Transcript EoR - CAASTRO

Global EoR Experoments
Ron Ekers, CSIRO
CAASTRO Global EoR Workshop
Uluru, 17 July 2013
Summary
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Strategy for technically difficult experiments
– Either masochists or people who don’t know any better!
– NB the Crick and Watson story on DNA structure
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Global HI EoR v imaging HI EoR
– Statistical v direct detection
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CORE  ZEBRA  SARAS
Other global HI experiments
– EDGES, BIGHORNS, COREII, DARE,
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Pulse calibration
Epoch of (re)combination
July 2013
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Peter
Shaver
conjecture
Global HI EoR prediction
Pritchard et al, Nature 468, 772 (2010)
(200/65)2.5=17
Z = 6.3
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The 21cm EoR challenge
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Global T ~30mK in few MHz
– S/N easy – can reach a few mK in few hours
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T/T < 10-4 to10-5
Zero spacing
Calibrate the complex gain
interferometer
Minimize the number of unknowns that can couple to EoR
Remove the forgrounds
Remove the additive constant
– Correlation receiver
» Eliminate LNA additive noise
– Position switching
» T now very small so large antenna and long integration times
» Correlation interferometer
» Arrays
• Statistical detection
• Direct detection
CSIRO
From CoRE to ZEBRA
CoRE (Chippendale)
RRI
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ZEBRA  SARAS
MRO
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Calibratable
receiver
ZEBRA II
July 2013
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CORE
frequency independent antenna beam
Global EoR system
RRI Bangalore
Ravi
Subrahmanyan
Peter
Shaver
A.
Raghunathan
Ron
Ekers
Zebra – fat dipole v1
ZEBRA Global EoR Experiment
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ZEro-spacing
measurement of the
Background RAdio
spectrum
Partially reflecting
resistive screen
Virtual zero spacing
interferometer
Removes all additive
errors
Modulate screen ?
Subrahmanyan,
Ekers
Patra
Partial
reflector/transmitter
X
The space beam-splitter:
a resistive wire mesh
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Need a space beam-splitter before the antenna
A lossless screen (e.g. a conducting grid)
– transmitted & reflected waves are orthogonal
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Resistive wire mesh
– Thickness of wire < skin depth
– Frequency independent
– Re-radiated fields no longer cancel the incident field on
the far side of the wire screen
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Lumped resistance on scale << 
– Practical solution instead of resistance wire
Building resistive screen
The Resistive Screen
copper wire + lumped resistors
resistor value
= free space impedance/2
3x4 metres
holes to reduce wind loading
Roll up for transport
ZEBRA – interferometer
first CMB correlation 20 Jan 2011
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3.4m
1.5m separation
Max sky coverage at zero spacing
26%
Contributions to correlated output
– Global sky signal
– Screen radiating
– 1.5m interferometer sky
correlation
» One path through screen
» Both paths miss screen
Ferrite absorber
ZEBRA at Gauribidanur
Zebra correlated output
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Baseline ripple
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changes with LST
Repeats each day
Multipath scattering of galaxy foreground signal
Shifted location …….
SARAS receiver evolution
SARAS receiver
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Patra & Subramanyan, EA (2013)
88-175MHZ
Differential correlation spectrometer
Digital correlator well separated from
receiver
Minimize number of parameters in
solution (11)
Solve for multipath propagation from
internal reflections
Eg noise from receiver input
SARAS internal reflections
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Short connections to keep broad bandwidth
Long connections to decrease coupling
SARAS internal reflections
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Short connections to keep broad bandwidth
Long connections to decrease coupling
SARAS waterfall plot
Pulse calibration ?
Pulse injected at Parkes vertex
Pulse reflected from Parkes focus
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Inject and integrate short (sec) pulses
Calibrated noise spectrum
Understand & calibrate reflections
Nipanjana Patra, Paul Roberts
Pulse calibration
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Band limited pulse with -20db reflection
Pulse repetition rate 106 Hz
Accuracy 0.05%
Other Global EoR Experiments
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WSRT:
– Lunar occultation
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EDGES: Rogers & Bowman
– Polynomial fits Δz > 0.06
– Absolute calibration of components for wider bandwidths
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BIGHORNS: Sokolowski, Tremblay, Wayth, Tingay ⑫
– Low rfi site, high stability
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Core II: Bannister, Chipendale, Dunning ①
– Precision self calibrating receiver
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DARE
– Go to moon to avoid ionosphere and rfi
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Rogers & Bowman (EDGES memo #99)
Estimates of the sources
of error and their
magnitude expressed as
the residuals to fits with
increased numbers of
parameters along with the
bias in EOR estimation
Parameters of 10 parameter
solution:
1] EoR signature
(30 mK, 50@145MHz)
2] scale (assumes spectral index of -2.5)
3] constant (ground emission)
4] frequency -2 (ionosphere emission)
5] frequency -4.5 (ionosphere absorption)
6] Magnitude of antenna S11
7] Magnitude of LNA S11
8] S11 phase error
9] S11 delay error
10] temperature scale
Estimate of errors using simulations – for more details see EDGES memo 99
BIGHORNS
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Sokolowski, Tremblay, Wayth,
Tingay ⑫
– Low rfi site, high stability
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Dynamic spectrum
normalised by the median
Dynamic range 2%
– Required 10-4
Day
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200MHz
CORE2: A global EOR experiment with a selfcalibrating receiver on two antennas
CORE2-DISH
5 Degree beam
Optimised for foreground removal
CORE2-MONO
60 Degree beam
Optimised for frequency
Independence and low RFI and
CORE2: A global EOR experiment with a self-calibrating receiver and two antennas| Keith Bannister | Page 26
The Richness and Beauty of the Physics
of Cosmological Recombination
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Chluba & Sunyaev A&A, 458, L29 (2006)
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well defined quasiperiodic spectral
dependence
photons are coming
from redshifts
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– z 1300−1400
– i.e. before the time of
the formation of the
CMB angular
fluctuations
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Observing
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All sky so dish size is not relevant
Needs a wideband spectrograph in 2-10 GHz range
Can measure multiple independent patches of sky
– Many dishes/receivers
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Need lowest possible Tsys
Can integrate over all oscillations
– Spectral dependence is accurately predicted
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Sensitivity Required
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-8
Need ΔT/T = 10
Tsys = 25K
10
Δν = 10 Hz
2 pol
100 antennas
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Time = 1month (3.10 sec)
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6
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ΔT/T = 25/(√(10 . 2.100.3.10 .)) = 10 !
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