scholarly journals The dynamic magnetosphere of Swift J1818.0−1607

2020 ◽  
Author(s):  
M E Lower ◽  
S Johnston ◽  
R M Shannon ◽  
M Bailes ◽  
F Camilo
Keyword(s):  
Radio Emission ◽  
Radio Pulse ◽  
Position Angle ◽  
Wide Frequency Range ◽  
Ultra Wideband ◽  
Mode Switching ◽  
Rotation Axes ◽  
Linearly Polarized ◽  
Emission Mode ◽  
Field Lines

Abstract Radio-loud magnetars display a wide variety of radio-pulse phenomenology seldom seen among the population of rotation-powered pulsars. Spectropolarimetry of the radio pulses from these objects has the potential to place constraints on their magnetic topology and unveil clues about the magnetar radio emission mechanism. Here we report on eight observations of the magnetar Swift J1818.0−1607 taken with the Parkes Ultra-Wideband Low receiver covering a wide frequency range from 0.7 to 4 GHz over a period of 5 months. The magnetar exhibits significant temporal profile evolution over this period, including the emergence of a new profile component with an inverted spectrum, two distinct types of radio emission mode switching, detected during two separate observations, and the appearance and disappearance of multiple polarization modes. These various phenomena are likely a result of ongoing reconfiguration of the plasma content and electric currents within the magnetosphere. Geometric fits to the linearly polarized position angle indicate we are viewing the magnetar at an angle of ∼99○ from the spin axis, and its magnetic and rotation axes are misaligned by ∼112○. While conducting these fits, we found the position angle swing had reversed direction on MJD 59062 compared to observations taken 15 days earlier and 12 days later. We speculate this phenomena may be evidence the radio emission from this magnetar originates from magnetic field lines associated with two co-located magnetic poles that are connected by a coronal loop.

scholarly journals Physics of radio emission in gamma-ray pulsars

2016 ◽  
Vol 82 (2) ◽  
Author(s):  
S. A. Petrova
Keyword(s):  
Radio Emission ◽  
Gamma Ray ◽  
Radio Pulse ◽  
Position Angle ◽  
Resonant Absorption ◽  
Main Pulse ◽  
Wide Sense ◽  
Density Profiles ◽  
Millisecond Pulsars ◽  
Open Field Line

Propagation of radio emission in a pulsar magnetosphere is reviewed. The effects of polarization transfer, induced scattering and reprocessing to high energies are analysed with a special emphasis on the implications for the gamma-ray pulsars. The possibilities of the pulsar plasma diagnostics based on the observed radio pulse characteristics are also outlined. As an example, the plasma number density profiles obtained from the polarization data for the Vela and the gamma-ray millisecond pulsars J1446-4701, J1939+2134 and J1744-1134 are presented. The number densities derived tend to be the highest/lowest when the radio pulse leads/lags the gamma-ray peak. In the PSR J1939+2134, the plasma density profiles for the main pulse and interpulse appear to fit exactly the same curve, testifying to the origin of both radio components above the same magnetic pole and their propagation through the same plasma flow in opposite directions. The millisecond radio pulse components exhibiting flat position angle curves are suggested to result from the induced scattering of the main pulse by the same particles that generate gamma rays. This is believed to underlie the wide-sense radio/gamma-ray correlation in the millisecond pulsars. The radio quietness of young gamma-ray pulsars is attributed to resonant absorption, whereas the radio loudness to the radio beam escape through the periphery of the open field line tube.

scholarly journals Modeling of Pulsar Polarization Properties

1992 ◽  
Vol 128 ◽  
pp. 378-383
Author(s):  
L. M. Shier ◽  
F. C. Michel
Keyword(s):  
Position Angle ◽  
Orthogonal Polarization ◽  
Magnetic Pole ◽  
Hollow Cone ◽  
Pulsar Emission ◽  
Average Polarization ◽  
Cone Model ◽  
Curvature Radiation ◽  
Linearly Polarized ◽  
Field Lines

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.

scholarly journals Evolution and Radiation in Pulsar Polar Cap Models

1981 ◽  
Vol 95 ◽  
pp. 87-98 ◽  
Author(s):  
M. Ruderman
Keyword(s):  
Mode Switching ◽  
Orthogonal Polarization ◽  
Polar Cap ◽  
Mature Adult ◽  
Inverse Compton Scattering ◽  
Polar Caps ◽  
Double Beam ◽  
Linearly Polarized ◽  
Field Lines ◽  
Fe Ions

Positively charged particle emission from pulsar polar caps evolves through many stages as the cap temperature cools. In “infant” pulsars, stripped Fe ions interact with secondary e± from a 1012 V discharge maintained just above the cap to give coherent radio emission at very high frequencies in a very broad beam. In “adolescent” pulsars such as the Crab and Vela, lower energy Fe ions interact with streams of protons produced in the surface by photonuclear reactions to give lower frequency highly linearly polarized radiation. There is no cap e± discharge. In mature “adult” pulsars proton and/or Fe ion streams from discharge heated patches on the polar cap interact with a relativistic e± plasma to give coherent radio subpulse beams which can drift, have strong submillisecond modulations, and orthogonal polarization mode switching. Young pulsars, and some older ones, can support additional more energetic e± discharges on some open field lines in the outer magnetosphere. These all give strong double beams of GeV γ-rays and weaker γ-ray beams above ~ 1012 eV. With Crab pulsar parameters an e± plasma associated with such a discharge also can give optical and X-ray double beams. If illuminated by the normal pulsar beam (precursor) coherent inverse Compton scattering also contributes a double beam of harder radio frequencies.

scholarly journals Periastron Observations of the PSR B1259-63/SS 2883 Binary System

1996 ◽  
Vol 165 ◽  
pp. 263-269
Author(s):  
Simon Johnston
Keyword(s):  
Galactic Plane ◽  
Radio Spectrum ◽  
Wide Frequency Range ◽  
Optical Observations ◽  
Rotation Measure ◽  
Linearly Polarized ◽  
Be Star ◽  
Frequency Survey ◽  
The Magnetic Field

PSR B1259-63 is a 47-millisecond pulsar which was discovered in a high frequency survey of the galactic plane (Johnston et al. 1992a) and was subsequently found to be in a highly eccentric orbit with a main-sequence Be star known as SS 2883 (Johnston et al. 1992b). Radio observations of the pulsar led to a phase connected timing solution which predicted the epoch of periastron to be 1994 January 9 (MJD 49361.2); optical observations of the Be star led to a determination of its mass and of the size of its circumstellar disk (Johnston et al. 1994a): the star is of approximate spectral type B1e, with mass 10 M⊙ and radius 6 R⊙. If this mass is correct and the pulsar has a mass of 1.4 M⊙, then the inclination angle of the plane of the orbit with respect to the sky is 35°. This pulsar has an unusually flat radio spectrum compared to most pulsars, which makes it easily detectable up to 8.4 GHz. The narrow pulse permits dispersion and scattering measurements for studying the ionized plasma in the system. Moreover, the pulses are highly linearly polarized and permit determination of the rotation measure (RM), allowing measurements of the magnetic field along the line of sight. The 3.5-yr orbit of the pulsar around its companion thus provides us with an excellent probe of the stellar wind of the Be star over a wide frequency range.

scholarly journals Compact Liquid Crystal Based Tunable Band-Stop Filter with an Ultra-Wide Stopband by Using Wave Interference Technique

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Longzhu Cai ◽  
Huan Xu ◽  
Daping Chu
Keyword(s):  
Liquid Crystal ◽  
Impedance Matching ◽  
Wide Frequency Range ◽  
Ultra Wideband ◽  
New Wave ◽  
Wave Interference ◽  
Rejection Level ◽  
Band Stop Filter ◽  
The Individual ◽  
Uwb Applications

A wave interference filtering section that consists of three stubs of different lengths, each with an individual stopband of its own central frequency, is reported here for the design of band-stop filters (BSFs) with ultra-wide and sharp stopbands as well as large attenuation characteristics. The superposition of the individual stopbands provides the coverage over an ultra-wide frequency range. Equations and guidelines are presented for the application of a new wave interference technique to adjust the rejection level and width of its stopband. Based on that, an electrically tunable ultra-wide stopband BSF using a liquid crystal (LC) material for ultra-wideband (UWB) applications is designed. Careful treatment of the bent stubs, including impedance matching of the main microstrip line and bent stubs together with that of the SMA connectors and impedance adaptors, was carried out for the compactness and minimum insertion and reflection losses. The experimental results of the fabricated device agree very well with that of the simulation. The centre rejection frequency as measured can be tuned between 4.434 and 4.814 GHz when a biased voltage of 0–20 Vrms is used. The 3 dB and 25 dB stopband bandwidths were 4.86 GHz and 2.51 GHz, respectively, which are larger than that of other recently reported LC based tunable BSFs.

Dispersion distortions of wide spectrum signals during their propagation in the Earth ionosphere

Antennas ◽  
2021 ◽  
Author(s):  
M. M. Ivoylova ◽  
A. V. Kashin ◽  
V. A. Kozlov
Keyword(s):  
Electromagnetic Compatibility ◽  
Wide Spectrum ◽  
Radio Pulse ◽  
Current Trend ◽  
Polarization Plane ◽  
Leading Edge ◽  
Ultrashort Pulses ◽  
Ultra Wideband ◽  
Engineering Systems ◽  
Middle Latitudes

The current trend in the development of radio engineering systems (RES) is to use wide spectrum signals, the application of which provides an increase in the resolution and secrecy of the radar operation, an increase in the speed and volume of transmitted information for communication and telemetry systems. The class of such signals includes ultrashort pulses (USP signals), radio pulses with linear frequency modulation (chirp signals). Also of interest are ultra-wideband (UWB) noise signals (UWBN signals), which have high electromagnetic compatibility, stealth and noise immunity. When designing promising ground-based and space-based RES using wide spectrum signals, an important task is to determine the distortions of their envelope shape and distortions of spectrum, as well as the change in the polarization of the emitted wave when passing through the Earth's ionosphere, since taking these distortions into account will provide conditions for optimal reception. This article presents the numerical assessment results of the expected distortions of the wide spectrum signals main types of the decimeter wavelength range, for middle latitudes at heights from 100 km to 1000 km. The conversion of the emitted pulse into a frequency modulated radio pulse is typical for the USP signal. For a chirp radio pulse with a monotonically increasing frequency, an initial decrease in duration with an increase in amplitude and subsequent stretching in time with further spread is typical (the amplitude change is estimated due to a change in the signal shape without taking into account spread). For a chirp radio pulse with a monotonically falling frequency and a UWBN signal, dispersion distortions manifest themselves as an increase in their duration with a decrease in amplitude. For all signal types under consideration that have passed through the ionosphere, a leading edge lag is observed, the dependences of frequency on time at an altitude of 1000 km are repeated and are close to hyperbolic character, the energy spectra envelope shape of the considered signals is almost not distorted. The polarization plane rotation for signals with a spectrum concentrated in the frequency range above 0.7 GHz does not exceed 45

scholarly journals A 1 to 32 GHz broadband multi-octave receiver for monolithic integrated vector network analyzers in SiGe technology

2018 ◽  
Vol 10 (5-6) ◽  
pp. 717-728
Author(s):  
Marco Dietz ◽  
Andreas Bauch ◽  
Klaus Aufinger ◽  
Robert Weigel ◽  
Amelie Hagelauer
Keyword(s):  
Noise Figure ◽  
Gain Control ◽  
Wide Frequency Range ◽  
Low Noise ◽  
Vector Network Analyzer ◽  
Ultra Wideband ◽  
Network Analyzer ◽  
Active Mixer ◽  
Input Matching ◽  
Better Than

AbstractA multi-octave receiver chain is presented for the use in a monolithic integrated vector network analyzer. The receiver exhibits a very wide frequency range of 1–32 GHz, where the gain meets the 3 dB-criterion. The differential receiver consists of an ultra-wideband low noise amplifier, an active mixer and an output buffer and exhibits a maximum conversion gain (CG) of 16.6 dB. The main design goal is a very flat CG over five octaves, which eases calibration of the monolithic integrated vector network analyzer. To realize variable gain functionality, without losing much input matching, an extended gain control circuit with additional feedback branch is shown. For the maximum gain level, a matching better than −10 dB is achieved between 1–28 GHz, and up to 30.5 GHz the matching is better than −8.4 dB. For both, the input matching and the gain of the LNA, the influence of the fabrication tolerances are investigated. A second gain control is implemented to improve isolation. The measured isolations between RF-to-LO and LO-to-RF are better than 30 dB and 60 dB, respectively. The LO-to-IF isolation is better than 35 dB. The noise figure of the broadband receiver is between 4.6 and 5.8 dB for 4–32 GHz and the output referred 1-dB-compression-point varies from 0.1 to 4.3 dBm from 2–32 GHz. The receiver draws a current of max. 66 mA at 3.3 V.

scholarly journals Characteristics of Pulsar Radio Emission at Single-pulse Resolution

2000 ◽  
Vol 177 ◽  
pp. 149-154
Author(s):  
Avinash A. Deshpande
Keyword(s):  
Radio Emission ◽  
Weighted Average ◽  
Single Pulse ◽  
Position Angle ◽  
Complex Nature ◽  
Stable States ◽  
Pulsar Radio ◽  
Emission Profile ◽  
Secondary State ◽  
Pulsar Radio Emission

Pulsar radio emission shows remarkably rich, but complex behavior in both intensity and polarization when considered on a pulse-to-pulse basis. A large number of pulses, when averaged together, tend to approach & define stable shapes that can be considered as distinct signatures of different pulsars. Such average profiles have shapes ranging from that describable as a simple one-component profile to those suggesting as many as 9 components. The components are understood as resulting from an average of many, often narrower, intities — the subpulses —that appear within the longitude range of a given component. The pulse components are thusformedand represent statistically an intensity-weighted average pattern of the radiation received as a function of longitude. The profile mode changes recognized in many pulsars suggest that the emission profile of a given pulsar may have two quasi-stable states, with one (primary) state more probable/brighter than the other (secondary) state. There are also (often associated) polarization modes that represent polarization states that are orthogonal to each other. The complex nature of orthogonaljumpsobserved in polarization position-angle sweeps may be attributable to possible superposition of two profile/polarization modes with orthogonal polarizations.

scholarly journals Study of the Magnetic Field of the Galaxy using Correlation Functions of the Intensity of Synchrotron Background Radio Emission

1996 ◽  
Vol 169 ◽  
pp. 615-616
Author(s):  
V.R. Shoutenkov
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Correlation Functions ◽  
Theoretical Calculations ◽  
Angular Separation ◽  
Field Studies ◽  
Position Angle ◽  
The Galaxy ◽  
Image Position ◽  
The Magnetic Field

The possibility to study magnetic field of the Galaxy calculating correlation or structure functions of synchrotron background radio emission have been known long ago (Kaplan and Pikel'ner (1963); Getmantsev (1958)). But this method had not been as popular as other methods of magnetic field studies. However theoretical calculations made by Chibisov and Ptuskin (1981) showed that correlation functions of intensity of synchrotron background radio emission can give a lot of valuable information about galactic magnetic fields because of the intensity of synchrotron background radio emission depends on H⊥. According to this theory correlation C(θ, φ) and structure S(θ, φ) functions of intensity, as functions of angular separation θ between two lines of sight and position angle φ on the sky between this two lines of sight, can be presented as a sum of isotropic (not dependent from angle φ) and anisotropic parts:

scholarly journals Dynamics of the superfine structure in the Orion KL jet

2002 ◽  
Vol 206 ◽  
pp. 96-99
Author(s):  
Leonid I. Matveyenko ◽  
Phil J. Diamond ◽  
David A. Graham
Keyword(s):  
Molecular Cloud ◽  
Angular Resolution ◽  
Position Angle ◽  
Maser Emission ◽  
Quiescent Period ◽  
Brightness Temperatures ◽  
Rotation Axes ◽  
Superfine Structure ◽  
High Level ◽  
Bright Source

We have studied the superfine structure of the active H2O maser region in Orion KL with an angular resolution of ≤ 0.3 × 0.7 mas. The high level of H2O maser emission from 1979-1988 was due to an accretion disk, which is divided into five groups of protoplanetary rings. The peak brightness temperatures of the structures was Tpeak = 1013-14 K. The region is located in the OMC-1 molecular cloud, VLSR ⋍ 7.74 km/s. The cloud amplifies by more than two orders of magnitude the emission from the structures, whose radial velocities are within the maser window ±0.3 km/s. Due to this, the velocity of the H2O super maser emission is constant. In the quiescent period of 1995 a 6 AU jet was discovered, PA = −32°, Tb ⋍ 1011K. In 1998 the jet's brightness temperature increased by more than 3 orders of magnitude. Initially the jet's position angle was PA = −45°, and then changed to PA = −38°. During the period of decreasing emission in 1999 the jet had changed its form and became a helix, that suggests the precession of the rotation axes. In the central part of the jet there is a compact bright source - “the ejector” - with Tejc = 1017 K.

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