The SKA Molonglo Prototype (SKAMP) Project Molonglo 40th
The SKA Molonglo Prototype (SKAMP) Project Molonglo 40th Anniversary, November 2005 SKA Molonglo Prototype Project (SKAMP) A new low-frequency spectral line instrument. Funded by the ARC, the Science Foundation and the Major National Research Facilities Program. Project Goal: complete signal pathway 2:1 dual polarisation line feed; room temperature electronics; wideband digital signal processing; FX correlator.
Features: wide field of view, imaging, polarisation, spectral line capability, RFI mitigation (adaptive noise cancellation). Strategy: parallel 3-stage re-development of MOST Science & technology prototyping for the Square Kilometre Array (SKA) 1% collecting area, wide-field imaging. What is the SKA? Next generation radio telescope 100 times improvement in many parameters.
Global collaboration. Proposed Australian site in Mileura, WA. Operational 2020. 6 Key science projects. SKAMP Team University of Sydney Anne Green Duncan Campbell-Wilson Adrian Blake
Ludi de Souza Tim Adams Martin Leung Sergey Vinogradov Daniel Mitchell Elaine Sadler 3 site Technical Officers CSIRO ATNF & ICT Michael Kesteven Tony Sweetnam John Bunton Frank Briggs John Kot Argus Technologies
Bevan Jones Martin Owen Peter Liversidge Current Parameters for MOST Single frequency - 843 MHz continuum
3 MHz bandwidth, RHC polarisation 43" spatial resolution 18,000 sq metres collecting area Tsys 55K Field of view: >5 square degrees Sensitivity (7 position switching): 0.8 mJy Sensitivity for full 12 hr: 0.3 mJy Dynamic range: ~200:1 SKAMP 1 (2004 2005) Continuum correlator: 96 station, 4.4 MHz bandwidth, 843 MHz central frequency > 4000 independent baselines, data rate 1sec
Sensitivity 0.8 mJy (12 hrs for complete synthesis; 7-position switching to gain wide field of view) Continuous uv-coverage correlation of interarm & between-arm stations to give good image fidelity Programmable logic chips - FPGAs Tim Adams & John Bunton Continuum correlator 96 independent stations: 88 telescope bays + 2 reference antennas Signal pathway complete commissioning at site Drift scan on sun first light SKAMP 2 (2005 2006)
Spectral-line capability: 830 - 860 MHz with 2048 channels via FX correlator. Existing front end retained 96 stations; full correlation of all stations is highly redundant Unchanged Tsys and angular resolution Optic fibre distribution network designed trenching and conduit completed Field of view roughly 4 square degrees Sensitivity for 12 hrs observation: 0.15 mJy Confusion limit of 0.12 mJy for 43" resolution Spectral line measurements not confusion limited Wide-band uncooled Low Noise Amplifiers
~20K noise temperature Ambient temperature operation Possible extension to operate 300-1400 MHz Design simplified if higher input impedance tolerated (50 input impedance design now) Mass production (8000 units) requires simple assembly design 30 Gain
Gain (dB) 50 40 30 15 Noise Temperature 20 10 0 300 650 Frequency (MHz) 0 1000 Noise Temperature (K)
Prototype 300-1000 MHz HEMT based LNA (Ralph Davison) Molonglo segmented parabola design gives good performance to ~2 GHz Piecewise linear fit to parabola shape y (m) 3x Flat mesh tied on supports at points shown -6 focus 2 1
0 -4 -2 0 x (m) 2 4 6 Mesh supported at 0.6 m (2 ft) intervals in x direction. Each section gives the same error for a linear fit to a parabola. 0.1 dB loss at 1420 MHz. Simulations to test surface approximation
S. Vinogradov SKAMP 3 (2006 2007) Dual polarisation feed module under range test. Next stage to mount on Rapid Prototype Telescope (RPT). Baseline ripples to be measured. First feed prototype 700 1100 MHz. Instantaneous bandwidth 100 MHz. Once prototype approved, construct feeds for complete RPT.
Stage 1 RF beamformer switched delay lines, design set by maximum frequency, ~3length, 100 phase step gives sufficient accuracy. Stage 2 beamforming also in feedline. New mesh will reduce leakage to give Tsys of 40K. 12 hr sensitivity at 843 MHz ~0.1 mJy. Confused! Polarisation not confusion limited (assume 5% mean source value). Wideband feed prototype module 1. 8-element module, 1.4 m length 2. Wide-band dipoles no moving parts 3. Polarisation axes oriented along & across axis of feed better performance than dual-slant feeds 4. Range tested for 700 -1000 MHz Leung Beam & radiation patterns 1. Beam pattern first sidelobe 12dB; cross polarisation -30dB at
meridian, worst at high scan angle, up to -12dB 2. Scanning gain curve flat to 45; cross polarisation -25dB or better Measured element patterns showing gain variation with scan angle (Transverse pol) Measured element patterns showing gain variation with scan angle (Longitudinal pol) 0 0 -5 Normalised E-field (dB) Normalised E-field (dB) -5
-10 -15 -20 -25 -30 3. Transverse illumination pattern HPBW 80; cross polarisation worst at high scan angle, about 15dB Figures show beam patterns and scanning gain variation for the two polarisations, transverse and longitudinal -10 -15
60 80 Rapid Prototype Telescope (RPT) Visit by South African team Double mesh trial reduce leakage Predict improve Tsys to 40K Construction of a 17m bay to test feeds in realistic environment RFI at Molonglo 200-1500 MHz Measured Power (dBm) (Measured 25 June 2001) -75 UHF
TV VHF TV -85 GSM -95 -105 -115 0 500 1000 Frequency (MHz) 1500
RFI measurements in the field at Dept of Defence HQ site Campbell-Wilson, Briggs, Mitchell Dual feed system for 6-m Reference Antenna for adaptive noise cancellation A further extension: uv-coverage with additional stations on NS baselines?? Good image fidelity in 6 hours Small reduction in sensitivity Double survey speed Model for 5 additional stations (Bunton 2005) Key science goals 1. 2.
3. 4. Blind survey of HI absorption in high redshift galaxies initially z~0.7, extend later. Test of mass-assembly of galaxies predictions from CDM scenario. HI in emission measure mass function directly. Redshift range z = 0.17 0.3. Challenging. Cosmic magnetism studies measure diffuse Galactic polarisation and a RM grid from many extragalactic sightlines. High redshift galaxies found as USS sources. Molonglo continuum confusion (10 beams/source) at = 60 Flux Density (mJy)
10 beam size: 112 x 112 csc|| 1 Rengelink et al 1997 WENSS 325 MHz 0.1 beam size: 43 x 43 csc|| Bock et al 1999 SUMSS 843 MHz beam size: 26 x 26 csc|| Wall 1994 1420 MHz 0.01
0 500 1000 Frequency (MHz) 1500 High image fidelity results from good uv-coverage High-dynamic range continuum imaging StageI correlator will allow self-calibration strategies for MOST Current MOST imaging dynamic range is 100200:1 (similar to intrinsic dynamic range of VLA) Self-calibration on VLA
enables imaging dynamic ranges of more than 105:1 (MGPS Green et. al.) Current dynamic range of MOST limits imaging of faint sources, such as filaments of supernova remnants, near bright sources like the Galactic Centre. 1. Blind HI-absorption survey New spectral line capability Measurements of HI absorption at z ~ 0.75 that capitalise on the large collecting area of MOST >10,000 sightlines to search for HI absorption expect to detect ~50 sources in limited redshift range in 2400 sq deg
Few detections eg Darling et al. (2004) of galaxy z=0.78 in front of z=1.992 quasar. (Lane 2000) Stage 2: enables HI measurements at z ~ 0.75, where existing results are not well constrained (Lane and Briggs 2001) When & how is HI assembled into galaxies? (Baugh et al 2004) Data-free zone 2. High-redshift HI emission in galaxies HIPASS (500s)
0.05 0.1 0.15 Redshift z 0.2 0.25 0.3 HI in the nearby Circinus galaxy (Jones et al. 1999) The Molonglo telescope will reach HI mass limits typical of bright spiral galaxies at z=0.2 (lookback time ~3 Gyr), allowing a direct measurement of evolution in the HI mass function. Challenging project.
3. Cosmic Magnetism Magnetism is crucial for : cloud collapse / star formation stellar activity / stellar outflows ISM turbulence / gas motions supernova remnants stability of galactic disks acceleration / propagation / confinement of cosmic rays heating in galaxy clusters AGNs / Jets Proplyd in Orion
SN 1006 MHD turbulence Merger in gal. cluster Magnetism is one of the fundamental forces in Nature, but its role and origin is largely unknown ! Rotation Measure Grid Probes magnetic fields in galaxies, the Milky Way & clusters Rotation measure grid of background sources and polarisation of the diffuse Galactic field 300 RMs through the LMC (Gaensler et al 2004)
4. High-redshift radio galaxies from spectral studies, if lower frequency range implemented Radio spectral index measurements over the range 300 1400 MHz are an efficient way of selecting highredshift (z>3) radio galaxies (e.g. de Breuck et al. 2000, 2004). Radio galaxy TN0924-2201 at z=5.19 (van Breugel et al. 1999) Summary of SKAMP Project status 96-station continuum correlator being commissioned first light. (SKAMP 1)
Optic fibre network conduit laid, fibre on order; spectralline correlator designed and being built, calibration & image processing software being planned. (SKAMP 2) 8-element module of prototype feed under test; RPT nearing mechanical completion; RF beamformers in design. (SKAMP 3) Simulated performance - sensitivity 0.12 mJy for 12 hour observation for 43 resolution, data are confusion limited for continuum images but not for spectroscopy or polarimetry A new lease on life for a mature instrument First Fringes single baseline & interim correlator Team: Green CampbellWilson Kesteven Bunton Adams *Leung
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