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
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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
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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)
