BPOL workshop 27 th October 2006 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 27 th October 2006 Galactic foregrounds 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! WMAP polarized brightness: 23 GHz, 4° beam

BPOL workshop 27 th October 2006 Foreground brightness Smoothing removes emission that fluctuates on scales smaller than the beam –E.g. CMB ‘E-modes’ Similar amplitudes at 2° and 4°: –Looking at signal, not noise! –Polarization has little small- scale structure. (Foreground, high latitude) At 4° resolution, polarization clearly detected in 91% of pixels Median: GHz Histogram of polarization values at 22.5 GHz, 4° beam, with various masks

BPOL workshop 27 th October ° Pol. Maps in other bands 33 GHz 41 GHz 61 GHz94 GHz

BPOL workshop 27 th October 2006 C-BASS motivation CMB polarization splits into orthogonal modes: E-modes fix optical depth to re-ionization –dramatic reduction in parameter degeneracy B-modes define energy scale of inflation Obscured by Galactic foreground emission –minimum at ~60 GHz –synchrotron below –dust above. T B E

BPOL workshop 27 th October 2006 C-BASS motivation: 60 GHz E-modes fix optical depth to re-ionization –dramatic reduction in parameter degeneracy B-modes define energy scale of inflation Obscured by Galactic foreground emission –minimum at ~60 GHz –synchrotron below –dust above. Lensing E B 60 GHz r = 0.1 C-BASS

BPOL workshop 27 th October 2006 C-BASS motivation Lensing CLOVER Noise B 90 GHz Synch. 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 > 90 GHz. C-BASS

BPOL workshop 27 th October 2006 Galactic Science Faraday-free polarization → Reliable magnetic field directions at medium & high latitudes: local disk and halo field lines (more distant than starlight polarization) GHz spectra allows tracking of both low-frequency spectral index and high-frequency curvature of synchrotron spectrum across the sky –Initial spectral index characteristic of acceleration sites –Convex curvature is signature of radiative losses –Concave curvature (if present) suggests preferential diffusion of high-energy cosmic ray electrons New diagnostics for life-cycle (acceleration, diffusion, energy loss) of cosmic rays in the Galaxy.

BPOL workshop 27 th October 2006 Foreground Separation Template fitting: –Using external templates (Hα etc) –Blind template construction (FASTICA etc) Spectral fitting: –Independent analysis at each resolution element –Requires high S/N in large majority of pixels, at least at one frequency per foreground

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

BPOL workshop 27 th October 2006 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) = T 0 (ν/ν 0 ) β Faraday rotation RM: –χ(ν) = χ 0 + RM λ 2 Depolarization: –Unresolved RM structure

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

BPOL workshop 27 th October 2006 Spectral Index 21:1.3 cm Affected by λ21 cm, especially near Galactic plane –Tail of relatively flat apparent spectral indices Relatively well-defined peak at β P = −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?

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

BPOL workshop 27 th October 2006 Faraday Rotation

BPOL workshop 27 th October 2006 Faraday Rotation Away from Galactic plane, RMS Faraday rotation between λ1.3 cm and λ21 cm is 33° –< 3° at 6 cm –< 0.2° at 1.3 cm Significantly less than Faraday rotation of extragalactic sources –Diffuse synchrotron emission is mixed with ionized layer. PA differences between WMAP bands (22.5 – 33 GHz) suggest large Faraday rotation near Galactic Centre: –3°-4° at 1.3 cm, –RM ≈−700 rad m -2 A few pixels show up to 22° rotation between GHz –Random errors (~ 5σ, but non- Gaussian) –Change of emission mechanism (dust polarization?) –Very large RM??

BPOL workshop 27 th October 2006 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 23 GHz Ground-based surveys needed to fix synchrotron emission Thermal Dust Faraday Rotation Anomalous Dust Pinning down the Galactic synchrotron spectrum

BPOL workshop 27 th October 2006 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 23 GHz C-BASS fills the gap! Thermal Dust Faraday Rotation Anomalous Dust Pinning down the Galactic synchrotron spectrum

BPOL workshop 27 th October 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 27 th October 2006 Impact of C-BASS C-BASS adds value to all future CMB polarization experiments (Planck, Clover, B-pol etc) –Planck (& Clover) alone hardly constrain synchrotron emission in the CMB band (~ 60 GHz) –with C-BASS, get 5-7 times better C-BASS will be the definitive 5 GHz survey: will be cited for decades

BPOL workshop 27 th October 2006 The Survey 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 OVRO 5.5 m

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

BPOL workshop 27 th October 2006 Receiver Architecture Balanced radiometer + polarimeter, All-RF system, 20% bandwidth E-MERLIN 4-8 GHz LNA, T sys < 20 K, BW  1 GHz Analogue correlation polarimeter Current technology (e.g. MERLIN, Planck) except for cold load

BPOL workshop 27 th October 2006 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 27 th October 2006 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 FUNDED

BPOL workshop 27 th October 2006 An Experienced Team Mike Jones: –CAT, VSA, AMI, Clover, SKA Paddy Leahy: –Polarimetry with Planck, Effelsberg, VLA etc Tim Pearson: –CBI, CCB, PGPLOT Justin Jonas: –Rhodes/HartRAO 2.3 GHz survey Richard Davis: –Planck Radiometer Working Group (Chair), MERLIN telescope at Cambridge, VSA Peter Wilkinson –SKA, VLBI etc Ghassan Yassin –Clover, CAT, VSA optics Rod Davies –Tenerife experiments, VSA, Planck Angela Taylor –VSA, AMI, CBI, Clover + experienced US & SA teams.

BPOL workshop 27 th October 2006 PDRA Tasks (18 month PRD period) Manchester –OMT & polarizer design and simulations –Other RF design, contribution to construction & integration –RF Testing –Calibration & foreground modelling software –Scan strategy simulations –Commissioning at OVRO –Paper preparation Oxford –Radiometer/polarimeter design and simulations –Contribution to Radiometer/polarimeter development, & integration –Optics simulations of telescopes & groundscreen –mapping simulations & software –Testing polarimeter and cold load –Commissioning at OVRO –Paper preparation Vital experience for effective contribution to operations phase – continuity essential!

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

BPOL workshop 27 th October 2006 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 GHz; 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 27 th October 2006 UK Costings (PRD grant) 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 FEC Total: £500k (pre-FEC: £416k)

BPOL workshop 27 th October 2006 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 27 th October 2006 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 10 GHz 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 27 th October 2006 Timeliness Planck proprietary period ends Q 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…).

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 7 Rx Construction Mike Jones WP 8 Rx Integration Mike Jones WP 9 Rx Testing (UK) Paddy Leahy WP 5 OVRO RFI Characterisation Tim Pearson WP 6 Karoo RFI Characterisation Justin Jonas WP 11 Prepare 5 m Telescope Tim Pearson WP 10 Software Tim Pearson WP 12 Rx Shipping & Installation/OVRO Mike Jones WP 13 OVRO Commissioning Tim Pearson WP 14 Write technical Papers PDRA WP 16 Northern Data Analysis PDRA WP 18 Prepare 7.6 m Telescope Justin Jonas 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 WP 15 Northern Survey Operations Tim Pearson WP 17 PR & Outreach Erik Leitch

WP 2 Rx Design R. J. Davis WP 2.2 Specify JBO/Oxford I/F WP 2.1 Specify Mechanical 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 m Subreflector WP 3.1 OVRO Ground Screen WP m Feedhorn WP 3.4 Karoo Ground Screen WP m Subreflector WP m Feedhorn WP 2.3 Specify Oxford/CCB I/F C-BASS WP Breakdown

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

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

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

BPOL workshop 27 th October 2006 C-BASS Motivation 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 Lensing E B r = 0.1

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

BPOL workshop 27 th October 2006 A Proof of Concept The SPLASH survey (Abidin et al 2004) used the Effelsberg dish at 1.4 GHz 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 27 th October 2006 Data Analysis N pix ~ 5 x 10 5 (cf Planck ~ 5 x 10 7 ) N data ~ 10 9 (cf Clover ~ ) Long-solved problem (e.g. Haslam et al 1981) Improved techniques for eliminating residual striping, but all algorithms  N data –No higher powers of N

BPOL workshop 27 th October 2006 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 GEM Brazil