Polarimetric imaging of large fields in radio astronomy

Sault, R. J.; Bock, Douglas C.-J.; Duncan, A. R.

doi:10.1051/aas:1999400

Cited by 49 publications

(48 citation statements)

References 10 publications

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“…We then applied a maximum entropy algorithm (Gull & Daniell 1978) to deconvolve all of the dirty maps. For 20 and 13 cm, the task MAXEN was employed; for 6 and 3 cm, we used the task PMOSMEM (Sault et al 1999) to deconvolve the Stokes I, Q, and U maps simultaneously. After that, we convolved the resultant models with synthesized beams of FWHM 26″×19″ for 20 cm, 16″×11″ for 13 cm, 15″×13″ for 6 cm, and 10″×8″ for 3 cm.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Radio Polarization Observations of the Snail: A Crushed Pulsar Wind Nebula in G327.1–1.1 With a Highly Ordered Magnetic Field

Bucciantini

et al. 2016

ApJ

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Pulsar wind nebulae (PWNe) are suggested to be acceleration sites of cosmic rays in the Galaxy. While the magnetic field plays an important role in the acceleration process, previous observations of magnetic field configurations of PWNe are rare, particularly for evolved systems. We present a radio polarization study of the "Snail" PWN inside the supernova remnant G327.1−1.1 using the Australia Telescope Compact Array. This PWN is believed to have been recently crushed by the supernova (SN) reverse shock. The radio morphology is composed of a main circular body with a finger-like protrusion. We detected a strong linear polarization signal from the emission, which reflects a highly ordered magnetic field in the PWN and is in contrast to the turbulent environment with a tangled magnetic field generally expected from hydrodynamical simulations. This could suggest that the characteristic turbulence scale is larger than the radio beam size. We built a toy model to explore this possibility, and found that a simulated PWN with a turbulence scale of about one-eighth to one-sixth of the nebula radius and a pulsar wind filling factor of 50%-75% provides the best match to observations. This implies substantial mixing between the SN ejecta and pulsar wind material in this system.

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Section: Observations and Data Reductionmentioning

confidence: 99%

Radio Polarization Observations of the Snail: A Crushed Pulsar Wind Nebula in G327.1–1.1 With a Highly Ordered Magnetic Field

Bucciantini

et al. 2016

ApJ

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“…At 20 and 13 cm these images were deconvolved using the CLEAN algorithm, while at 6 cm we used the PMOSMEM algorithm (Sault, Bock, & Duncan 1999). Q and U images in each waveband were then combined to form images of polarized intensity and polarized position angle; a correction for the Ricean bias was applied to these data.…”

Section: Observations and Analysismentioning

confidence: 99%

A Multifrequency Radio Study of Supernova Remnant G292.0+1.8 and Its Pulsar Wind Nebula

Gaensler

Wallace²

2003

ApJ

121

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We present a detailed radio study of the young supernova remnant (SNR) G292.0+1.8 and its associated pulsar PSR J1124À5916, using the Australia Telescope Compact Array at observing wavelengths of 20, 13, and 6 cm. We find that the radio morphology of the source consists of three main components: a polarized flat-spectrum central core coincident with the pulsar J1124À5916, a surrounding circular steep-spectrum plateau with sharp outer edges, and superposed on the plateau, a series of radial filaments with spectra significantly flatter than their surroundings. H i absorption argues for a lower limit on the distance to the system of 6 kpc. The core clearly corresponds to radio emission from a pulsar wind nebula powered by PSR J1124À5916, while we conclude that the plateau represents the surrounding SNR shell. The plateau's sharp outer rim delineates the SNR's forward shock, while the thickness of the plateau region demonstrates that the forward and reverse shocks are well separated. Assuming a distance of 6 kpc and an age for the source of 2500 yr, we infer an expansion velocity for the SNR of $1200 km s À1 , an ambient density $0.9 cm À3 , an ejected mass $5.9 M , and a supernova explosion energy $1:1 Â 10 51 ergs. We interpret the flat-spectrum radial filaments superposed on the steeper spectrum plateau as Rayleigh-Taylor unstable regions between the forward and reverse shocks of the SNR. The flat radio spectrum seen for these features results from efficient second-order Fermi acceleration in strongly amplified magnetic fields.

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“…MEM imaging algorithms have been in use for decades (e.g., Gull &Daniell 1978 andCornwell &Evans 1985), but because of early computational limitations, they are used infrequently compared to CLEAN. The theory behind polarimetric MEM was pioneered in several theoretical papers beginning in the 70s (Ponsonby 1973;Nityananda & Narayan 1983;Narayan & Nityananda 1986;Shevgaonkar 1987), but implementation on actual VLBI data has been limited to only a handful of studies since (Holdaway 1990;Holdaway & Wardle 1990;Sault et al 1999;Coughlan & Gabuzda 2012, 2013.…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Linear Polarimetric Imaging for the Event Horizon Telescope

Chael

Johnson

Narayan

et al. 2016

ApJ

231

318

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Images of the linear polarizations of synchrotron radiation around active galactic nuclei (AGNs) highlight their projected magnetic field lines and provide key data for understanding the physics of accretion and outflow from supermassive black holes. The highest-resolution polarimetric images of AGNs are produced with Very Long Baseline Interferometry (VLBI). Because VLBI incompletely samples the Fourier transform of the source image, any image reconstruction that fills in unmeasured spatial frequencies will not be unique and reconstruction algorithms are required. In this paper, we explore some extensions of the Maximum Entropy Method (MEM) to linear polarimetric VLBI imaging. In contrast to previous work, our polarimetric MEM algorithm combines a Stokes I imager that only uses bispectrum measurements that are immune to atmospheric phase corruption, with a joint Stokes Q and U imager that operates on robust polarimetric ratios. We demonstrate the effectiveness of our technique on 7 and 3 mm wavelength quasar observations from the VLBA and simulated 1.3 mm Event Horizon Telescope observations of Sgr A * and M87. Consistent with past studies, we find that polarimetric MEM can produce superior resolution compared to the standard CLEAN algorithm, when imaging smooth and compact source distributions. As an imaging framework, MEM is highly adaptable, allowing a range of constraints on polarization structure. Polarimetric MEM is thus an attractive choice for image reconstruction with the EHT.

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Polarimetric imaging of large fields in radio astronomy

Cited by 49 publications

References 10 publications

Radio Polarization Observations of the Snail: A Crushed Pulsar Wind Nebula in G327.1–1.1 With a Highly Ordered Magnetic Field

Radio Polarization Observations of the Snail: A Crushed Pulsar Wind Nebula in G327.1–1.1 With a Highly Ordered Magnetic Field

A Multifrequency Radio Study of Supernova Remnant G292.0+1.8 and Its Pulsar Wind Nebula

High-Resolution Linear Polarimetric Imaging for the Event Horizon Telescope

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