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C-Band All Sky Survey (C-BASS)

C-Band All Sky Survey (C-BASS). J. P. Leahy (PI, Manchester), M. E. Jones (PI, Oxford) Clive Dickinson (JPL) AIMS: Definitive survey of Galactic synchrotron radiation and its polarization Anchor for synchrotron emission in future CMB polarimetry experiments up to CMBPOL.

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C-Band All Sky Survey (C-BASS)

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  1. C-Band All Sky Survey(C-BASS) J. P. Leahy (PI, Manchester), M. E. Jones (PI, Oxford) Clive Dickinson (JPL) AIMS: • Definitive survey of Galactic synchrotron radiation and its polarization • Anchor for synchrotron emission in future CMB polarimetry experiments up to CMBPOL. • Prototype for possible ground-based surveys at frequencies up to CMB band: 10, 15, 30… GHz • New window on Galactic magnetic field and cosmic rays BPOL workshop 27th October 2006

  2. Galactic foregrounds WMAP polarized brightness: 23 GHz, 4° beam • Sky is full of polarized interstellar synchrotron emission • 91% of pixels detected at this resolution • All components have significant spectral variations We must have more measurements than parameters! BPOL workshop 27th October 2006

  3. B-POL probably has primary frequencies at ≥ 90 GHz Satellite → nearly all sky survey: not just regions of minimum foreground Even at 90 GHz, extrapolation of 22 GHz WMAP polarization outside P06 mask (73% of sky) is larger than r=0.1 B-mode signal For r=0.002, signal is 7 times weaker We must correct for synchrotron emission to get even close to B-POL sensitivity requirements, even for >90GHz. C-BASS Dust? C-BASS motivation B 90 GHz Synch. CLOVER Noise Lensing BPOL workshop 27th October 2006

  4. Synchrotron spectral are smooth! • Power law is just an approximation… • …but a good one • The best-measured synchrotron sources are well fit by a 2nd-order log-log polynomial over 2 decades of frequency BPOL workshop 27th October 2006

  5. The Penticton Survey • Wollaben, Landecker, Reich & Wielebinski (2006) • survey of northern sky polarization at λ21 cm with Pentiction 25-m dish • Comparison with WMAP: • Spectral index β: • T(ν) = T0 (ν/ν0)β • Faraday rotation RM: • χ(ν) = χ0 + RM λ2 • Depolarization: • Unresolved RM structure BPOL workshop 27th October 2006

  6. Spectral Index 21:1.3 cm BPOL workshop 27th October 2006

  7. Affected by depolarization @ λ21cm, especially near Galactic plane Tail of relatively flat apparent spectral indices Relatively well-defined peak at βP =−3.2 Seems unaffected by depol. C.f. usual assumptions: (− 2.7 ≥β ≥−3) Polarized emission steeper than total? Less contaminated by free-free, spinning dust? Spectral Index 21:1.3 cm BPOL workshop 27th October 2006

  8. Low sensitivity in WMAP data at λ < 1.3 cm gives limited sky coverage Note flat spectrum for Crab nebula Mean βP≈ −3.0 Slightly flatter than at lower frequencies. (−3.1 in same regions) Spectral Index: 1.3:3 mm BPOL workshop 27th October 2006

  9. Dust polarization well measured by Planck Synchrotron dominates, at best, only in lowest Planck channels need extra info to fix spectrum. WMAP takes us down only to 23 GHz weak lever arm for extrapolation Gap between 2.4 and 23GHz Ground-based surveys needed to fix synchrotron emission Thermal Dust Anomalous Dust Faraday Rotation Pinning down the Galactic synchrotron spectrum BPOL workshop 27th October 2006

  10. Dust polarization well measured by Planck Synchrotron dominates, at best, only in lowest Planck channels need extra info to fix spectrum. WMAP takes us down only to 23 GHz weak lever arm for extrapolation Gap between 2.4 and 23GHz C-BASS fills the gap! Thermal Dust Anomalous Dust Faraday Rotation Pinning down the Galactic synchrotron spectrum BPOL workshop 27th October 2006

  11. Novel purpose-built single-feed polarization and total power receiver (Manchester/Oxford) Northern survey from OVRO 5.5 m dish (California) sub-reflector tripod designed for low spillover high accuracy surface (mm-λ telescope) Southern survey from 7.6 m at Karoo (KAT) site, South Africa high quality communication antenna Exquisite control of spillover new, large sub-reflectors ground screens & baffles simulations & measurements The Survey OVRO 5.5 m BPOL workshop 27th October 2006

  12. Receiver: combining technologies • Novel architecture: analogue correlation radiometer + polarimeter • Unique ultra-stable cold load (collaboration with RAL) • Draws on current technology (e-MERLIN, Clover, Planck) • e-MERLIN amplifiers: broad-band, low-noise • correlation receiver prototyped under Oxford Experimental Cosmology grant BPOL workshop 27th October 2006

  13. FWHM resolution 52 arcmin Same as 408MHz survey Smooth to 1º for high-latitude analysis, to reduce pixel noise Sensitivity: < 0.1 mK / beam rms. Extrapolated map at 60GHz has SNR > 2 for 90% of pixels even at high latitudes (outside WMAP polarization mask ‘P06’) Timescale: Complete by end 2010 Northern survey released 2009 Survey Parameters 7.6 m Telescope BPOL workshop 27th October 2006

  14. Survey Strategy • Based on Effelsberg experience • Long, fast sweeps • small dish can be scanned rapidly! • Full coverage of one quadrant of the sky after ~ 1 week. • Many observations per pixel • spread over many months • several different parallactic angles • Gives redundancy and robustness of polarization solution • Bonus: transients! Example 1-night coverage High sensitivity allows identification & control of systematics BPOL workshop 27th October 2006

  15. FUNDED FUNDED Project Partners • Manchester: • front end systems and backend amps & filters • low-level and calibration software • Oxford: • cryostat, cold load, polarimeter and detectors, sub-reflector, optical design • mapping software • Caltech: • 5.5 m telescope, ground screen/baffles, digital backend, control, site support • Rhodes/HartRAO: • 7.6 m telescope, ground screen/baffles, site support All partners contribute to observations, analysis & interpretation BPOL workshop 27th October 2006

  16. Impact of C-BASS • Planck alone → Planck + C-BASS • Typical high-latitude pixel (2° beam): • Spectral index bias • Stokes I: −0.14 → 0.015 • Stokes Q,U: −0.16 → 0.03 • 70 GHz synchrotron amplitude error (assuming straight spectrum) • Stokes I σ: 0.9μK→ 0.3 μK (SNR: 3.5 → 12) • Stokes Q,U σ: 0.3 μK→ 0.045 μK (SNR: 1 → 7) • 70 GHz synch. Amp. Bias • Stokes I: 0.9 μK→ 0.15 μK • Stokes Q,U: 0.015 μK→ 0.003 μK 5-7 times reduction in systematic synchrotron residuals in the CMB Band! BPOL workshop 27th October 2006

  17. C-BASS: Summary • C-BASS provides anchor for polarized synchrotron spectrum • c.f. also Parkes 2.3 GHz survey (Caretti et al.) • Requires at least one more frequency close to primary CMB frequencies to fix synchrotron spectral index (70-90 GHz) • We probably need 1 or 2 more intermediate frequencies, e.g. 10-15 GHz; 30-40 GHz • Fix spectral curvature • Check for polarized emission from anomalous dust, free-free • Can be obtained from ground/ VLDF balloon (especially if we can calibrate very large scales from space). BPOL workshop 27th October 2006

  18. Staff: 0.8 FTE Academic 3 FTE PDRA 1.2 FTE Engineer 2 FTE Technician Direct costs £215k Equipment £104k T & S: £22k Estate & indirect £158.6k UK Costings (PRD grant) FEC Total: £500k (pre-FEC: £416k) BPOL workshop 27th October 2006

  19. UK Phasing • As suggested by PPARC secretariat: • C-BASS PRD Bid: • Receiver design & construction • Commissioning • C-BASS Exploitation Grant • submitted June 2007 • Observation, analysis, publication • Future Project bid • Submission 2009 if justified by C-BASS, CLOVER et al. • 10 GHz survey exploiting C-BASS technology BPOL workshop 27th October 2006

  20. C-BASS as a PRD scheme • Exploitation of PPARC technology infrastructure? • World-class Expertise and equipment at Jodrell Bank and Oxford • High-Priority Science? • Internationally identified as such (e.g. Dark Energy Task Force report) • Novel technology? • New receiver architecture; stabilised cold load • Paves the way for UK intellectual leadership in international projects? • Provides leadership of international C-BASS project, and likely successor at 10GHz • Paves the way for UK industrial return? • A 10 GHz multi-feed system would involve industrial contracts for receiver components (~ £1M) and possibly for custom telescopes (~£1M) • Pre-construction phase? • Exploratory research for a major instrument at 10 GHz, as well as versatile working 5 GHz instrument BPOL workshop 27th October 2006

  21. Timeliness • Planck proprietary period ends Q1 2011 • We must start now to complete C-BASS (North & South) in time to incorporate in official Planck analysis. • Similar time-line for ground-based and balloon B-mode experiments (Clover, BICEP, QUIET, EBEX, SPIDER…). BPOL workshop 27th October 2006

  22. C-BASS Workpackage Breakdown WP 1 Project Management TJP/JPL/MEJ/JLJ WP 2 Rx Design Richard Davis WP 3 Optics Design Mike Jones WP 4 Survey Design Paddy Leahy WP 5 OVRO RFI Characterisation Tim Pearson WP 6 Karoo RFI Characterisation Justin Jonas WP 7 Rx Construction Mike Jones WP 8 Rx Integration Mike Jones WP 9 Rx Testing (UK) Paddy Leahy WP 10 Software Tim Pearson WP 11 Prepare 5 m Telescope Tim Pearson WP 12 Rx Shipping & Installation/OVRO Mike Jones WP 15 Northern Survey Operations Tim Pearson WP 16 Northern Data Analysis PDRA WP 18 Prepare 7.6 m Telescope Justin Jonas WP 13 OVRO Commissioning Tim Pearson WP 14 Write technical Papers PDRA WP 17 PR & Outreach Erik Leitch WP 19 Rx Shipping & Installation/Karoo Tim Pearson WP 20 Karoo Commissioning Justin Jonas WP 21 Southern Survey Operations Justin Jonas WP 22 Southern Data Analysis PDRA WP 23 Combine Surveys PDRA WP 24 Foreground Analysis Clive Dickinson

  23. C-BASS WP Breakdown WP 2 Rx Design R. J. Davis WP 2.1 Specify Mechanical I/F WP 2.2 Specify JBO/Oxford I/F WP 2.3 Specify Oxford/CCB I/F WP 2.4 Design Rx Cryo Components WP 2.5 Design Rx Backend WP 2.6 Design Cold Load WP 2.7 Design Cryostat WP 2.8 Design Polarimeter WP 2.9 Adapt CCB design WP 3 Optics Design M. E. Jones WP 3.1 OVRO Ground Screen WP 3.2 5 m Subreflector WP 3.3 5 m Feedhorn WP 3.4 Karoo Ground Screen WP 3.5 7.6 m Subreflector WP 3.6 7.6 m Feedhorn

  24. C-BASS WP Breakdown WP 7 Rx Construction M. E. Jones WP 7.1 RF cryo components WP 7.2 Backend amps & filters WP 7.3 Cold Load WP 7.4 Cryostat WP 7.5 Phase switch system WP 7.6 Detectors WP 7.7 Feedhorn WP 7.8 CCB WP 9 Rx Testing J. P. Leahy WP 9.1 White Noise optimization WP 9.2 Bandpass measurement WP 9.3 1/f noise optimisation WP 9.4 Noise diode WP 9.5 Polarization purity WP 9.7 Cold Load Stability WP 9.9 Backend modes WP 9.6 Phase stability & zero point WP 9.8 Feed radiation pattern

  25. C-BASS WP Breakdown WP 10 Software Tim Pearson WP 10.1 Data logging WP 10.2 Quick-Look Software WP 10.3 Calibration Software WP 10.4 Mapping Software WP 10.5 Foreground Analysis S/W WP 15 Northern Ops Tim Pearson WP 15.1 Night-time Scheduling WP 15.2 Preventative Maintenance WP 15.3 Far-sidelobe Mapping WP 15.4 Main Beam Mapping WP 15.5 Cryo Maintenance

  26. E-Merlin C-band LNA: 1/f knee, with differencing, ~1mHz Allows full rotation scan at ~ 1°/sec Several times faster in practice Technology in place: BPOL workshop 27th October 2006

  27. Holy Grail for CMB work: ‘smoking gun’ of inflation: B-mode polarization from gravitational waves < 3% of small-scale E-modes that are already detected. Accurate E/B separation needs contiguous large solid angle. If B-modes too weak, masked by gravitational lensing converting E→B B C-BASS Motivation E r = 0.1 Lensing BPOL workshop 27th October 2006

  28. 5 GHz because… • Halfway between quasi-reliable surveys at 1.4 GHz (Stockert, Reich & Reich) and 23 GHz (WMAP). • Expected high-latitude Faraday rotation a few degrees, c.f. ~30° at 2.3 GHz. • Residual correction at high latitude via 1.4 GHz polarization survey from Penticton/Villa Elisa (Wolleben/Testori et al.) • Below main emission from anomalous dust, so predominantly synchrotron. • Signal still strong enough (few mK) to map the sky in a reasonable time (< 1 year) with a single receiver. BPOL workshop 27th October 2006

  29. Impact of C-BASS • Planck alone → Planck + C-BASS • Typical high-latitude pixel (2° beam): • Spectral index bias • Stokes I: −0.14 → 0.015 • Stokes Q,U: −0.16 → 0.03 • 70 GHz synchrotron amplitude error (assuming straight spectrum) • Stokes I σ: 0.9μK→ 0.3 μK (SNR: 3.5 → 12) • Stokes Q,U σ: 0.3 μK→ 0.045 μK (SNR: 1 → 7) • 70 GHz synch. Amp. Bias • Stokes I: 0.9 μK→ 0.15 μK • Stokes Q,U: 0.015 μK→ 0.003 μK 5-7 times reduction in systematic synchrotron residuals in the CMB Band! BPOL workshop 27th October 2006

  30. A Proof of Concept • The SPLASH survey (Abidin et al 2004) used the Effelsberg dish at 1.4GHz to measure faint synchrotron polarization at high Galactic Latitude. • Absolute polarization levels recorded to within ± 8 mK, ~10% of mean signal. • Limited by relatively infrequent (90 min cycle) calibration to counter baseline drifts. BPOL workshop 27th October 2006

  31. Data Analysis • Npix ~ 5x105 (cf Planck ~ 5x107) • Ndata ~ 109 (cf Clover ~ 1013) • Long-solved problem (e.g. Haslam et al 1981) • Improved techniques for eliminating residual striping, but all algorithms  Ndata • No higher powers of N BPOL workshop 27th October 2006

  32. Competition? • “Galactic Emission Mapping” • Recently began preparation for 5 GHz polarization survey • Operational at various frequencies since 1991 • No results to date • Originally intended to complement COBE • Sensitivity too low to achieve goals of C-BASS • 10 x noisier GEMBrazil BPOL workshop 27th October 2006

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