THE NEED FOR A SQUARE KILOMETER ARRAY

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					    THE NEED FOR A SQUARE
      KILOMETER ARRAY
        For the US SKA Consortium
            Jim Cordes, Cornell University
                CfA talk, 3 April 2001

 What is the SKA?
 Why build the SKA?
 Science Goals & Payoffs
 Configurations, Modes and Sites
 Development Plan (International, US)
             The SKA Concept
Initiated in early 1990s through considerations of:
  • high redshift science
  • needed sensitivity (Ae / Tsys)
  • coverage of obs. phase space for many science goals
  • complementarity with other 
     (LOFAR, EVLA, ATA, ALMA, LSST, VLT, NGST,
    EXIST, GLAST, CELT, OWL . . . )
  • advances in digital hardware & RF devices
  • mitigation of RFI  innovation needed
China KARST        Current Concepts

Canadian
aerostat


US Large N
               (cf. Allen Telescope Array,
                   Extended VLA)

Australian
Luneburg
Lenses

               (cf. LOFAR = Low Freqency
Dutch fixed    Array)
planar array
Photos:
R.N.
Manchester
Canadian Aerostat & Paraboloid
China KARST        Current Concepts

Canadian
aerostat


US Large N
               (cf. Allen Telescope Array,
                   Extended VLA)

Australian
Luneburg
Lenses

               (cf. LOFAR = Low Freqency
Dutch fixed    Array)
planar array
             Previous Actions
•   1993   URSI Large Telescope Working Group
•   1997   International Memo. of Agreement
•   1997-  Workshops on science & technology
•   1999   US SKA Consortium established to
           mobilize US participation
• late 90s Endorsements by review panels
           (Australia, Canada, China, Eur. Union)
• 1999- Presentations to Decadal Review Panel
           (Jackie Hewitt)
Astronomy & Astrophysics in
     the New Millenium
Recommends:
“…that a program be established to plan
and develop technology for the Square
Kilometer Array, an international
centimeter wavelength radio telescope for
the second decade of the century.”
Current Baseline Specifications
Parameter            Design Goal               Comments
Sensitivity          A/T = 2 x 104 m2 / K      20x Arecibo, 75x VLA
Surface brightness   1K at 0.1 arcsec (cont)
Point sources        0.5 Jy                   10 in 1 day, 100 MHz
Frequency range      0.15 – 22 GHz
Redshift coverage    Z < 8.5 HI,
                     Z > 4.2 CO (10)
L* galaxies          Zmax ~ 2 HI, ~ 20 CO
FOV (imaging)        1 degree2 at 1.4 GHz
Multibeams           > 100
Ang. Resolution      40 mas at 1.4 GHz         VLBI: SKA enables all-sky
                                               phase referencing
Pixels               108
Instantaneous        20% at high frequencies
bandwidth
Spectra channels     104
Image Dynamic        106 at 1.4 GHz
Range
Polarization         -40 dB
isolation
                   Figures of merit for
                   current telescope
   SKA     VLBI    developments
             SKA   Circle radius = target or best
                   Arrows:
   SKA     SKA           Blue = current best
                         Cyan = target


   BATSE   GLAST               VLTI, KECKI




GLAST                          CELT,OWL
           GLAST
           Key Science Areas
•   High Redshift Universe
•   Transient Universe
•   Galactic Census
•   Solar System Inventories

Science document (c. 1998):
Science with the SKA: A Next Generation World Radio
Observatory (AR Taylor, R Braun)

http://www.skatelescope.org/ska_science.shtml
        The High-z Universe
• End of the Dark Ages:          z ~ 6 - 20 (?)
• Resolution:                    0.1 arcsec ~ 1 kpc
                                              (z=1)
• Identify:
      • pregalactic structures
      • competition between mergers and galaxy
           winds (size, mass distributions)
      • distribution of luminous matter w.r.t. dark
             matter potentials
       The High-z Universe
Detectability:
 1. 21-cm HI out of equilibrium with CBR
 2. Earliest star bursts (synchrotron)
 3. Early CO (z > 4.2 for 10, 8.4 for 2 1)

 HI Column Densities: 1017 cm-2
 Typical L* galaxy to z~2
               ~ 105 galaxies / deg2
                rotation curves to z~1
 CO: L* to z~20 (should they exist!)
    The High-z Universe (2)
Other High-z Science:

• Large scale structure studies
• Gravitational lensing of large samples
• Weak-lensing studies of dark matter dist’ns.
• Tests of the unified AGN model and routine
       polarization mapping (m.a.s. and larger)
• Megamasers to z~2 (OH) and z~0.15 (H2O) to
     track merger activity.
       TRANSIENT SOURCES
Sky Surveys:
The X-and--ray sky has been monitored highly
successfully with wide FOV detectors
(e.g. RXTE/ASM, CGRO/BATSE).


The transient radio sky (e.g. t < 1 month) is largely
unexplored.


New objects/phenomena are likely to be discovered
as well as the predictable classes of objects.
     TRANSIENT SOURCES (2)
TARGET OBJECTS:
• Neutron star magnetospheres
• Accretion disk transients (NS, blackholes)
• Supernovae
• Gamma-ray burst sources
• Brown dwarf flares (astro-ph/0102301)
• Planetary magnetospheres & atmospheres
• Maser spikes
• ETI
     TRANSIENT SOURCES (3)
Certain detections:
• Analogs to giant pulses from the Crab pulsar out
      to ~5 Mpc
• Flares from brown dwarfs out to at least 100 pc.
• GRB afterglows to 1 µJy in 10 hours at 10 .
Possibilities:
• -ray quiet bursts and afterglows?
• Intermittent ETI signals?
• Planetary flares?
OBSERVABLE DISTANCES OF CRAB PULSAR’S
            GIANT PULSES
      Methods with the SKA
 I.   Target individual SNRs in galaxies to
      5-10 Mpc

II. Blind Surveys: trade FOV against
    gain by multiplexing SKA into
    subarrays.

III. In all cases, exploit coincidence tests to
      ferret out RFI
        Milky Way Census
Targets: Molecular cloud regions
          YSOs, jets
          Main sequence stars (thermal!)
          Evolving & evolved stars
Full Galactic Census:
          microquasars
          radio pulsars (P-DM searches,
                SKA-VLBI astrometry)
          SNR-NS connections (SGRs,
                magnetars, etc.)
Surveys
with Parkes,
Arecibo &
GBT.


Simulated &
actual


Yield ~ 2000
pulsars.
SKA pulsar
survey


600 s per
beam


~104 psr’s
                    Pulsar Yield
Up to 104 pulsars (~105 in MW, 20% beaming)
NS-NS binaries (~ 100, merger rate)
NS-BH binaries (?)
Planets, magnetars etc.
Pulsars as probes of entire Galaxy:
  •   spiral arms
  •   pulsar locations vs. age
  •   electron density map (all large HII regions sampled)
  •   magnetic field map from Faraday rotation
  •   turbulence map for WIM (warm ionized medium)
   Solar System Inventories:
   KBOs & Tracking NEOs
• Thermal detection of KBOs out to
    100 AU (> 350 km)

     SKA needs to go to ~20 GHz

• Orbital elements of NEOs (>200m):

    SKA as receiver element of bistatic
    radar configuration
The Main Technology Challenges

  1. Cost per unit Ae / Tsys
    – Arecibo (~$150M)             $3G
    – EVLA I (~$200M)              $15G




 Need to reduce costs to < $1G    ( 5 to 15)
The Main Technology Challenges
2. Fully digital solutions to:
  –   sampling
  –   beam forming
  –   RFI rejection
  –   signal processing
       • real time
       • post processing



 Concept studies + Moore’s Law
The Main Technology Challenges

3. Promoting & Maintaining radio-quiet sites.




 Campaigning & working with governmental
  and international agencies and industry.
  The Main Technology Challenges

4. Operations & Data Management of a highly
    multiplexed, wide-bandwidth instrument.



  Automated operations, large-scale data
   mining and storage.
          Future Timeline (1)
• 2001   White Paper to NSF for technology
         development ( 2006)
• 2002   Prioritized science goals (international)
         Design requirements
         SKA Management Plan established
• 2003   Strawman designs
         Site requirements
• 2005   Design Choice
         Site selection
          Future Timeline (2)

• 2006-2010:   Prototype array(s)
• 2010         SKA construction begins
• 2015         Completion