The Square Kilometer Array: A global project in Radio Astronomy S. Ananthakrishnan NCRA-TIFR, Pune ASET Colloquium; Tata Institute of Fundamental Research, June 10, 2005.

Radio astronomy has been crucial in discovering phenomena such as quasars, pulsars, superluminal motion and cosmic microwave background. Using radio telescopes one can Using radio telescopes one can observe synchrotron radiation, maser emission as well as bremsstrahlung from thermal gas. Radio waves penetrate dust / gas which absorbs & scatters in most other wavebands. They provide Information on cosmic magnetic fields Radio astronomy techniques provide the highest resolution images in all astronomy Radio astronomy techniques provide the highest resolution images in all astronomy

Thus Radio Astronomy provides unique information about the Universe Non-thermal processes: quasars, radio galaxies, pulsars, masers... Non-thermal processes: quasars, radio galaxies, pulsars, masers... Highest angular resolution: Highest angular resolution: VLBI VLBI Penetrates dust and gas: Penetrates dust and gas:Protostars Galactic nuclei Tracer for Cosmic Magnetic fields Tracer for Cosmic Magnetic fields Beck

Large radio telescopes make discoveries! Quasars and radio galaxies Cosmological evolution of radio sources Cosmic Microwave Background Jets and super-luminal motions Dark matter in spiral galaxies Masers and megamasers - Mass of the blackhole in AGN NGC4258 Pulsars - Gravitational radiation (pulsar timing) - First extra-solar planetary system Serendipity - 21cm HI line

Radio Telescopes  Angular resolving power of a radio telescope is given by ~ /D radians, where =wavelength and D is the aperture diameter.  To get arcsec resolutions, radio astronomers need a radio telescope which is a few hundred km in diameter! Since, this is not practical, the principle of radio interferometry is used, which is analogous to Michelson’s Optical interferometry.

The Ooty Radio Telescope Single frequency; = 92 cm

N As the Earth rotates, 2 antennas placed on the earth offer different projected baselines to a radio source in the sky. By combining many such baselines, one can synthesize a large aperture. Earth Rotation Synthesis Radio Telescope Each pair of antennas functions like Young’s double slit, multiplying the sky brightness distribution by a sinusoidal response function. Thus, an interferometer measures one Fourier component of the radio image.

The Very Large Array, Socorro, New Mexico, USA.

A panoramic view of GMRT array, INDIA.

Low cost 45-m diameter dish of GMRT achieved by a unique design ‘SMART’, which is Stretched Mesh Attached to Rope Truss.

SKA is the next major step in long-term advance of radio astronomy sensitivity.. VLA and GMRT are complementary but use 20 th century technology. Need technology shift to progress !

The original SKA vision: imaging galaxies in HI with <1” resolution  ~100x sensitivity of VLA  ~1 square kilometre collecting area  study local galaxy dynamics in detail  detect galaxies at high redshift in HI and in synchrotron emission NGC 4151 VLA 18 hours HI at 5 arcsec resolution current state-of-the-art (Image from Mundell et al.)

SKA’s basic specifications follow the original vision Sensitivity: x VLA at same wavelength  Brightness sensitivity ~1KSensitivity: x VLA at same wavelength  Brightness sensitivity ~1K It will become the world’s Premier Imaging Instrument ! Huge advantages for SKA Huge change for radioastronomy Frequency coverage: ~150 MHz to ~22 GHz Max. Resolution: <0.1 arcsec to exceed HST, NGST, ALMA Field-of-view: >1 square degree

…….. Specifications Multibeam (at lower frequencies) Multibeam (at lower frequencies) Need innovative design to reduce cost Need innovative design to reduce cost International funding unlikely to exceed $1000m International funding unlikely to exceed $1000m 10 6 sq metre => $1000 / sq metre 10 6 sq metre => $1000 / sq metre cf VLA $10,000 / sq metre (50GHz) cf VLA $10,000 / sq metre (50GHz) GMRT $1,000 / sq metre (1GHz) GMRT $1,000 / sq metre (1GHz) ATA $2,000/sq metre (11GHz) ATA $2,000/sq metre (11GHz)

Achieving the SKA vision… Reduce overall cost per m 2 of collecting area by a factor ~10 compared to current arrays Maximising flexibility of design While… Minimising maintenance/running costs And…  Take advantage of massive industrial R&D in fibre optics and electronics industries (“Moore’s Law” to ~2015) for transport and handling of data  Develop innovative new concepts for collectors

Phased array concept Basic idea: replace mechanical pointing & beam forming by electronic means

Multi beams Synthesized beams Station antenna patterns Element antenna pattern Observing teams with their own beams Observing teams with their own beams like particle accelerator, but can have all beams simultaneously like particle accelerator, but can have all beams simultaneously

SKA Poster

VLA Future Sensitivity HST SKA 2017

To achieve this sensitivity we need: HEMT receivers HEMT receivers wide band, cheap, small and reliable wide band, cheap, small and reliable Can build low noise systems with many elements Can build low noise systems with many elements Focal plane arrays Focal plane arrays Field of view Field of view Interference rejection Interference rejection adaptive nulling can work in single dishes and arrays adaptive nulling can work in single dishes and arrays More computing capacity More computing capacity computing power doubles every 18 months (Moore’s Law) computing power doubles every 18 months (Moore’s Law) Software time scales are much longer Software time scales are much longer it becomes a capital cost ! it becomes a capital cost !

InP devices 12mm3mm

Radio Frequency Interference The Challenge The Challenge Sensitivity to increase (100x) Sensitivity to increase (100x) current regulations will be inadequate current regulations will be inadequate Whole of radio spectrum needed Whole of radio spectrum needed 2% of spectrum is reserved for Radio Astronomy 2% of spectrum is reserved for Radio Astronomy early Universe studies require “whole” spectrum, but only to “listen”, and only from a few locations. early Universe studies require “whole” spectrum, but only to “listen”, and only from a few locations. LEO telecom satellites a new threat LEO telecom satellites a new threat no place on Earth free from interference from sky no place on Earth free from interference from sky OECD task force on Radio Astronomy OECD task force on Radio Astronomy

Terrestrial Interference FORTÉ satellite: 131 MHz Forte satellite: 131MHz

Interference excision Receiver- A/D adaptive algorithm DBF Control source RFI Positioner D/A spectrum analyser 8811  c i A i cici AiAi (  )

Object Oriented Software AIPS++AIPS++ Astronomical Image Processing System Astronomical Image Processing System C++, scripting, GUI’s, libraries, toolkits and applications C++, scripting, GUI’s, libraries, toolkits and applications Designed by a team of astronomers and programmers Designed by a team of astronomers and programmers

6 proposals have been presented for the SKA design - Array of Cylindrical reflectors : Australia -Array of large reflectors : Canada : LAR; China : KARST - Planar phased array : Europe : THEA -Array of small dishes : India : PPD; USA : Hydroform dishes Costs are between 1- 2 G$ International comparison: A modern bridge: 5 G$ 100 km Highway: 2 G$ SKA proposals

frequency

Indian Design: 12-m PPD Antenna PPD consists of a central hub of diameter 4 m 24 elastically bent stainless steel tubes with 8 mm wall thickness and 40 mm O.D. an outer circumferential ring to hold the elastically bent radial tubes of 40 mm O.D. an intermediate ring of 40 mm O.D. 103 stations of 9 x 9 PPD  8343 dishes. Frequency up to 8 GHz.

… USA Design

An example of a SKA configuration 200km Not a single 1 km square aperture ! a wide range of baselines

Science with the SKA The Universe in the Dark Ages The Universe in the Dark Ages redshifted HI redshifted HI Star formation Star formation epoch of (re-)ionization epoch of (re-)ionization Cosmology and Large Scale Structure Cosmology and Large Scale Structure Gravitational Lensing Gravitational Lensing Gamma Ray bursters Gamma Ray bursters AGN - VLBI AGN - VLBI Stellar radio astronomy Stellar radio astronomy Pulsars Pulsars Solar system Solar system SETI SETI

Evolution of star formation rates Starburst galaxies e.g. M82 -Radio reveals starburst region through dust -VLBI resolves expanding supernovae -Infer star birth rate from death rate more directly than other means -Calibrate integrated radio continuum  SFR at high z SKA can do this at any redshift  Cosmological history of star formation M82 VLA+ MERLIN+VLBI M82 optical

Epoch of reionization Avery Meiksen

Imaging Normal Galaxies at high z…a basic goal of SKA H2OH2O Neutral Hydrogen Continuum CO In continuum HI & CO In continuum HI & CO SKA sensitivity  radio image of any object seen in other wavebands SKA sensitivity  radio image of any object seen in other wavebands Not effected by dust obscuration Not effected by dust obscuration Resolution advantage Resolution advantage cf. ALMA, NGST, HST cf. ALMA, NGST, HST Radiometric redshifts Radiometric redshifts

Interstellar Scintillation Frail & Kulkarni Frail & Kulkarni VLA 8GHz VLA 8GHz Scintillates if Scintillates if  < 10  as  < 10  as Calibrate of field SNR’s Calibrate of field SNR’s Only 1 GRB strong enough in 4 years Only 1 GRB strong enough in 4 years Many days integration Many days integration

SKA’s 1 o field-of-view HST SKA 6cm ALMA 15 Mpc at z = 2 SKA 20 cm for surveys and transient events in 10 6 galaxies !

To summarize the present status Netherlands: LOFAR (phased array R&D) Netherlands: LOFAR (phased array R&D) Canada: Large Adaptive Reflector (flat panels, tethered balloon) Canada: Large Adaptive Reflector (flat panels, tethered balloon) China: KARST (Array of Arecibo's) China: KARST (Array of Arecibo's) US consortium: ATA (300 x 5m dishes, 1-10 GHz) US consortium: ATA (300 x 5m dishes, 1-10 GHz) US NRAO: VLA upgrade - paths to SKA? US NRAO: VLA upgrade - paths to SKA? Australia: Cylindrical reflector GHz Australia: Cylindrical reflector GHz India: Lower cost dishes with fine meshes. India: Lower cost dishes with fine meshes.

SKA International Steering Committee 18 members representing 11 countries 18 members representing 11 countries 6 European (UK, Germany, Netherlands, Sweden, Italy, Poland) 6 European (UK, Germany, Netherlands, Sweden, Italy, Poland) 6 United States 6 United States 2 Canada 2 Canada 2 Australia 2 Australia 1 China 1 China 1 India 1 India MOU signed IAU Manchester August 2000 MOU signed IAU Manchester August 2000 New membership requests New membership requests Russia, Sth Africa, Japan Russia, Sth Africa, Japan

ISSC: SKA planning schedule

Thank you