Global EoR Experoments

1. Global EoRExperoments Ron Ekers, CSIRO CAASTRO Global EoR Workshop Uluru, 17 July 2013

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

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

4. The 21cm EoR challenge • Global T ~30mK in few MHz • S/N easy – can reach a few mK in few hours • T/T < 10-4 to10-5 • Calibrate the complex gain • 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 Zero spacing interferometer Zero spacing interferometer

5. From CoRE to ZEBRA CoRE (Chippendale)  ZEBRA  SARAS  ZEBRA II CSIRO RRI Calibratablereceiver MRO

6. COREfrequency independent antenna beam

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

8. Zebra – fat dipole v1

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

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

11. Building resistive screen

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

13. 3.4m ZEBRA – interferometerfirst CMB correlation 20 Jan 2011 • 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

14. ZEBRA at Gauribidanur

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

16. SARAS receiver evolution

17. SARAS receiver • 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

18. SARAS internal reflections • Short connections to keep broad bandwidth • Long connections to decrease coupling

19. SARAS internal reflections • Short connections to keep broad bandwidth • Long connections to decrease coupling

20. SARAS waterfall plot

21. Pulse calibration ? • Inject and integrate short (sec) pulses • Calibrated noise spectrum • Understand & calibrate reflections • NipanjanaPatra, Paul Roberts Pulse injected at Parkes vertex Pulse reflected from Parkes focus

22. Pulse calibration • Band limited pulse with -20db reflection • Pulse repetition rate 106 Hz • Accuracy 0.05%

23. Other Global EoR Experiments • WSRT: • Lunar occultation • EDGES: Rogers & Bowman • Polynomial fits Δz > 0.06 • Absolute calibration of components for wider bandwidths • BIGHORNS: Sokolowski, Tremblay, Wayth, Tingay⑫ • Low rfi site, high stability • Core II: Bannister, Chipendale, Dunning ① • Precision self calibrating receiver • DARE • Go to moon to avoid ionosphere and rfi

24. 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

25. BIGHORNS • Sokolowski, Tremblay, Wayth, Tingay⑫ • Low rfi site, high stability • Dynamic spectrum normalised by the median • Dynamic range 2% • Required 10-4 200MHz Day

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

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

28. Observing • 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 • Need lowest possible Tsys • Can integrate over all oscillations • Spectral dependence is accurately predicted

29. Sensitivity Required • Need ΔT/T = 10-8 • Tsys = 25K • Δν = 1010 Hz • 2 pol • 100 antennas • Time = 1month (3.106sec) • ΔT/T = 25/(√(1010 . 2.100.3.106 .)) = 10-8 !