The Murchison Widefield Array: Design Overview

Lonsdale, Colin J.; Cappallo, R. J.; Morales, M. F.; Briggs, F.; Benkevitch, L. V.; Bowman, Judd D.; Bunton, John D.; Burns, S.; Corey, B. E.; deSouza, L.; Doeleman, Sheperd S.; Derome, M.; Deshpande, A. A.; Gopala, M.R.; Greenhill, L. J.; Herne, D.; Hewitt, Jacqueline N.; Kamini, P. A.; Kasper, J. C.; Kincaid, B. B.; Kocz, J.; Kowald, E.; Kratzenberg, E.; Kumar, Deepak; Lynch, M. J.; Srinivasan, Madhavi; Matejek, Michael; Mitchell, D. A.; Morgan, E.; Oberoi, D.; Ord, S. M.; Pathikulangara, J.; Prabu, T.; Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Sault, R. J.; Shankar, N. Udaya; Srivani, K. S.; Stevens, J.; Tingay, S. J.; Vaccarella, Annino; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, Anne; Williams, Christopher

doi:10.1109/jproc.2009.2017564

Cited by 359 publications

(270 citation statements)

References 16 publications

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“…The collecting area for the UTR-2 (Abranin et al 2001) is quoted for a frequency of 20 MHz and the 5-beam and 8-beam modes are discussed in Ryabov et al (2010) and Abranin et al (2001) respectively. The Murchison Widefield Array (MWA) can have 32 single polarisation beams and the area is quoted for a frequency of 200 MHz (Lonsdale et al 2009). LOFAR can have up to a total of 244 station beams which equals the number of subbands.…”

Section: Lofarmentioning

confidence: 99%

Observing pulsars and fast transients with LOFAR

Stappers

Hessels

Alexov

et al. 2011

A&A

215

160

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Low frequency radio waves, while challenging to observe, are a rich source of information about pulsars. The LOw Frequency ARray (LOFAR) is a new radio interferometer operating in the lowest 4 octaves of the ionospheric "radio window": 10-240 MHz, that will greatly facilitate observing pulsars at low radio frequencies. Through the huge collecting area, long baselines, and flexible digital hardware, it is expected that LOFAR will revolutionize radio astronomy at the lowest frequencies visible from Earth. LOFAR is a next-generation radio telescope and a pathfinder to the Square Kilometre Array (SKA), in that it incorporates advanced multi-beaming techniques between thousands of individual elements. We discuss the motivation for low-frequency pulsar observations in general and the potential of LOFAR in addressing these science goals. We present LOFAR as it is designed to perform high-time-resolution observations of pulsars and other fast transients, and outline the various relevant observing modes and data reduction pipelines that are already or will soon be implemented to facilitate these observations. A number of results obtained from commissioning observations are presented to demonstrate the exciting potential of the telescope. This paper outlines the case for low frequency pulsar observations and is also intended to serve as a reference for upcoming pulsar/fast transient science papers with LOFAR.

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Section: Lofarmentioning

confidence: 99%

Observing pulsars and fast transients with LOFAR

Stappers

Hessels

Alexov

et al. 2011

A&A

215

160

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“…4.2. Detection of the reionization at 21 cm has been an active field in the last decade, and different groups have built instruments to detect a reionization signal around 100 MHz: LOFAR (Rottering et al 2006), MWA (Bowman et al 2007;Lonsdale et al 2009), and PAPER (Parsons et al 2010). Several authors have studied the instrumental noise and statistical uncertainties when measuring the reionization signal power spectrum, and the methods presented here to compute the instrument response and sensitivities are similar to the ones developed in these publications (Morales & Hewitt 2004;Bowman et al 2006;McQuinn et al 2006).…”

Section: Instrument Responsementioning

confidence: 99%

21 cm observation of large-scale structures atz ~ 1

Ansari

Campagne

Colom

et al. 2012

A&A

101

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Context. Large-scale structures (LSS) in the universe can be traced using the neutral atomic hydrogen H I through its 21 cm emission. Such a 3D matter distribution map can be used to test the cosmological model and to constrain the dark energy properties or its equation of state. A novel approach, called intensity mapping, can be used to map the H I distribution, using radio interferometers with a large instantaneous field of view and waveband. Aims. We study the sensitivity of different radio interferometer configurations, or multi-beam instruments for observing LSS and baryon acoustic oscillations (BAO) in 21 cm, and we discuss the problem of foreground removal. Methods. For each configuration, we determined instrument response by computing the (u, v) or Fourier angular frequency plane coverage using visibilities. The (u, v) plane response determines the noise power spectrum, hence the instrument sensitivity for LSS P(k) measurement. We also describe a simple foreground subtraction method of separating LSS 21 cm signal from the foreground due to the galactic synchrotron and radio source emission. Results. We have computed the noise power spectrum for different instrument configurations, as well as the extracted LSS power spectrum, after separating the 21 cm-LSS signal from the foregrounds. We have also obtained the uncertainties on the dark energy parameters for an optimized 21 cm BAO survey. Conclusions. We show that a radio instrument with few hundred simultaneous beams and a collecting area of ∼10 000 m 2 will be able to detect BAO signal at redshift z ∼ 1 and will be competitive with optical surveys.

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“…Studies of polarisation at frequencies below 300 MHz are now becoming possible, partly due to the construction of LOFAR (van Haarlem et al 2013) and the Murchison Widefield Array (MWA; Lonsdale et al 2009), and to the introduction of new techniques to analyse polarisation, in particular RM synthesis (Brentjens & de Bruyn 2005). Recently, Bernardi et al (2013) performed a 2400 square degree polarisation survey at 189 MHz with the MWA with a 7 beam.…”

Section: Introductionmentioning

confidence: 99%

The nature of the low-frequency emission of M 51

Mulcahy

Horneffer²,

Beck³

et al. 2014

A&A

113

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Context. Low-frequency radio continuum observations (<300 MHz) can provide valuable information on the propagation of low-energy cosmic ray electrons (CRE). Nearby spiral galaxies have hardly been studied in this frequency range because of the technical challenges of low-frequency radio interferometry. This is now changing with the start of operations of LOFAR. Aims. We aim to study the propagation of low-energy CRE in the interarm regions and the extended disk of the nearly face-on spiral galaxy Messier 51. We also search for polarisation in M 51 and other extragalactic sources in the field. Methods. The grand-design spiral galaxy M 51 was observed with the LOFAR High Frequency Antennas (HBA) and imaged in total intensity and polarisation. This observation covered the frequencies between 115 MHz and 175 MHz with 244 subbands of 8 channels each, resulting in 1952 channels. This allowed us to use RM synthesis to search for polarisation. Results. We produced an image of total emission of M 51 at the mean frequency of 151 MHz with 20 resolution and 0.3 mJy rms noise, which is the most sensitive image of a galaxy at frequencies below 300 MHz so far. The integrated spectrum of total radio emission is described well by a power law, while flat spectral indices in the central region indicate thermal absorption. We observe that the disk extends out to 16 kpc and see a break in the radial profile near the optical radius of the disk. The radial scale lengths in the inner and outer disks are greater at 151 MHz, and the break is smoother at 151 MHz than those observed at 1.4 GHz. The arm-interarm contrast is lower at 151 MHz than at 1400 MHz, indicating propagation of CRE from spiral arms into interarm regions. The correlations between the images of radio emission at 151 MHz and 1400 MHz and the FIR emission at 70 μm reveal breaks on scales of 1.4 and 0.7 kpc, respectively. The total (equipartition) magnetic field strength decreases from about 28 μG in the central region to about 10 μG at 10 kpc radius. No significant polarisation was detected from M 51, owing to severe Faraday depolarisation. Six extragalactic sources are detected in polarisation in the M 51 field of 4.1 • × 4.1 • size. Two sources show complex structures in Faraday space. Conclusions. Our main results, the scale lengths of the inner and outer disks at 151 MHz and 1.4 GHz, arm-interarm contrast, and the break scales of the radio-FIR correlations, can be explained consistently by CRE diffusion, leading to a longer propagation length of CRE of lower energy. The distribution of CRE sources drops sharply at about 10 kpc radius, where the star formation rate also decreases sharply. We find evidence that thermal absorption is primarily caused by H ii regions. The non-detection of polarisation from M 51 at 151 MHz is consistent with the estimates of Faraday depolarisation. Future searches for polarised emission in this frequency range should concentrate on regions with low star formation rates.Key words. polarization -cosmic rays -galaxies: ISM -galaxies: ...

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The Murchison Widefield Array: Design Overview

Abstract: Abstract-

Cited by 359 publications

References 16 publications

Observing pulsars and fast transients with LOFAR

Observing pulsars and fast transients with LOFAR

21 cm observation of large-scale structures atz ~ 1

The nature of the low-frequency emission of M 51

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