The Square Kilometer Array:The Square Kilometer Array: A global project in Radio AstronomyA global project in Radio Astronomy

S. AnanthakrishnanS. AnanthakrishnanNCRA-TIFR, Pune 411007NCRA-TIFR, Pune 411007

ASET Colloquium; Tata Institute of Fundamental Research, June 10, 2005.

Radio astronomy has been crucial in discovering phenomena Radio astronomy has been crucial in discovering phenomena such as quasars, pulsars, superluminal motion and cosmic such as quasars, pulsars, superluminal motion and cosmic microwave background. microwave background.

• Using radio telescopes one canUsing 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 Radio astronomy techniques provide the highest the highest resolution images resolution images in all astronomyin all astronomy

Thus Radio Astronomy provides Thus Radio Astronomy provides unique information about the Universe unique information about the Universe

Non-thermal processes: quasars, radio Non-thermal processes: quasars, radio galaxies, pulsars, masers...galaxies, pulsars, masers...

Highest angular resolution: Highest angular resolution: VLBIVLBI

Penetrates dust and gas: Penetrates dust and gas: ProtostarsProtostars

Galactic nucleiGalactic nuclei

Tracer for Cosmic Magnetic fieldsTracer for Cosmic Magnetic fields

Beck

Large radio telescopes Large radio telescopes make discoveries!make discoveries!

Quasars and radio galaxies

Cosmological evolution of radio sourcesCosmic Microwave BackgroundJets and super-luminal motionsDark matter in spiral galaxiesMasers and megamasers

- Mass of the blackhole in AGN NGC4258Pulsars

- Gravitational radiation (pulsar timing)- First extra-solar planetary system

Serendipity - 21cm HI line

Radio TelescopesRadio Telescopes

Angular resolving power of a radio telescope Angular resolving power of a radio telescope is given by is given by ~~//DD radians, where radians, where =wavelength =wavelength and and DD is the aperture diameter. is the aperture diameter.

To get arcsec resolutions, radio astronomers To get arcsec resolutions, radio astronomers need a radio telescope which is a few hundred need a radio telescope which is a few hundred km in diameterkm in diameter!! Since, this is not practical, the Since, this is not practical, the principle of radio interferometry is used, principle of radio interferometry is used, which is analogous to Michelson’s Optical which is analogous to Michelson’s Optical interferometry.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 SKA is the next major step in long-term advance of radio astronomy sensitivity..advance of radio astronomy sensitivity..

VLA and GMRTare complementary but use 20th century technology.

Need technology shift to progress !

The original SKA vision: The original SKA vision: imaging galaxies in HIimaging galaxies in HI with <1” resolution 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 visionSKA’s basic specifications follow the original vision

• Sensitivity:Sensitivity: 50--100x VLA at same wavelength 50--100x VLA at same wavelength Brightness sensitivity ~1KBrightness sensitivity ~1K

It will become the world’s Premier Imaging Instrument !

Huge advantagesfor SKA

Huge changefor 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.. 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 International funding unlikely to exceed

$1000m$1000m101066 sq metre => $1000 / sq metre 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…Achieving the SKA vision…• Reduce overall cost per m2 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 conceptPhased array concept

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

Multi beamsMulti beams

4

8

12

16Synthesized beams

Station antenna patterns Element antenna pattern

Observing teams Observing teams with their own beamswith their own beams like particle like particle

accelerator, but can accelerator, but can have all beams have all beams simultaneouslysimultaneously

SKA PosterSKA Poster

VLA

Future SensitivityFuture Sensitivity

HST SKA2017

To achieve this sensitivity we need:To achieve this sensitivity we need:HEMT receiversHEMT receivers

wide band, cheap, small and reliablewide band, cheap, small and reliableCan build low noise systems with many elementsCan build low noise systems with many elements

Focal plane arraysFocal plane arraysField of viewField of view

Interference rejectionInterference rejectionadaptive nulling can work in single dishes and arraysadaptive nulling can work in single dishes and arrays

More computing capacityMore computing capacitycomputing power doubles every 18 months (Moore’s Law)computing power doubles every 18 months (Moore’s Law)Software time scales are much longerSoftware time scales are much longer

it becomes a capital cost !it becomes a capital cost !

InP devicesInP devices

12mm12mm 3mm3mm

Radio Frequency InterferenceRadio Frequency Interference

The ChallengeThe ChallengeSensitivity to increase (100x)Sensitivity to increase (100x)

current regulations will be inadequatecurrent regulations will be inadequate

Whole of radio spectrum neededWhole of radio spectrum needed2% of spectrum is reserved for Radio Astronomy2% of spectrum is reserved for Radio Astronomy

early Universe studies require “whole” spectrum, but early Universe studies require “whole” spectrum, but only to “listen”, and only from a few locations.only to “listen”, and only from a few locations.

LEO telecom satellites a new threatLEO telecom satellites a new threatno place on Earth free fromno place on Earth free from interference from skyinterference from sky

OECD task force on Radio AstronomyOECD task force on Radio Astronomy

Terrestrial Interference

FORTÉ satellite: 131 MHz

Forte satellite: 131MHzForte satellite: 131MHz

Interference excisionInterference excision

Receiver- A/D

adaptivealgorithm

DBF

Control

source

RFI Positioner

D/A

spectrum analyser

8 8 1 1

ci Ai

ci

Ai

() ()

Object Oriented SoftwareObject Oriented Software

• AIPS++ AIPS++ • Astronomical Image Processing SystemAstronomical Image Processing System

• C++, scripting, GUI’s, libraries, toolkits and C++, scripting, GUI’s, libraries, toolkits and applicationsapplications

• Designed by a team of astronomers and Designed by a team of astronomers and programmersprogrammers

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 AntennaIndian Design: 12-m PPD Antenna

PPD consists of PPD consists of

a central hub of a central hub of diameter 4 mdiameter 4 m

24 elastically bent 24 elastically bent stainless steel stainless steel tubes with 8 mm tubes with 8 mm wall thickness and wall thickness and 40 mm O.D.40 mm O.D.

an outer an outer circumferential circumferential ring to hold the ring to hold the elastically bent elastically bent radial tubes of 40 radial tubes of 40 mm O.D. mm O.D.

an intermediate ring an intermediate ring of 40 mm O.D.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 An example of a SKA configurationconfiguration

200km

Not a single 1 km square aperture !

a wide range of baselines

Science with the SKAScience with the SKA The Universe in the Dark AgesThe Universe in the Dark Ages

redshifted HIredshifted HIStar formationStar formationepoch of (re-)ionizationepoch of (re-)ionization

Cosmology and Large Scale StructureCosmology and Large Scale StructureGravitational LensingGravitational Lensing

Gamma Ray burstersGamma Ray bursters AGN - VLBIAGN - VLBI Stellar radio astronomyStellar radio astronomy PulsarsPulsars Solar systemSolar system SETISETI

Evolution of Evolution of star formation ratesstar 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 opticalM82 optical

Epoch of reionizationEpoch of reionization

Avery MeiksenAvery Meiksen

Imaging Normal GalaxiesImaging Normal Galaxies at high z…a basic goal of SKA at high z…a basic goal of SKA

H2O

Neutral Hydrogen

Continuum

CO

In continuum HI & COIn continuum HI & CO SKA sensitivity SKA sensitivity radio radio

image of any object image of any object seen in other seen in other wavebandswavebands

Not effected by dust Not effected by dust obscurationobscuration

Resolution advantage Resolution advantage cf. ALMA, NGST, HSTcf. ALMA, NGST, HST

Radiometric redshiftsRadiometric redshifts

InterstellarInterstellarScintillationScintillation

Frail & KulkarniFrail & Kulkarni VLA 8GHzVLA 8GHz Scintillates if Scintillates if < 10 < 10 asas Calibrate of field Calibrate of field

SNR’sSNR’s Only 1 GRB strong Only 1 GRB strong

enough in 4 yearsenough in 4 years Many days Many days

integrationintegration

SKA’s 1SKA’s 1oo field-of-view field-of-view

HST SKA 6cm

ALMA

15 M

pc

at

z =

2 SKA 20 cm

for surveys and transient events for surveys and transient events in 10in 106 6 galaxies !galaxies !

To summarize the present statusTo summarize the present statusNetherlandsNetherlands:: LOFAR (phased array R&D) LOFAR (phased array R&D)

Canada:Canada: Large Adaptive Reflector (flat Large Adaptive Reflector (flat panels, tethered balloon)panels, tethered balloon)

China:China: KARST (Array of Arecibo's)KARST (Array of Arecibo's)

US consortium: US consortium: ATA (300 x 5m dishes, 1-10 ATA (300 x 5m dishes, 1-10 GHz)GHz)

US NRAO: US NRAO: VLA upgrade - paths to SKA?VLA upgrade - paths to SKA?

Australia: Australia: Cylindrical reflector 0.3 - 5 GHzCylindrical reflector 0.3 - 5 GHz

India:India: Lower cost dishes with fine meshes.Lower cost dishes with fine meshes.

SKA International Steering SKA International Steering CommitteeCommittee

18 members representing 11 countries18 members representing 11 countries 6 European (UK, Germany, Netherlands, Sweden, Italy, Poland)6 European (UK, Germany, Netherlands, Sweden, Italy, Poland) 6 United States6 United States 2 Canada 2 Canada 2 Australia2 Australia 1 China1 China 1 India1 India

MOU signed IAU Manchester MOU signed IAU Manchester August 2000August 2000

New membership requestsNew membership requests Russia, Sth Africa, JapanRussia, Sth Africa, Japan

ISSC: SKA planning scheduleISSC: SKA planning schedule

Thank youThank you