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Global EoR Experoments Ron Ekers, CSIRO CAASTRO Global EoR Workshop Uluru, 17 July 2013

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Summary n Strategy for technically difficult experiments –Either masochists or people who don’t know any better! –NB the Crick and Watson story on DNA structure n Global HI EoR v imaging HI EoR –Statistical v direct detection n CORE ZEBRA SARAS n Other global HI experiments –EDGES, BIGHORNS, COREII, DARE, n Pulse calibration n Epoch of (re)combination July 20132

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Global HI EoR prediction n Pritchard et al, Nature 468, 772 (2010) Z = 6.3 Peter Shaver conjecture (200/65) 2.5 =17

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The 21cm EoR challenge n Global T ~30mK in few MHz –S/N easy – can reach a few mK in few hours n T/T < 10 -4 to10 -5 n Calibrate the complex gain n Minimize the number of unknowns that can couple to EoR n Remove the forgrounds n 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 Zero spacing interferometer

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From CoRE to ZEBRA CoRE (Chippendale) ZEBRA SARAS ZEBRA II Calibratable receiver CSIRO RRI MRO July 20135

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CORE frequency independent antenna beam

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Global EoR system RRI Bangalore Ravi Subrahmanyan Ron Ekers Peter Shaver A. Raghunathan

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Zebra – fat dipole v1

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ZEBRA Global EoR Experiment n ZEro-spacing measurement of the Background RAdio spectrum n Partially reflecting resistive screen n Virtual zero spacing interferometer n Removes all additive errors n Modulate screen ? Subrahmanyan, Ekers Patra Partial reflector/transmitter X

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The space beam-splitter: a resistive wire mesh n Need a space beam-splitter before the antenna n A lossless screen (e.g. a conducting grid) –transmitted & reflected waves are orthogonal n 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 n Lumped resistance on scale << –Practical solution instead of resistance wire

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Building resistive screen

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The Resistive Screen copper wire + lumped resistors resistor value = free space impedance/2 3x4 metres holes to reduce wind loading Roll up for transport

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ZEBRA – interferometer first CMB correlation 20 Jan 2011 3.4m n 1.5m separation n Max sky coverage at zero spacing 26% n Contributions to correlated output –Global sky signal –Screen radiating –1.5m interferometer sky correlation »One path through screen »Both paths miss screen Ferrite absorber

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ZEBRA at Gauribidanur

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Zebra correlated output n Baseline ripple –changes with LST –Repeats each day –Multipath scattering of galaxy foreground signal –Shifted location …….

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SARAS receiver evolution

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SARAS receiver n Patra & Subramanyan, EA (2013) n 88-175MHZ n Differential correlation spectrometer n Digital correlator well separated from receiver n Minimize number of parameters in solution (11) n Solve for multipath propagation from internal reflections n Eg noise from receiver input

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SARAS internal reflections n Short connections to keep broad bandwidth n Long connections to decrease coupling

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SARAS internal reflections n Short connections to keep broad bandwidth n Long connections to decrease coupling

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SARAS waterfall plot

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Pulse calibration ? Pulse injected at Parkes vertex Pulse reflected from Parkes focus n Inject and integrate short ( sec) pulses n Calibrated noise spectrum n Understand & calibrate reflections n Nipanjana Patra, Paul Roberts

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Pulse calibration n Band limited pulse with -20db reflection n Pulse repetition rate 10 6 Hz n Accuracy 0.05%

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Other Global EoR Experiments n WSRT: –Lunar occultation n EDGES: Rogers & Bowman –Polynomial fits Δz > 0.06 –Absolute calibration of components for wider bandwidths BIGHORNS: Sokolowski, Tremblay, Wayth, Tingay ⑫ –Low rfi site, high stability Core II: Bannister, Chipendale, Dunning ① –Precision self calibrating receiver n DARE –Go to moon to avoid ionosphere and rfi July 201323

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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 Rogers & Bowman (EDGES memo #99)

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BIGHORNS Sokolowski, Tremblay, Wayth, Tingay ⑫ –Low rfi site, high stability n Dynamic spectrum normalised by the median n Dynamic range 2% –Required 10 -4 Day 200MHz

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CORE2: A global EOR experiment with a self- calibrating receiver on two antennas CORE2: A global EOR experiment with a self-calibrating receiver and two antennas| Keith Bannister | Page 26 CORE2-MONO 60 Degree beam Optimised for frequency Independence and low RFI and CORE2-DISH 5 Degree beam Optimised for foreground removal

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27 The Richness and Beauty of the Physics of Cosmological Recombination n well defined quasi- periodic spectral dependence n photons are coming from redshifts – z 1300−1400 –i.e. before the time of the formation of the CMB angular fluctuations n Chluba & Sunyaev A&A, 458, L29 (2006)

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28 Observing n All sky so dish size is not relevant n Needs a wideband spectrograph in 2-10 GHz range n Can measure multiple independent patches of sky –Many dishes/receivers n Need lowest possible Tsys n Can integrate over all oscillations –Spectral dependence is accurately predicted

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29 Sensitivity Required n Need ΔT/T = 10 -8 n Tsys = 25K n Δν = 10 10 Hz n 2 pol n 100 antennas n Time = 1month (3.10 6 sec) n ΔT/T = 25/(√(10 10. 2.100.3.10 6.)) = 10 -8 !

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Challenge: Low frequency foreground – hot, confused sky HI 21cm signal ~ 10 mK Foreground: T ~ 100 z)^-2.6 K Highly ‘confused’: 1 source/deg^2.

Challenge: Low frequency foreground – hot, confused sky HI 21cm signal ~ 10 mK Foreground: T ~ 100 z)^-2.6 K Highly ‘confused’: 1 source/deg^2.

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