Ramesh BhatRamesh BhatSwinburne University of TechnologySwinburne University of Technology(on behalf of the MWA collaboration)(on behalf of the MWA collaboration)

The Murchison Wide Field Array (MWA)

@ Murchison, ~300 km from Geraldton

The Partnership

MIT Haystack Observatory (Project Office) MIT Kavli Institute Harvard Smithsonian Center for Astrophysics UMelbourne, Curtin Uni, Aus Nat Uni USydney, UTasmania, Uni Western Aus ATNF CSIRO (via synergy with ASKAP) Raman Research Institute, India

3

MWA Science Goals Epoch of Reionization

Power spectrum Strömgren spheres

Solar/Heliospheric/Ionospheric Science (SHI) Solar imaging Faraday rotation – B field of CME’s and heliosphere Interplanetary Scintillation Small scale ionospheric structure

Transients Deep blind survey Light curves (field and targeted) Synoptic surveys …

Other Galactic and Extra-galactic astronomy Pulsars ISM survey Recombination 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 Goals Epoch of Reionization

Power spectrum Strömgren spheres

Solar/Heliospheric/Ionospheric Science (SHI) Solar imaging Faraday rotation – B field of CME’s and heliosphere Interplanetary Scintillation Small scale ionospheric structure

Transients Deep blind survey Light curves (field and targeted) Synoptic surveys …

Other Galactic and Extra-galactic astronomy Pulsars ISM survey Recombination lines ...

Murchison Widefield Array: Design

8

Murchison Widefield Array: SpecsFrequency rangeFrequency range 80-300 MHz80-300 MHz

Number of receptorsNumber of receptors 8192 dual polarization dipoles8192 dual polarization dipoles

Number of tilesNumber of tiles 512512

Collecting areaCollecting area ~8000 m~8000 m2 2 (at 200 MHz)(at 200 MHz)

Field of ViewField of View ~15°-50° (1000 deg~15°-50° (1000 deg22 at 200 MHz) at 200 MHz)

ConfigurationConfiguration Core array ~1.5 km diameter Core array ~1.5 km diameter (95%, 3.4’) +(95%, 3.4’) +

extended array ~3 km diameter extended array ~3 km diameter (5%, 1.7’)(5%, 1.7’)

BandwidthBandwidth 220 MHz (Sampled); 31 MHz 220 MHz (Sampled); 31 MHz (Processed)(Processed)

# Spectral channels# Spectral channels 10241024

Temporal resolutionTemporal resolution 8 sec8 sec

PolarizationPolarization Full StokesFull Stokes

Point source Point source sensitivitysensitivity

20mJy in 1 sec (32 MHz, 200 MHz)20mJy in 1 sec (32 MHz, 200 MHz)

0.34mJy in 1 hr0.34mJy in 1 hr

Multi-beam Multi-beam capabilitycapability

32, single polarization32, single polarization

Number of baselinesNumber of baselines 130,816 (VLA: 351, GMRT: 435, 130,816 (VLA: 351, GMRT: 435, ATA: 861 )ATA: 861 )

1.5 km

Array Configuration

500 m

1.5 km

120 m

Data Flow Diagram

RFI Environment

Early Deployment: 3 Tile System

Galaxy (single tile)

Solar (Type 3) Burst

Crab giant pulse detections with the ED system

Bhat, Wayth, Knight, et al. (2007), ApJ, 665, 618

System:

3 tiles - G ~ 0.01 K/Jy

Tsys ~ 200 + 180 K

BW ~ 0.75 x 8 MHz

Freq = 200 MHz

# GPs ( > 9 kJy) = 31

Giant pulse and (fast) transient detection prospects with MWA

Bhat et al. (2008)

32 Tile Prototype

Motivation 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

Aperture plane uv plane

32 tiles, 4 nodes ∆t = 50 ms

Aeff = 550 m2 (~6% of MWA) 0 ~15’ @ 200 MHz

Bandwidth = 31 MHz 496 physical baselines

∆ = 10 kHz Max data rate ~12.7 Mvis/s (1TByte in ~2h45min)

6 Tile system

6 tiles from the 32 available First field testing of the prototype

receiver Bandwidth – 1.28 MHz Offline software correlation Essentially

arbitrary spectral and time resolution – Extremely well suited for imaging of solar bursts

Early 6T results

uv coverage

Closure Phase

Ph

ase

(d

eg

)

Time (4 hrs)

Amplitude band shapes

1.28 MHz

Phase band shapes

Some Images

Real time system for calibration and imaging: signal processing challenges

Data volume - 19 GB/s Raw visibility cannot be stored Dedicated hardware for correlation and data processing

Large FOV Wide FOV requires new approach to integrating, imaging (and

deconvolution) Gain and polarisation responses are direction dependent

Calibration Must be real time, since visibilities are not stored Ionosphere shifts source positions by ~arcminutes Ionosphere should be a phase ramp over array Ionospheric 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 costs Parameters (8 second cadence):

40 peel sources, 400 iono sources1125^2 image size (primary beam)768 frequency channels, 130000 visibilities

Calibration: 3.3 Tflop Grid and image:1.8 Tflop Stokes conv: 4.3 Tflop Regridding: ? (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 proposed Some partners have proposed a “user facility” Current 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 hemisphere Status: 32T system by Q4 2008, full system by

2009 Primary science: EOR, transients, solar A great instrument for pulsars (G ~ 3 K/Jy) Early pulsar science - Crab giants @200 MHz Interested users are welcome to join the

collaboration (transients + pulsars)