scholarly journals Analytic detection thresholds for measurements of linearly polarized intensity using rotation measure synthesis

2012 ◽  
Vol 424 (3) ◽  
pp. 2160-2172 ◽  
Author(s):  
C. A. Hales ◽  
B. M. Gaensler ◽  
R. P. Norris ◽  
E. Middelberg
Keyword(s):  
Detection Thresholds ◽  
Rotation Measure ◽  
Linearly Polarized

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 Decomposing the internal faraday rotation of black hole accretion flows

2020 ◽  
Vol 498 (4) ◽  
pp. 5468-5488
Author(s):  
Angelo Ricarte ◽  
Ben S Prather ◽  
George N Wong ◽  
Ramesh Narayan ◽  
Charles Gammie ◽  
...  
Keyword(s):  
Event Horizon ◽  
Faraday Rotation ◽  
Polarization Plane ◽  
Time Variability ◽  
Accretion Flows ◽  
Spatially Resolved ◽  
Rotation Measure ◽  
Linearly Polarized ◽  
General Relativistic ◽  
Sgr A

ABSTRACT Faraday rotation has been seen at millimeter wavelengths in several low-luminosity active galactic nuclei, including Event Horizon Telescope (EHT) targets M87* and Sgr A*. The observed rotation measure (RM) probes the density, magnetic field, and temperature of material integrated along the line of sight. To better understand how accretion disc conditions are reflected in the RM, we perform polarized radiative transfer calculations using a set of general relativistic magnetohydrodynamic (GRMHD) simulations appropriate for M87*. We find that in spatially resolved millimetre wavelength images on event horizon scales, the RM can vary by orders of magnitude and even flip sign. The observational consequences of this spatial structure include significant time-variability, sign-flips, and non-λ2 evolution of the polarization plane. For some models, we find that internal RM can cause significant bandwidth depolarization even across the relatively narrow fractional bandwidths observed by the EHT. We decompose the linearly polarized emission in these models based on their RM and find that emission in front of the mid-plane can exhibit orders of magnitude less Faraday rotation than emission originating from behind the mid-plane or within the photon ring. We confirm that the spatially unresolved (i.e. image integrated) RM is a poor predictor of the accretion rate, with substantial scatter stemming from time variability and inclination effects. Models can be constrained with repeated observations to characterize time variability and the degree of non-λ2 evolution of the polarization plane.

scholarly journals Long-term variability of a black widow’s eclipses – A decade of PSR J2051$-$0827

2019 ◽  
Vol 490 (1) ◽  
pp. 889-908 ◽  
Author(s):  
E J Polzin ◽  
R P Breton ◽  
B W Stappers ◽  
B Bhattacharyya ◽  
G H Janssen ◽  
...  
Keyword(s):  
Time Scales ◽  
Orbital Period ◽  
Mass Loss Rate ◽  
Low Frequency ◽  
Line Of Sight ◽  
Cyclotron Absorption ◽  
Rotation Measure ◽  
Linearly Polarized ◽  
Model Fits

ABSTRACT In this paper we report on $\sim 10$  yr of observations of PSR J2051$-$0827, at radio frequencies in the range 110–4032 MHz. We investigate the eclipse phenomena of this black widow pulsar using model fits of increased dispersion and scattering of the pulsed radio emission as it traverses the eclipse medium. These model fits reveal variability in dispersion features on time-scales as short as the orbital period, and previously unknown trends on time-scales of months–years. No clear patterns are found between the low-frequency eclipse widths, orbital period variations, and trends in the intrabinary material density. Using polarization calibrated observations we present the first available limits on the strength of magnetic fields within the eclipse region of this system; the average line of sight field is constrained to be $10^{-4}$ G $\lesssim B_{||} \lesssim 10^2$ G, while for the case of a field directed near-perpendicular to the line of sight we find $B_{\perp } \lesssim 0.3$ G. Depolarization of the linearly polarized pulses during the eclipse is detected and attributed to rapid rotation measure fluctuations of $\sigma _{\text{RM}} \gtrsim 100$ rad m$^{-2}$ along, or across, the line of sights averaged over during a subintegration. The results are considered in the context of eclipse mechanisms, and we find scattering and/or cyclotron absorption provide the most promising explanation, while dispersion smearing is conclusively ruled out. Finally, we estimate the mass-loss rate from the companion to be $\dot{M}_{\text{C}} \sim 10^{-12}\, \mathrm{M}_\odot$ yr$^{-1}$, suggesting that the companion will not be fully evaporated on any reasonable time-scale

scholarly journals Detection Thresholds and Bias Correction in Polarized Intensity

2012 ◽  
Vol 29 (3) ◽  
pp. 214-220 ◽  
Author(s):  
Samuel J. George ◽  
Jeroen M. Stil ◽  
Ben W. Keller
Keyword(s):  
Gaussian Noise ◽  
Bias Correction ◽  
Detection Rate ◽  
Detection Threshold ◽  
False Detection Rate ◽  
False Detection ◽  
Detection Thresholds ◽  
Detection Rates ◽  
Rotation Measure ◽  
Non Gaussian

AbstractDetection thresholds in polarized intensity and polarization bias correction are investigated for surveys where the polarization information is obtained from rotation measure (RM) synthesis. Considering unresolved sources with a single RM, a detection threshold of 8 σQU applied to the Faraday spectrum will retrieve the RM with a false detection rate less than 10−4, but polarized intensity is more strongly biased than Ricean statistics suggest. For a detection threshold of 5 σQU, the false detection rate increases to ∼4%, depending also on λ2 coverage and the extent of the Faraday spectrum. Non-Gaussian noise in Stokes Q and U due to imperfect imaging and calibration can be represented by a distribution that is the sum of a Gaussian and an exponential. The non-Gaussian wings of the noise distribution increase the false detection rate in polarized intensity by orders of magnitude. Monte Carlo simulations assuming non-Gaussian noise in Q and U give false detection rates at 8 σQU similar to Ricean false detection rates at 4.9 σQU.

scholarly journals Polarization study of the pulsars in the globular cluster 47 Tucanae

2017 ◽  
Vol 13 (S337) ◽  
pp. 295-298
Author(s):  
F. Abbate ◽  
A. Possenti ◽  
C. Tiburzi ◽  
W. van Straten ◽  
E. Barr ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Globular Cluster ◽  
Galactic Disk ◽  
Line Of Sight ◽  
Radio Telescopes ◽  
Parallel Component ◽  
Polarization Study ◽  
Rotation Measure ◽  
Linearly Polarized ◽  
The Magnetic Field

AbstractThe linearly polarized component of a pulsar signal at different radio frequencies can help to constrain the parallel component of the magnetic field along the line of sight. In this work we measured the polarimetric properties of the pulsars in the globular cluster 47 Tucanae and we report the Rotation Measure (RM) for 13 of them. A gradient in the RM values of the pulsars across the cluster is detected suggesting the presence of significant variations in the magnetic field across the very small angular scales associated with the lines of sight to the pulsars in 47 Tucanae. Both magnetic fields located in the globular cluster or in the Galactic disk in the direction of the cluster are taken into consideration. However, more detailed modelling of the dynamics of the cluster and deeper observations with the MeerKAT and/or the SKA1 radio telescopes are necessary to discriminate among the models.

scholarly journals Strategy to Explore Magnetized Cosmic Web with Forthcoming Large Surveys of Rotation Measure

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 118 ◽  
Author(s):  
Takuya Akahori
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Line Of Sight ◽  
Wide Field ◽  
Sky Surveys ◽  
Rotation Measure ◽  
Polarized Emission ◽  
Linearly Polarized ◽  
Intergalactic Magnetic Field ◽  
The Universe

The warm-hot intergalactic medium (WHIM) is a candidate for the missing baryons in the Universe. If the WHIM is permeated with the intergalactic magnetic field (IGMF), the Faraday rotation measure (RM) of the WHIM is imprinted in linearly-polarized emission from extragalactic objects. In this article, we discuss strategies to explore the WHIM’s RM from forthcoming radio broadband and wide-field polarization sky surveys. There will be two observational breakthroughs in the coming decades; the RM grid and Faraday tomography. They will allow us to find ideal RM sources for the study of the IGMF and give us unique information of the WHIM along the line of sight.

scholarly journals Magnetic field at a jet base: extreme Faraday rotation in 3C 273 revealed by ALMA

2019 ◽  
Vol 623 ◽  
pp. A111 ◽  
Author(s):  
T. Hovatta ◽  
S. O’Sullivan ◽  
I. Martí-Vidal ◽  
T. Savolainen ◽  
A. Tchekhovskoy
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Position Angle ◽  
High Angular Resolution ◽  
Systematic Uncertainties ◽  
Rotation Measure ◽  
Linearly Polarized ◽  
Polarization Fraction ◽  
The Magnetic Field ◽  
Quasar 3C 273

Aims. We studied the polarization behavior of the quasar 3C 273 over the 1 mm wavelength band at ALMA with a total bandwidth of 7.5 GHz across 223–243 GHz at 0.8′′ resolution, corresponding to 2.1 kpc at the distance of 3C 273. With these observations we were able to probe the optically thin polarized emission close to the jet base, and constrain the magnetic field structure. Methods. We computed the Faraday rotation measure using simple linear fitting and Faraday rotation measure synthesis. In addition, we modeled the broadband behavior of the fractional Stokes Q and U parameters (qu-fitting). The systematic uncertainties in the polarization observations at ALMA were assessed through Monte Carlo simulations. Results. We find the unresolved core of 3C 273 to be 1.8% linearly polarized. We detect a very high rotation measure (RM) of (5.0 ± 0.3) × 105 rad m−2 over the 1 mm band when assuming a single polarized component and an external RM screen. This results in a rotation of >40° of the intrinsic electric vector position angle, which is significantly higher than typically assumed for millimeter wavelengths. The polarization fraction increases as a function of wavelength, which according to our qu-fitting could be due to multiple polarized components of different Faraday depth within our beam or to internal Faraday rotation. With our limited wavelength coverage we cannot distinguish between the cases, and additional multifrequency and high angular resolution observations are needed to determine the location and structure of the magnetic field of the Faraday active region. Comparing our RM estimate with values obtained at lower frequencies, the RM increases as a function of observing frequency, following a power law with an index of 2.0 ± 0.2, consistent with a sheath surrounding a conically expanding jet. We also detect ~0.2% circular polarization, although further observations are needed to confirm this result.

Analysis and Identification of Off-Odor Compounds in Electronic Systems

2006 ◽  
Author(s):  
Mary Ann Nailos ◽  
Dan Stein ◽  
Lawrence T. Nielsen ◽  
Anna Iwasinska
Keyword(s):  
Volatile Compounds ◽  
Electronic Systems ◽  
Detection Thresholds ◽  
Detection And Identification ◽  
Odor Compounds ◽  
Novel Method ◽  
Odor Analysis ◽  
Analytical System ◽  
Task Perception ◽  
Analytical Tools

Abstract The detection and identification of substances that give rise to aromas and off-odors is often a difficult task. Perception of odors is very subjective and odor detection thresholds vary from person to person. The identification of trace levels of compounds responsible for perceived odors is difficult using conventional analytical tools. This paper will focus on a novel method for sampling and analyzing aromatic volatile compounds using an analytical system specifically designed for odor analysis.

Olfactometric characterisation of sludge odours

2000 ◽  
Vol 41 (6) ◽  
pp. 49-55 ◽  
Author(s):  
S. D. Lambert ◽  
A. L. Beaman ◽  
P. Winter
Keyword(s):  
Recent Work ◽  
Sewage Treatment ◽  
Limited Information ◽  
Hedonic Tone ◽  
Detection Thresholds ◽  
Remediation Measures ◽  
Odour Concentration ◽  
Odour Profile ◽  
Storage Facilities

Conventional olfactometric techniques have been used to evaluate odours from sewage treatment and sludge storage facilities primarily in terms of odour concentration relative to their detection thresholds. However, such data conveys limited information that would be useful for determining the causes of most odours or the most appropriate remediation measures to be taken. Thispaper discusses some recent work undertaken to characterise the olfactometric profiles of different odours. Standard descriptive terms were used to characterise odours at normalised, moderately strong concentrations. These were used directly for the calculation of hedonic tone. They were also collated into a small number of generic odour groups and plotted to allow visual comparisons of different odour profile fingerprints. Such odour characterisations have proved to be very useful and may easily be incorporated into normal olfactometric evaluations.

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