The Square Kilometer Array: A global project in Radio Astronomy

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The Square Kilometer Array A global project in
Radio Astronomy
ASET Colloquium Tata Institute of Fundamental
Research, June 10, 2005.

• S. AnanthakrishnanNCRA-TIFR, Pune 411007

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

• 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

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Thus Radio Astronomy provides unique information
about the Universe

• Non-thermal processes quasars, radio galaxies,
  pulsars, masers...
• Highest angular resolution
• VLBI
• Penetrates dust and gas
• Protostars
• Galactic nuclei
• Tracer for Cosmic Magnetic fields

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Large radio telescopes make discoveries!

• Quasars and radio galaxies

• Serendipity

- 21cm HI line

• 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
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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 Michelsons Optical
  interferometry.

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The Ooty Radio Telescope
Single frequency ? 92 cm
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Earth Rotation Synthesis Radio Telescope
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.
Each pair of antennas functions like Youngs
double slit, multiplying the sky brightness
distribution by a sinusoidal response function.
Thus, an interferometer measures one Fourier
component of the radio image.
N
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The Very Large Array, Socorro, New Mexico, USA.
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A panoramic view of GMRT array, INDIA.
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Low cost 45-m diameter dish of GMRT achieved by a
unique design SMART, which is Stretched Mesh
Attached to Rope Truss.
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SKA is the next major step in long-term advance
of radio astronomy sensitivity..


VLA and GMRT are complementary but use 20th
century technology.
Need technology shift to progress !

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The original SKA vision imaging galaxies in HI

with lt1 resolution
NGC 4151 VLA 18 hours
current state-of-the-art
HI at 5 arcsec resolution
(Image from Mundell et al.)
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SKAs basic specifications follow the original
vision

• Sensitivity 50--100x VLA at same wavelength
  ?Brightness sensitivity 1K

Huge change for radioastronomy

• Frequency coverage 150 MHz to 22 GHz

Huge advantages for SKA

• Field-of-view gt1 square degree

• Max. Resolution lt0.1 arcsec to exceed
• HST, NGST, ALMA

It will become the worlds Premier Imaging
Instrument !
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.. Specifications

• Multibeam (at lower frequencies)
• Need innovative design to reduce cost
• International funding unlikely to exceed 1000m
• 106 sq metre gt 1000 / sq metre
• cf VLA 10,000 / sq metre (50GHz)
• GMRT 1,000 / sq metre (1GHz)
• ATA 2,000/sq metre (11GHz)

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Achieving the SKA vision

• Reduce overall cost per m2 of collecting area
  by a factor 10 compared to current arrays

While

• Maximising flexibility of design

And

• Minimising maintenance/running costs

?Take advantage of massive industrial RD in
fibre optics and electronics industries
(Moores Law to 2015) for transport and
handling of data
? Develop innovative new concepts for collectors
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Phased array concept
Basic idea replace mechanical pointing beam
forming by electronic means
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Multi beams
Element antenna pattern
Station antenna patterns
Synthesized beams
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• Observing teams with their own beams
• like particle accelerator, but can have all beams
  simultaneously

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SKA Poster
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Future Sensitivity
HST
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To achieve this sensitivity we need

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

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InP devices

• 12mm 3mm

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Radio Frequency Interference

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

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Terrestrial Interference

• Forte satellite 131MHz

FORTÉ satellite 131 MHz
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Interference excision
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Object Oriented Software

• AIPS
• Astronomical Image Processing System
• C, scripting, GUIs, libraries, toolkits and
  applications
• Designed by a team of astronomers and programmers

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SKA proposals

• 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

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frequency
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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.
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USA Design
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An example of a SKA configuration
Not a single 1 km square aperture !
a wide range of baselines
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Science with the SKA

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

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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 optical
M82 VLA MERLINVLBI
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Epoch of reionization
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Imaging Normal Galaxies at high za basic goal
of SKA

• In continuum HI CO
• SKA sensitivity ? radio image of any object seen
  in other wavebands
• Not effected by dust obscuration
• Resolution advantage
• cf. ALMA, NGST, HST
• Radiometric redshifts

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InterstellarScintillation

• Frail Kulkarni
• VLA 8GHz
• Scintillates if
• ? lt 10 ?as
• Calibrate of field SNRs
• Only 1 GRB strong enough in 4 years
• Many days integration

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SKAs 1o field-of-view

• for surveys and transient events in 106 galaxies !

SKA 20 cm
15 Mpc at z 2
ALMA
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To summarize the present status

• Netherlands LOFAR (phased array RD)
• Canada Large Adaptive Reflector (flat panels,
  tethered balloon)
• China KARST (Array of Arecibo's)
• US consortium ATA (300 x 5m dishes, 1-10 GHz)
• US NRAO VLA upgrade - paths to SKA?
• Australia Cylindrical reflector 0.3 - 5 GHz
• India Lower cost dishes with fine meshes.

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SKA International Steering Committee

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

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ISSC SKA planning schedule
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Thank you