AMiBA System Performance

1
AMiBA System Performance
Kai-yang Lin1,2 and AMiBA Team1,2,3
1 Institute of Astronomy and Astrophysics,
Academia Sinica, Taiwan 2 Department of Physics,
National Taiwan University, Taiwan 3 Department
of Electronic Engineering, National Taiwan
University
Science Topics for 7-element Array

• Known SZ clusters
• SZ spectral energy distribution
• H0, joint analysis with X-ray
• Baryon fraction, joint analysis with lensing
• Foreground
• Calibration and data processing
• Non-Gaussianity
• CMB primary (not yet observed)
• Performance verification at l1000

Observation Scheme

• Source Tailing, Two-patch subraction
• Separation 2xFWHM of primary beam (45) in RA,
  and 3min in time
• Two patches share the same (az,el) path
• Planet Calibration
• Jupiter, Saturn, Mars were available
• Calibration interval roughly 3hr
• 1? separation between two patches

Wide Bandwidth 4-lag Correlator Performance
Characterization

• Amplitude and phase of the recovered visibility
  from lag-correlator output of a simulated point
  source passing through a baseline. Amplitude and
  phase error for the average of two output
  channels are 5 and 0.3 rad in rms respectively
• Point source flux error after combining different
  baselines varies depending on source position
  away from the phase center.
• Fractional flux error as seen in three annulus
  regions around the phase center are shown in the
  Table below. (Primary beam FWHM22)

Extrapolation of Radio Sources

• 6cm flux density given by PMN or BG6 catalog
• 20cm flux density given by NVSS
• 3mm flux density expected at 94 GHz
• power index derived by fitting 1.4 to 4.85GHz

(src-lead)
On-Off Subtraction

• Plots on the left demonstrate the two-patch
  subtraction. Before subtraction, each patch is
  dominated by pickup of the order of 20Jy/beam.
  After subtracting two patches, a source with
  -0.3Jy flux is revealed.
• Plots on the right show another verification
  using lead-source-trail patches observation. The
  (src-lead) and (src-trail) maps clearly show
  detection of a source in the field center. The
  (lead-trail) map shows nothing significant in the
  center. (Green circle shows the FWHM of primary
  beam blue shaded area indicates the synthesized
  beam)

System Stability
(src-trail)

• Electronics were actively cooled but unregulated
  for the first few months of observation. System
  stability was susceptible to variation of ambient
  temperature.
• Later temperature controls were added to
  correlator box, IF/LO module and 1st section of
  power division in that order.
• Two plots below show the gain and phase of the
  system as checked by measuring visibility of
  Saturn and Jupiter for a whole night. (before
  temperature control)

(lead-trail)
Conclusion

• 6 clusters were observed between Apr and Aug in
  2007.
• On-off subtraction removes most of instrumental
  and/or groun contamination.
• Wide bandwidth and small number of lag is not a
  problem as long as data were properly calibrated.
• Calibration interval of 3hr were used based on
  system stability measurement.
• Radio source contamination is expected to be low
  except for A2261.