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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.
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TheSKAMolongloPrototype(SKAMP)ProjectMolonglo 40th Anniversary,November2005
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.
Anne Green Duncan Campbell-Wilson Adrian Blake Ludi de Souza Tim Adams Martin Leung Sergey Vinogradov Daniel Mitchell Elaine Sadler 3 site Technical Officers Michael Kesteven Tony Sweetnam John Bunton Frank Briggs John Kot Bevan Jones Martin Owen Peter Liversidge SKAMP Team CSIRO – ATNF & ICT University of Sydney Argus Technologies
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 inter-arm & between-arm stations to give good image fidelity • Programmable logic chips - FPGAs
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
50 30 40 30 15 20 10 0 0 Wide-band uncooled Low Noise Amplifiers Prototype 300-1000 MHz HEMT based LNA (Ralph Davison) • ~20K noise temperature • Ambient temperature operation • Possible extension to operate 300-1400 MHz • Design simplified if higher input impedance tolerated (50Ω input impedance design now) • Mass production (8000 units) requires simple assembly design Gain Noise Temperature (K) Gain (dB) Noise Temperature 300 650 Frequency (MHz) 1000
x focus Molonglo segmented parabola design gives good performance to ~2 GHz Piecewise linear fit to parabola shape Flat mesh tied on supports at points shown • 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. • f/D = 0.25
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, ~3l length, 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 • 8-element module, 1.4 m length • Wide-band dipoles – no moving parts • Polarisation axes oriented along & across axis of feed – better performance than dual-slant feeds • Range tested for 700 -1000 MHz Leung
Beam & radiation patterns • Beam pattern – first sidelobe -12dB; cross polarisation -30dB at meridian, worst at high scan angle, up to -12dB • Scanning gain curve – flat to ±45°; cross polarisation -25dB or better • 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
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 25 June 2001) UHF TV VHF TV GSM
RFI measurements in the fieldat 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 • 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.
beam size: 112” x 112” csc|d| Rengelink et al 1997 WENSS 325 MHz beam size: 43” x 43” csc|d| beam size: 26” x 26” csc|d| Bock et al 1999 SUMSS 843 MHz Wall 1994 1420 MHz Molonglo continuum confusion (10 beams/source) at δ= -60°
High-dynamic range continuum imaging StageI correlator will allow self-calibration strategies for MOST Current MOST imaging dynamic range is 100-200:1 (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 ΩHI 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) (12 h) Molonglo (10x12 h) log10 Mlim (HI) (M⊙) Typical bright spiral 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 MHD turbulence Proplyd in Orion Merger in gal. cluster SN 1006 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 high-redshift (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; spectral-line 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
First Fringes – single baseline & interim correlator Team: Green Campbell-Wilson Kesteven Bunton Adams *Leung Blake *Chippendale Vinogradov *Mitchell Briggs Sweetnam Sadler