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Jul 03, 2023 47 likes •387 views

Compact sources at low frequencies using interplanetary scintillation with the Murchison Widefield Array J-P Macquart (Curtin) John Morgan (Curtin) Rajan Chhetri (Curtin) Ron Ekers (CASS) John Surveys and Angular Resolutions Credit: Heald et

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Compact sources at low frequencies using interplanetary scintillation with the Murchison Widefield Array

J-P Macquart (Curtin) John Morgan (Curtin) Rajan Chhetri (Curtin) Ron Ekers (CASS)

John
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Surveys and Angular Resolutions

Credit: Heald et al. 2015

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Surveys and Angular Resolutions

Credit: Heald et al. 2015

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The Instrument

› The Murchison Widefield Array (Western Australia) › 128 tiles with 2 x 16 dipoles each › Operating frequencies: 80 – 300 MHz › Bandwidth: 30.72 MHz

Credit: NRAO/AUI (modified) Credit: N. Hurley-Walker

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The Enabling Instrument

› The Murchison Widefield Array (Western Australia) › 128 tiles with 2 x 16 dipoles each › Operating frequencies: 80 – 300 MHz › Bandwidth: 30.72 MHz › Field of View: 15 – 50 degrees (200 – 2500 sq degrees) › Temporal resolution: 0.5 sec › Excellent instantaneous UV coverage

Credit: NRAO/AUI (modified) Credit: N. Hurley-Walker

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Typical MWA field

Angular resolution ~ 2'

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MWA field in TGSS

Angular resolution ~ 25''

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Current Low Frequency Instruments' challenge

Image credit: N. Hurley-Walker

› Field of View: 15 – 50 degrees (200 – 2500 sq degrees) › Very large number of sources in the field of view › Angular resolution (3-km array) at 150 MHz > 2 arcmin

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The Low Frequency solution?

› Field of View: 15 – 50 degrees (200 – 2500 sq degrees) › Very large number of sources in the field of view › Angular resolution (3-km array) at 150 MHz > 2 arcmin

Image credit: EXPRes website

VLBI

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The Low Frequency solution?

› Field of View: 15 – 50 degrees (200 – 2500 sq degrees) › Very large number of sources in the field of view › Angular resolution (3-km array) at 150 MHz > 2 arcmin › Time consuming › Very high number of sources Not a practical solution

Image credit: EXPRes website

VLBI

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Interplanetary Scintillation

Compact radio sources (< 1 arcsec) + Turbulence in interplanetary plasma = Scintillation effects (random fluctuations in flux density)

Credit: Readhead+1978

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Interplanetary Scintillation

Compact radio sources (< 1 arcsec) + Turbulence in interplanetary plasma = Scintillation effects (random fluctuations in flux density) Analogous to the effects of twinkling of stars in optical wavelengths

Credit: Readhead+1978

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Interplanetary Scintillation

Field started by: M. Clarke Hewish, Scott & Wills Nature 1964 Survey of the Northern sky by Purvis et al. 1987 Dedicated instruments e.g. STELab (Japan)

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Background on IPS with MWA

  • Pilot study by J. Morgan, Curtin University
  • Regular daytime observations (late December 2015 – July 2016)
  • Observations at two bands 80 MHz & 160 MHz
  • Over 4000 observations made of different parts of sky
  • Highest (0.5 second) temporal resolution of the MWA correlator
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IPS strategy with MWA

Simulated MWA beam at 150 MHz

Credit: Tingay et al. 2012

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How do we do it?

  • Image data as a continuum image
  • Image at 0.5 second integration in both frequency bands and polarisations
  • Produce variance image across ~ 600 images
  • Run source finding script – Aegean (Hancock et al. 2012)

Data processing

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Variance Imaging

  • Image data as a continuum image
  • Image at 0.5 second integration in both frequency bands and polarisations
  • Produce variance image across ~ 600 images
  • Run source finding script – Aegean (Hancock et al. 2012)
  • Identify sub arcsecond compact components in large number of

MWA sources simultaneously

Data processing

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Typical MWA field

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Typical MWA field

Field size: 23 x 8 sq degrees

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Using Variance Imaging

Field size: 23 x 8 sq degrees

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Scintillating Source

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Non Scintillating Source

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Some Results

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Some Results

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Some Results

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Some Results

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Detect Numerous Peaked-Spectrum Sources

SEDs Credit: Joe Callingham

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Higher moment images

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Surveys and Angular Resolutions

Credit: Heald et al. 2015

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Surveys and Angular Resolutions

Credit: Heald et al. 2015

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Summary

  • Extremely efficient identification of compact sources at arcsecond scales

at low radio frequencies from wide-field images.

  • Estimates of active cores: a very small fraction (~5%) as opposed to >80%

at high radio frequency (20 GHz).

  • Angular size estimates for peaked sources that are readily identified.
  • Excellent complement to GLEAM and TGSS.
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Thank you

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Some Results

IPS affected by ionospheric effects?

RA Dec

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The visibility-spectra plot