Parametrizing Epoch of Reionization foregrounds: a deep survey of low-frequency point-source spectra with the Murchison Widefield Array

Offringa, A. R.; Trott, Cathryn M.; Hurley‐Walker, N.; Johnston‐Hollitt, M.; McKinley, B.; Barry, N.; Beardsley, Adam P.; Bowman, Judd D.; Briggs, F.; Carroll, P.; Dillon, Joshua S.; Ewall‐Wice, Aaron; Lü, Feng; Gaensler, B. M.; Greenhill, L. J.; Hazelton, B. J.; Hewitt, Jacqueline N.; Jacobs, Daniel; Kim, H.-S.; Kittiwisit, Piyanat; Lenc, E.; Line, J.; Loeb, Abraham; Mitchell, D. A.; Morales, M. F.; Neben, Abraham R.; Paul, S.; Pindor, B.; Pober, Jonathan C.; Procopio, P.; Riding, J.; Sethi, Shiv K.; Shankar, N. Udaya; Subrahmanyan, R.; Sullivan, M.; Tegmark, Max; Thyagarajan, Nithyanandan; Tingay, S. J.; Wayth, R. B.; Webster, R. L.; Wyithe, J. Stuart B.

doi:10.1093/mnras/stw310

Cited by 75 publications

(94 citation statements)

References 71 publications

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“…This would be consistent with the 22% circular polarization observed in the integrated pulse profile of the pulsar at 648 MHz (McCulloch et al 1978). Offringa et al (2016) performed a deep point-source survey of the EoR-0 field using 45 hr of MWA data and achieved a sensitivity of 0.6 mJy beam −1 in polarization. Using a novel peeling algorithm, spectra for the 586 brightest sources in the field were presented.…”

supporting

confidence: 73%

“…PKS J0021-1910 appears in the catalog but is not detected in polarization. The Offringa et al (2016) survey did not consider Faraday rotation of the source and so linearly polarized sources with non-zero RM are depolarized. In addition, when combining results from multiple epochs, ionospheric Faraday rotation was also not considered; this too would lead to depolarization of linearly polarized sources (a similar issue was encountered by Moore et al 2016 in PAPER observations).…”

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confidence: 99%

“…In addition, when combining results from multiple epochs, ionospheric Faraday rotation was also not considered; this too would lead to depolarization of linearly polarized sources (a similar issue was encountered by Moore et al 2016 in PAPER observations). It is thus not surprising that linearly polarized sources were not detected by Offringa et al (2016), but circularly polarized sources should not be as greatly affected when combining data from multiple epochs. …”

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confidence: 99%

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Low-Frequency Observations of Linearly Polarized Structures in the Interstellar Medium Near the South Galactic Pole

Lenc

Gaensler

Sun

et al. 2016

ApJ

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We present deep polarimetric observations at 154 MHz with the Murchison Widefield Array (MWA), covering 625 deg 2 centered on α=0 h andδ=−27°. The sensitivity available in our deep observations allows an in-band, frequency-dependent analysis of polarized structure for the first time at long wavelengths. Our analysis suggests that the polarized structures are dominated by intrinsic emission but may also have a foreground Faraday screen component. At these wavelengths, the compactness of the MWA baseline distribution provides excellent snapshot sensitivity to large-scale structure. The observations are sensitive to diffuse polarized emission at ∼54′ resolution with a sensitivity of 5.9 mJy beam −1 and compact polarized sources at ∼2 4 resolution with a sensitivity of 2.3 mJy beam −1 for a subset (400 deg 2 ) of this field. The sensitivity allows the effect of ionospheric Faraday rotation to be spatially and temporally measured directly from the diffuse polarized background. Our observations reveal large-scale structures (∼1°-8°in extent) in linear polarization clearly detectable in ∼2 minute snapshots, which would remain undetectable by interferometers with minimum baseline lengths of >110 m at 154 MHz. The brightness temperature of these structures is on average 4 K in polarized intensity, peaking at 11 K. Rotation measure synthesis reveals that the structures have Faraday depths ranging from −2 to 10 rad m −2 with a large fraction peaking at approximately+1 rad m −2 . We estimate a distance of 51±20 pc to the polarized emission based on measurements of the in-field pulsar J2330-2005. We detect four extragalactic linearly polarized point sources within the field in our compact source survey. Based on the known polarized source population at 1.4 GHz and non-detections at 154 MHz, we estimate an upper limit on the depolarization ratio of 0.08 from 1.4 GHz to 154 MHz.

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confidence: 73%

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confidence: 99%

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confidence: 99%

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Low-Frequency Observations of Linearly Polarized Structures in the Interstellar Medium Near the South Galactic Pole

Lenc

Gaensler

Sun

et al. 2016

ApJ

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“…The calibration and imaging process of the EoR0 data is presented and discussed in detail in Offringa et al (2016).…”

Section: Mwa Epoch Of Reionization (Eor) Datamentioning

confidence: 99%

Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

Kapińska

Staveley‐Smith

Crocker

et al. 2017

ApJ

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We present new radio continuum observations of NGC253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of a central starburst and extended emission. The central component, corresponding to the inner 500 pc of the starburst region of the galaxy, is best modeled as an internally free-free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the spectrum of NGC253 is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the southeast halo, and may be indicative of synchrotron self-absorption of shock-reaccelerated electrons or an intrinsic low-energy cutoff of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC253 in our radio images. At 154-231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ∼8 kpc in the z-direction (from the major axis).

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“…Central to most analysis strategies is the concept of an "EoR window"-the region of Fourier space where spectrally smooth foregrounds have been isolated from the isotropic (spherically symmetric in Fourier space) cosmological signal Bowman et al 2009). More recent studies have shown the existence of a foreground "wedge," the result of instrumental mode mixing, throwing power from spectrally smooth foregrounds to higher Fourier modes (Datta et al 2010;Morales et al 2012;Trott et al 2012;Vedantham et al 2012;Hazelton et al 2013;Pober et al 2013;Thyagarajan et al 2013Thyagarajan et al , 2015aThyagarajan et al , 2015bLiu et al 2014aLiu et al , 2014b, while others are investigating the spectral structure of point sources themselves (e.g., Offringa et al 2016). The EoR window is still expected to be preserved above the wedge, and several analysis pipelines are under active development to exploit this foreground isolation (e.g., Dillon et al 2013Dillon et al , 2015bTrott 2014; B. J.…”

Section: Introductionmentioning

confidence: 99%

First Season Mwa Eor Power Spectrum Results at Redshift 7

Beardsley

Hazelton

Sullivan

et al. 2016

ApJ

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The Murchison Widefield Array (MWA) has collected hundreds of hours of Epoch of Reionization (EoR) data and now faces the challenge of overcoming foreground and systematic contamination to reduce the data to a cosmological measurement. We introduce several novel analysis techniques, such as cable reflection calibration, hyper-resolution gridding kernels, diffuse foreground model subtraction, and quality control methods. Each change to the analysis pipeline is tested against a two-dimensional power spectrum figure of merit to demonstrate improvement. We incorporate the new techniques into a deep integration of 32 hoursof MWA data. This data set is used to place a systematic-limited upper limit on the cosmological power spectrum of  D2.7 10 2 4 mK 2 at k = 0.27 h Mpc −1 and z = 7.1, consistent with other published limits, and a modest improvement (factor of 1.4) over previous MWA results. From this deep analysis, we have identified a list of improvements to be made to our EoR data analysis strategies. These improvements will be implemented in the future and detailed in upcoming publications.

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Parametrizing Epoch of Reionization foregrounds: a deep survey of low-frequency point-source spectra with the Murchison Widefield Array

Cited by 75 publications

References 71 publications

Low-Frequency Observations of Linearly Polarized Structures in the Interstellar Medium Near the South Galactic Pole

Low-Frequency Observations of Linearly Polarized Structures in the Interstellar Medium Near the South Galactic Pole

Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

First Season Mwa Eor Power Spectrum Results at Redshift 7

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