Ramesh BhatSwinburne University of Technology(on behalf of the MWA collaboration)The Murchison Wide Field Array (MWA)

@ Murchison, ~300 km from Geraldton

The PartnershipMIT Haystack Observatory (Project Office)MIT Kavli InstituteHarvard Smithsonian Center for AstrophysicsUMelbourne, Curtin Uni, Aus Nat UniUSydney, UTasmania, Uni Western AusATNF CSIRO (via synergy with ASKAP)Raman Research Institute, India

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MWA Science GoalsEpoch of ReionizationPower spectrumStrmgren spheresSolar/Heliospheric/Ionospheric Science (SHI)Solar imagingFaraday rotation B field of CMEs and heliosphereInterplanetary ScintillationSmall scale ionospheric structureTransientsDeep blind surveyLight curves (field and targeted)Synoptic surveysOtherGalactic and Extra-galactic astronomyPulsarsISM surveyRecombination lines...

Epoch of Reionisation (EOR)After ~300,000 years electrons and protons combine to form hydrogen

After ~1 billion years stars and quasars ignite, radiation splits hydrogen into protons and electrons.

In between are the Dark Ages

Solar and Heliospheric science

MWA Science GoalsEpoch of ReionizationPower spectrumStrmgren spheresSolar/Heliospheric/Ionospheric Science (SHI)Solar imagingFaraday rotation B field of CMEs and heliosphereInterplanetary ScintillationSmall scale ionospheric structureTransientsDeep blind surveyLight curves (field and targeted)Synoptic surveysOtherGalactic and Extra-galactic astronomyPulsarsISM surveyRecombination lines...

Murchison Widefield Array: Design*

Murchison Widefield Array: Specs

Frequency range80-300 MHzNumber of receptors8192 dual polarization dipolesNumber of tiles512Collecting area~8000 m2 (at 200 MHz)Field of View~15-50 (1000 deg2 at 200 MHz)ConfigurationCore array ~1.5 km diameter (95%, 3.4) +extended array ~3 km diameter (5%, 1.7)Bandwidth220 MHz (Sampled); 31 MHz (Processed)# Spectral channels1024Temporal resolution8 secPolarizationFull StokesPoint source sensitivity20mJy in 1 sec (32 MHz, 200 MHz)0.34mJy in 1 hrMulti-beam capability32, single polarizationNumber of baselines130,816 (VLA: 351, GMRT: 435, ATA: 861 )

1.5 kmArray Configuration

Data Flow Diagram

RFI Environment

Early Deployment: 3 Tile System

Galaxy (single tile)

Solar (Type 3) Burst

Crab giant pulse detections with the ED systemBhat, Wayth, Knight, et al. (2007), ApJ, 665, 618System:3 tiles - G ~ 0.01 K/JyTsys ~ 200 + 180 KBW ~ 0.75 x 8 MHz Freq = 200 MHz# GPs ( > 9 kJy) = 31

Giant pulse and (fast) transient detection prospects with MWABhat et al. (2008)

32 Tile PrototypeMotivation Engineering test bedEnd to end signal/data path and system performance testingTraining data sets for calibration systemLearning to operate in the site conditionsEarly Science

32 Tile system: Specs

32 tiles, 4 nodest = 50 ms Aeff = 550 m2 (~6% of MWA)0 ~15 @ 200 MHzBandwidth = 31 MHz496 physical baselines = 10 kHzMax data rate ~12.7 Mvis/s (1TByte in ~2h45min)

6 Tile system6 tiles from the 32 availableFirst field testing of the prototype receiverBandwidth 1.28 MHzOffline software correlation Essentially arbitrary spectral and time resolution Extremely well suited for imaging of solar bursts

Early 6T resultsuv coverage

Some Images

Real time system for calibration and imaging: signal processing challenges Data volume - 19 GB/sRaw visibility cannot be storedDedicated hardware for correlation and data processingLarge FOV Wide FOV requires new approach to integrating, imaging (and deconvolution)Gain and polarisation responses are direction dependentCalibrationMust be real time, since visibilities are not storedIonosphere shifts source positions by ~arcminutesIonosphere should be a phase ramp over arrayIonospheric faraday rotation

The MWA Real Time System (RTS)

Calibration and measurement loop

MWA RTS - The Imaging pipeline Mitchell, Greenhill, Wayth, et al. (2008), IEEE

Real time system: Computational costsParameters (8 second cadence):40 peel sources, 400 iono sources1125^2 image size (primary beam)768 frequency channels, 130000 visibilitiesCalibration:3.3 TflopGrid and image:1.8 TflopStokes conv:4.3 TflopRegridding:? (0.05 to 28 Tflops)Approx total:10 Tflop (efficient regrid) (over 8 seconds)

User access to the MWA Not an open facility - as originally proposedSome partners have proposed a user facilityCurrent policy - Interested pulsar users are welcome to join the collaboration Pulsar science - part of the transient science collaboration - coordinators: Roger Cappallo (MIT) and Shami Chatterjee (Univ. Syd)Current (pulsar) members: Bhat, Bailes, Deshpande

Concluding Remarks MWA - a major low frequency instrument in the southern hemisphereStatus: 32T system by Q4 2008, full system by 2009Primary science: EOR, transients, solarA great instrument for pulsars (G ~ 3 K/Jy)Early pulsar science - Crab giants @200 MHzInterested users are welcome to join the collaboration (transients + pulsars)

***The partners who have a signed MoU*The list of Science Objective, I have not added any details about the SHI stuff, I thought that it will be difficult to included those in a 15 min talk. If you think it would be useful to include them, please feel free***The list of Science Objective, I have not added any details about the SHI stuff, I thought that it will be difficult to included those in a 15 min talk. If you think it would be useful to include them, please feel freeThis should give people a good idea of the overall structure of the array. It basically builds up the array from the dipoles to the tiles to the nodes and the entire array. Though the array design here does not show it, the array will include 16 tiles outside the 1.5 km dia circle. The primary motivation for these tiles is to increase the resolution of the array to make it more useful for solar imaging. It might be worth mentioning it to this audience. BTW, to give you a feel for the background picture, the breakaway you see is almost aligned NS and is ~260m in length. The MWA site is due East of the breakaway and the region being considered for core is probably a little outside the edge of the image.**A summary of useful design specs, I have marked the ones you might want to highlightArray configuration - The array is shown at three different scales, and overlaid onto an aerial photograph of the local terrain. Tiles are shown to scale in red or purple (for the existing 32T tiles), shallow trenches for coax cable from tiles to nodes is shown in blue, deep trenches for AC and fibre are depicted in black with the central deep trenches (with conduits) in green. The 7 cyan circles in a hexagonal pattern represent breakout points in the inner dense part of the array, around which multiple nodes are clustered. The yellow lines are a contour plot with half meter intervals.

***Early deployment system (2005) consisted off 3 tiles*****The background picture shows the 32 tiles deployed on the site.*The Aperture plane shows the actual layout of tiles on the site and the uv plane shows the equivalent mirror corresponding to a snap-shot, mono-chromatic observation of the zenith. I have included a similar figure for the data which we have, to allow people to get a feel for the performance of the 32 T system vs the 6 T system for which the data is being presented.

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