the square kilometer array: a global project in radio astronomy
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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.. SpecificationsMultibeam (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 costsAnd…
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 conceptBasic 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 InterferenceThe ChallengeThe Challenge
Sensitivity 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 Astronomyearly 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
H2ONeutral 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 a
t 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
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