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Multi-beaming & Wide Field Surveys

Anne Green University of Sydney

15 May, 2003

Multibeaming & Wide Field Surveys

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Outline ! ! ! ! Multibeaming definitions Molonglo Observatory Synthesis Telescope The SKAMP Project SKA & Multiple possibilities

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Multibeaming principles and definitions

! ! ! !

Everyone is doing it! Let's get the terms right Primary beam ­ individual element Fields of view & multiple beams

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Multi beams
Station beams
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Element antenna pattern = primary beam Synthesized beams from correlator

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8

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! Observing teams with their own beams
! Can have all beams simultaneously

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Molonglo Observatory Synthesis Telescope

Photo: G. Warr

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Current Observing Statistics
! ! ! ! ! ! ! ! 843 MHz continuum 3 MHz bandwidth 43" spatial resolution Field of view 23' ­ 160' Number of beams formed 128 - 896 Sensitivity ~1 mJy/beam Dynamic range ~200:1 Full synthesis in 12 hr
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V( ) = e
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n=- N

N

j

2



( nx ) sin( )

~

sin(L / ) (L / )

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Rotation of fan beams during an observation

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A wider field of view with minimum grating artefacts

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Instantaneous versus synthesis visibility functions & beamshapes

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Continuous uv coverage gives excellent image quality:

750 m

1.6 km

(Bock et al. 1999)

!Continuous uv coverage from 15 m to 1.6 km in 12hr synthesis
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Faxplot and image for Field 2144 (J0127-366)

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Faxplot and image for Field 971 (J2018-557)

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Real time beam-forming at Molonglo

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Coverage with small Field of View (1982 ­ 1997)

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SUMSS Survey Fields < -30 degrees (1997 ­ 2003)

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Molonglo Galactic Plane Survey
image at 843 MHz

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The Square Kilometre Array Molonglo Prototype (SKAMP) Goal: To equip the Molonglo telescope with new feeds, low-noise amplifiers, digital filterbank and FX correlator with the joint aims of: (i) developing and testing SKA-relevant technologies and (ii) providing a new capability for lowfrequency radio astronomy in Australia
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Key features of SKAMP
Collecting area = 1% of SKA (i.e. equivalent to 1 SKA station)
! Multibeaming ! Wide-band line feeds

! Wide instantaneous field of view ! Digital beamforming ! Wide-band FX correlator
(2048 channels)

and LNAs

! Cylindrical antenna prototype ! Adaptive null steering and adaptive noise cancellation

! Frequency and pointing agility
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Target specifications
Parameter Frequency Coverage Bandwidth (BW) Resolution ( < -30°) 1420 MHz 300 MHz 300­1420 MHz 250 MHz 26" x 26" csc|| 123" x 123" csc||

Imaging field of view 1.5° x 1.5° csc|| 7.7° x 7.7° csc|| UV coverage Fully sampled Tsys < 50K < 150K System noise (1) 12 hr: 11 µJy/beam 33 µJy/beam 8 min: 100 µJy/beam 300 µJy/beam Polarisation Dual Linear Correlator I and Q (Full Stokes at 125 MHz BW) Frequency resolution 120­1 kHz (FXF mode: 240 Hz) Independent fanbeam 1.3' x 1.5° 6.2' x 7.7° Indep. fanbeam offset ±6° ±27° Sky accessible in < 1 s 180 deg2 1000 deg2
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Signal Path and Antenna Pattern
Cylindrical Parabolic Collectors
(Two collinear 778 m x 12 m)

300-1420 MHz Feed and LNA
(7,400 feeds, 14,800 LNAs)

Single feed beam Delay line beam Independent fanbeam Imaging beam

Delay line beamforming Analog to Digital Converter Digital delay beamforming
(80 x10 m x 10 m patches)

(1,600 8 bit 250 MHz BW ADCs)

Digital filterbank (160) (Two polarisations @ 250 MHz/patch)
(3,160 baselines, 2,048 channels)

Independent fanbeam Digital Beamformer

FX Correlator

(imaging, spectrometer, searching...)

Signal processing & storage

(64 fanbeams within imaging beam) [Requires extra funding]

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Science outcomes & goals Imaging survey at range of frequencies High redshift HI absorption in galaxies Transient source monitoring Pulsar survey Radio recombination lines & absorption observations of HII regions ! SNR searches ­ ISM structure ! ! ! ! !
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Science goals: High-redshift radio galaxies using continuum data

Radio spectral index measurements using MOST and other catalogues below about 1400 MHz are an efficient way of selecting high-redshift (z>3) radio galaxies (e.g. de Breuck et al. 2000).

Radio galaxy TN0924-2201 at z=5.19
(van Breugel et al. 1999) 15 May, 2003 23


Science goals: HI absorption spectra from distant galaxies

820-870 MHz range and 2048 spectral channel FX correlator enables: · Measurements of HI absorption at z ~ 0.75 that capitalise on the large collecting area of MOST

(Lane 2000) Stage II enables HI measurements at z ~ 0.75, where other methods are not well constrained

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(Lane and Briggs 2001) 24


RFI at Molonglo 200-1500 MHz
(Measured 25 June 2001)

Measured Power (dBm)

-75 -85 -95 -105 -115 0

VHF TV

UHF TV

GSM

500

1000

1500
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Frequency (MHz)
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The Square Kilometre Array (SKA) Project

! Multiple beams & multiple FOV ! Benefits of baseband recording ! http://www.atnf.csiro.au/ska

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Multibeaming with the SKA ! ! Primary beam ­ individual element Field of view ­ continuous image area * whole SKA or sub-array * single station (or core) Multiple beams ­ within FOV

!

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SKA Poster

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Large, imaging Fields of View ! Contiguous FOVs: blind survey over large area, continuous Galactic structures ! HI in emission and the Cosmic web ! Formation & evolution of galaxies: clustering, lensing ! Separated FOVs: parallel projects, deep survey
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Multiple beams ­ in one FOV ! Pulsar timing ! Multiple targets ­ X-ray binaries (XRBs), -ray bursters (GRBs), supernovae (SNe) ! Simultaneous, multi-frequency studies of intra-day variables (IDVs) ! RFI mitigation

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Baseband recording ! By the Nyquist theorem, we can store all the information by sampling at twice the bandwidth and saving the data to tape. ! Expensive on computer time. ! Hold up to 1 hour data in buffer ­ save when triggered, limited to one FOV. ! Targets ­ GRBs, pulsar glitches & timing, SNe, polarisation, RFI mitigation.
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Practical Demonstration of reciprocity

Molonglo Observatory Synthesis Telescope

Light Emitting Analogue of Synthesis Telescope

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