmed’ variability is detected in flux density. In the analysis of the spectral evolution of the targets on hourly time-scale, a counterclockwise loop (soft-lagging) is noted in the flux–spectral index plane on two occasions, and in one case a clear spectral flattening with the decreasing flux is observed. In our data set, we also observe a variety of flux–polarization degree variability patterns, including instances with a relatively straightforward anticorrelation, correlation, or counterclockwise looping. These changes are typically reflected in the flux–polarization angle plane: the anticorrelation between the flux and polarization degree is accompanied by an anticorrelation between the polarization angle and flux, while the counterclockwise flux–PD looping behaviour is accompanied by a clockwise looping in the flux–polarization angle representation. We discuss our findings in the framework of the internal shock scenario for blazar sources.

3mm POLARIZATION PROPERTIES OF OPTICAL AND γ-RAY CLASSES OF BLAZARS

2010 ◽  
Vol 19 (06) ◽  
pp. 923-929
Author(s):  
I. AGUDO ◽  
C. THUM ◽  
H. WIESEMEYER ◽  
T. P. KRICHBAUM
Keyword(s):  
Linear Polarization ◽  
Position Angle ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Marginal Effect ◽  
Bl Lacertae ◽  
All Optical ◽  
Linearly Polarized ◽  
Γ Ray ◽  
The One

We have performed the first 3.5 mm polarimetric survey of radio loud active galactic nuclei (AGN) with the IRAM 30 m Telescope. Unlike radio wavelengths, millimeter observations allow us to measure the intrinsic linearly polarized emission from AGN, thanks to the marginal effect of Faraday rotation and depolarization at mm wavelengths. The sample contains 145 sources, and it essentially consists of all flat-spectrum AGN with declinations accessible to the 30 m Telescope (Dec. ( J 2000.0) > -30°), and with 3 mm flux density ≳ 1 Jy, as measured from 1978 to 1994. LBAS quasars in our sample show larger luminosity than non-LBAS ones, which is consistent with previous work claiming larger Doppler factors for brighter γ-ray blazars. This effect cannot be claimed for BL Lacertae objects in our sample, which suggests that only quasars contribute to distribute LBAS blazars towards larger luminosities. We find a systematic 3.5 mm linear polarization degree excess by a factor of ~ 2 with regard to the one at 2 cm for all optical and γ-ray classes of sources considered here. Our sample shows a significant trend to increase the luminosity of their jets for decreasing linear polarization fraction. Unlike previous studies in the radio spectral range, we do not find a clear relation between the linear polarization angle and the jet structural position angle of any source class in our sample. This is interpreted as a markedly non-axisymmetric character of the 3 mm emitting region of radio loud AGN jets.

scholarly journals The X-ray evolution and geometry of the 2018 outburst of XTE J1810–197

2021 ◽  
Author(s):  
A Borghese ◽  
N Rea ◽  
R Turolla ◽  
M Rigoselli ◽  
J A J Alford ◽  
...  
Keyword(s):  
Phase Shift ◽  
Radio Pulsar ◽  
Spectral Evolution ◽  
Pulse Profile ◽  
X Ray ◽  
Monitoring Campaign ◽  
Surface Emission ◽  
Energy Dependent ◽  
Star Surface

Abstract After 15 years, in late 2018, the magnetar XTE J1810–197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of two change in its spin-down rate from ∼7.2 × 10−12 s s−1 to ∼1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810–197 is well-modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810–197 has likely evolved relative to that found for the 2003 event.

scholarly journals Prospects for IXPE and eXTP polarimetric archaeology of the reflection nebulae in the Galactic center

2020 ◽  
Vol 643 ◽  
pp. A52
Author(s):  
L. Di Gesu ◽  
R. Ferrazzoli ◽  
I. Donnarumma ◽  
P. Soffitta ◽  
E. Costa ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Galactic Center ◽  
Region Of Interest ◽  
Polarization Degree ◽  
Polarization Angle ◽  
Diffuse Emission ◽  
X Ray ◽  
X Ray Imaging ◽  
Spread Function ◽  
Reflection Nebulae

The X-ray polarization properties of the reflection nebulae in the Galactic center inform us about the direction of the illuminating source (through the polarization angle) and the cloud position along the line of sight (through the polarization degree). However, the detected polarization degree is expected to be lowered because the polarized emission of the clouds is mixed with the unpolarized diffuse emission that permeates the Galactic center region. In a real observation, also the morphological smearing of the source due to the point spread function and the unpolarized instrumental background contribute in diluting the polarization degree. So far, these effects have never been included in the estimation of the dilution. We evaluate the detectability of the X-ray polarization predicted for the MC2, Bridge-B2, G0.11-0.11, Sgr B2, Sgr C1, Sgr C2, and Sgr C3 molecular clouds with modern X-ray imaging polarimeters such as the Imaging X-ray Polarimetry Explorer (IXPE), which is expected to launch in 2021, and the Enhanced X-ray Timing and Polarimetry mission (eXTP), whose launch is scheduled for 2027. We perform realistic simulations of X-ray polarimetric observations considering (with the aid of Chandra maps and spectra) the spatial, spectral, and polarization properties of all the diffuse emission and background components in each region of interest. We find that in the 4.0–8.0 keV band, where the emission of the molecular clouds outshines the other components, the dilution of the polarization degree, including the contribution due to the morphological smearing of the source, ranges between ~19% and ~55%. We conclude that for some distance values reported in the literature, the diluted polarization degree of G0.11-0.11, Sgr B2, Bridge-B2, Bridge-E, Sgr C1, and Sgr C3 may be detectable in a 2 Ms long IXPE observations. With the same exposure time, and considering the whole range of possible distances reported in the literature, the enhanced capabilities of eXTP may allow detecting the 4.0–8.0 keV of all the targets considered here.

Sign in / Sign up

Export Citation Format

Share Document